snakes
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Snakes (plural of snake , from Middle High German slange ; to sling , to squirm , to bend, to loop, to creep; ancient Greek ὄφεις ópheis ; Latin serpentes , related to ancient Greek ἕρπειν herpein , German 'crawl' ) are a subordination of the scale creeping animals . They descend from lizard-like ancestors. Compared to these, the body is greatly elongated and the extremities have almost completely receded. Today over 3600 species have been described. With the exception of the Arctic , Antarctic , permafrost areas and some islands, they can be found in all habitats worldwide.
Snakes play a major role in cultural history and mythology and, based on this, also in art and literature: In the Old Testament creation story of the Bible, a snake seduced Adam and Eve into tasting the fruit of the tree of knowledge . The staff of Asclepius , wound around by a snake, in Greek mythology ( Aesculapian staff ) is the symbol of the medical and pharmaceutical professions to this day.
features
outer appearance
All snakes have an elongated and thin body and with a few exceptions have completely lost their limbs. Remnants of the pelvic girdle and short anal spurs can only be found in some evolutionarily primitive snakes, such as roller and blind snakes . The body shapes can vary greatly from species to species. Some snakes can look rather stocky and have a thick body with a short tail, for example the Gaboon viper ( Bitis gabonica ), while others become very evenly thinner towards the rear, for example the rough grass snake ( Opheodrys aestivus ). They vary in cross-section from round or oval to triangular. The stomach is almost always flattened. The size of adult snakes varies greatly, depending on the species, between 10 centimeters for the slender blind snake ( Tetracheilostoma carlae ) and almost 7 meters for the reticulated python ( Python reticulatus ).
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Snakes lick their mouths closed.
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Slow snakes , on the other hand, have to open their mouths to lick the tongue.
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In contrast to the Sneak (Anguidae) having a plurality of rows of abdominal shields, snakes have only one row thereof. Furthermore, their rostral shield has a small notch on the lower edge (the so-called rostral notch), which allows them to lick without opening their mouths. Sneak doesn't have this notch. Snakes also have no eyelids , their eyes are completely covered by a transparent scale . This is different with sneaking, which can be seen from the blinking of the animals. Furthermore, sneaks are capable of autotomy , in case of danger they can shed their tail. This ability also distinguishes them from snakes, whereby the tail of some evolutionarily old, underground snake species can also break off, but there it is a passive process and it no longer grows back.
An extremely conspicuous sexual dimorphism occurs only very rarely; For example, female adders ( Vipera berus ) tend to be brown to reddish in color without a particularly high-contrast pattern, while the males are more gray in color and their markings stand out in contrast to the basic color. As a further example, different scale forms are mentioned: the females of the Sipo ( Chironius carinatus ) have smooth scales, while those of the males are keeled. Further gender-related differences can only be determined in a direct comparison: the females are usually somewhat larger and more extensive than the males, but it can also be the other way around. The base of the tail behind the cloaca is a good distinguishing feature. While it tapers very evenly in the males, a heel can be seen in the females.
Snakes have a large number of color and drawing variants. They encompass all colors of the spectrum and can range in one color, with little colored scales, through stripes, ladder and checked patterns to complex color combinations. Some nontoxic species have evolved into a pattern similar to that of poisonous species in order to confuse and protect themselves ( mimicry ) their enemies . Special pigmentations such as albinism and melanism also occasionally occur in snakes .
skin
Snakeskin consists of three layers: the epidermis (upper skin), the dermis (dermis) and the subdermis (lower skin). All layers fulfill different functions. The epidermis consists of keratin-containing cells that form a dense and flexible horny layer. This is arranged in the form of scales . The epidermis represents the barrier between the snake's body and the environment, through it the animal is reliably protected from harmful environmental influences. In the dermis there are nerve endings , collagen-containing connective tissue , blood vessels and pigment cells ( chromatophores ). Here the snake receives tactile impressions and the pigments stored here give it its color. The subdermis contains fatty bodies in which energy reserves are stored, for example for hibernation or, in ovoviviparous snakes, for the period of pregnancy.
Dandruff
Snake scales are divided into head and body scales. In some species (such as vipers ) the head shields are quite large in relation to the body scales and can serve as a distinguishing feature. Six different head shields can be seen in the top view: Scutum rostrale (snout shield, usually present once), Scutum internasale (between nasal shield , twice), Scutum praefrontale (front forehead shield, twice), Scutum frontale (forehead shield, once), Scutum supraoculare (over-eye shield , twice) and parietal scutum (parietal shield, twice). There are also various groups of shields in the side view of the head, but the number of scales can vary greatly from species to species. These are: Scutum nasale (nasal shield), Scutum loreale ( rein shield), Scutum praeoculare (shield), Postoculare (shield behind the eye), Scutum temporale (temple shield ), Scutum supralabiale (upper lip shield ), Scutum sublabiale (lower lip shield ) and Scutum suboculare ( lower lip shield ). In many other species (for example the vipers ) the scaling just presented is fragmented into many small scales.
The small body scales on the back and the side are usually arranged in the form of longitudinal rows and overlap the scales behind them. Here, too, there are exceptions, such as some sea snakes whose scales do not overlap but are arranged side by side; this creates the advantage that marine skin parasites cannot establish themselves well. On the belly, the scales run across the entire width of the body, so snakes only have a row of belly scales. Here, too, the scales overlap those behind them. Scales can be designed very differently, there are shiny, matt, smooth or even keeled specimens. Some have very specific functions; Probably the best-known example is the rattlesnake's tail rattle ; this consists of special scales formed into horn rings.
All snake species have a special scale in common: this is transparent and serves to protect the eyes. Snakes do not have eyelids, their eyes are completely covered by said scale. Dirt or other foreign bodies could penetrate under the eyelids, which the animals could no longer get rid of.
Molting
Because snakes, like all reptiles, continue to grow for life after reaching sexual maturity, but their skin is not continuously sloughed off, as is the case with mammals , for example , they have to shed their skin completely on a regular basis. Air penetrates under the dying horny layer and slowly detaches it from the rest, which can be recognized by the cloudiness or matt color of the animals and especially the eyes. The underlying skin cells grow, form a new layer of skin and keratinize a short time later. As a result, the animal is never defenseless against possible external influences. When the keratinization of the new skin is complete, the snake begins to rub its snout on a sharp or pointed object. The old skin tears open and the snake tries to get free of it while crawling through narrow crevices or forks of branches, around branches or the like. After moulting, the animals have a firm and clearly colored skin again. The cornea of the eyes, which is also peeled off, is now clear again. The old skin, the exuvia , also known as the “adder shirt”, remains.
Bone structure
The bones present in snakes can be roughly divided into three groups: skull bones, vertebrae and ribs . The pelvic girdle bones already mentioned are rudimentary and have no other function. The shoulder girdle and sternum are also absent .
The snake skull is designed to be very flexible. Since the jaw and palate bones do not grow together, but are only connected by ligaments and can be moved very much, the mouth can be opened very wide. This enables the animals to devour larger prey in one piece. The upper jaw consists of the following bones: premaxillary (the only solid, above the prefrontal , connected to the skull), maxilla , wing bone , transverse palatine bone and palatal bone . The lower jaw consists of two lower arches. There is one dental arch in the lower and two in the upper jaw (one inner and one outer). These two arches are divided into two parts, analogous to the lower jaw. The outer row of teeth is used to catch and hold the prey, the inner row is used to transport it into the esophagus. The left and right arches alternately slide forward, grab the prey, slide backwards with it and detach from it, in order to slide forward again and start over. Since all jaw bones can be moved relatively independently of one another, they have to be "sorted" again after each bite or devouring prey by opening and closing the mouth several times.
The number of vertebrae is increased to around 200 to a maximum of 435. The vertebral bodies are connected to one another via an intervertebral disc and a joint . The joint socket is in front of the vertebra, the joint head behind. Inside they lead the spinal cord and blood vessels in a canal . Although two vertebrae are not able to bend or twist particularly sharply in relation to one another (since this would risk injuring or tearing the spinal cord), the animals are very mobile due to the high number of vertebrae (with around 40 vertebrae, a bend of around 60 ° can be achieved). Each vertebra, with the exception of the cervical and caudal vertebrae, has a pair of ribs. The ribs are connected to the vertebrae by a hinge and end freely. The joint allows a backward movement from the normal position and a resulting widening of the body. In addition to the extremely agile skull bones, this is another requirement for the snakes to devour prey that is larger in diameter than their own.
teeth
The snakes' teeth are not intended for chewing, but are only used to hold prey or, in the case of fangs, to inject toxins . They just sit loosely on the jaw and are not firmly attached to it. All teeth are directed backwards; If a prey tries to free itself from the snake's bite, its teeth only dig deeper into its body. If a tooth breaks off, it will be replaced. In most cases, reserve teeth have already been placed behind the existing ones, so that replacements are available in a relatively short time.
There are four different types of dentition in snakes:
- aglyph: snakes toothed like this have no fangs. All teeth are about the same size, have the same shape and are evenly distributed in the jaw. There are no special features of the teeth as in the other three types of teeth. These non-poisonous snakes include the real snakes (Colubrinae), giant snakes (Boidae), blind snakes (Typhlopidae) and slim blind snakes (Leptotyphlopidae).
- Proteroglyph: With this type of dentition, snakes have a pair of poisonous teeth that are located in the front area of the upper jaw. The poison teeth are slightly larger and thicker than the rest and have a groove on their inside (furrow teeth). The poison glands lie above in the connective tissue; if the snake bites, the poison is channeled through the furrow into the body of the prey. Representatives of the sea snakes (Hydrophiinae) and poisonous snakes ( Elapidae) are proteroglyph toothed; this also includes the snakes with the strongest poisons, such as the taipane .
- opisthoglyph: The structure of the fangs is comparable to the proteroglyph variant, in contrast to this, the pair of fangs sits in the back of the upper jaw. Are dentate Opisthoglyph the illusion snakes .
- solenoglyph: This type of dentition also has a pair of poisonous teeth in the front of the upper jaw. However, the fangs are relatively long (depending on the species between three and five centimeters) and are therefore folded back in a fold of connective tissue when the mouth is closed. The teeth are not furrowed, but their interior is - similar to a cannula - traversed by a tube through which the poison is passed (tubular teeth). As soon as the snake opens its mouth to bite, the poison teeth fold forward by about 90 ° and can be struck deep into the prey. A great advantage is that the poison is also brought deep into the body. From a purely mechanical point of view, the solenoglyph dentition is most effective for injection. All vipers (Viperidae) and pit vipers ( Crotalinae) are equipped with such tubular teeth.
- Teeth in snakes
Skull of the aglyphic dark tiger python
Skull of a proteroglyphic king cobra
Skull of the opisthoglyphic western hook-nosed snake
Skull of a solenoglyphic rattlesnake
Sense organs
Snakes are able to perceive and process stimuli from their environment in various ways. What they all have in common is the absorption of smells (volatile substances) through the nose and non-volatile fragrances with their forked tongue (nasovomeral sense). The forked tongue has encouraged people in the past to think about their function. It is seen in recognizing chemosensitive traces in order to be able to follow the tracks of pheromones or prey. The ability to rate two points at the same time improves the ability to differentiate and makes it easier to perceive gradients . Inside the mouth, they guide the tips of the tongue into the Jacobson organ , two small indentations on the roof of the mouth . There the fragrances are then analyzed, similar to the smells in the olfactory center . With the two tips, the snakes can perceive different scents at the same time and obtain spatial information from them. This enables them to track down and track prey or mating partners. The purpose of frequent licking is therefore to explore their surroundings.
Some species have developed sensory organs to perceive infrared radiation . The pit vipers have an organ (the pit organ that gives them their name ) with which they can do this. It is a sensory pit between the eye and the nostril, with the help of which temperature differences of up to 0.003 ° C can be registered. The giant snakes have developed a similar organ, the labial pits in them . These are located in the scales of the upper and lower lip. They are less sensitive than the pit organ and able to perceive temperature differences of up to 0.026 ° C. Both infrared sensory organs are only used to track down endothermic prey. These stand out very clearly from their surroundings, despite any camouflage they may have; especially at night, when the difference between ambient and body temperature is even greater than during the day. These sensory organs are not helpful for finding ectothermic prey. For this purpose, nasovomeral sense and eyes are used.
The eyes play a role in the sensory perception of snakes mainly in identifying other snakes (rivals or possible sexual partners), other animals (prey or predator) and orientation in space. There are many differently equipped eyes and accordingly the eyesight of the animals is differently well developed. Some species (mostly snakes that live underground) only have eyes equipped with rods , so they can only recognize differences in brightness of objects, not colors. Others only have cones and can therefore perceive colors. Unless they have infrared receptors, these species are restricted to daytime activity. The most developed eye shape shows cones and rods; Snakes equipped in this way can theoretically be active at any time, including at night and at dusk. There are also thin and thick cones, which can be found in different combinations with the others. How they work has not yet been clarified.
The hearing of snakes perceives sound waves transmitted through the air only very poorly or not at all, since there is no outer ear . However, they are able to register vibrations in the ground with their inner ear . The prerequisite for this is that the head is on the floor. The vibrations are then transmitted into the inner ear through a series of bones connected to the lower jaw. This process is comparable to the transmission of acoustic signals through the ossicles in the middle ear of mammals. Since the left and right halves of the lower jaw of a snake are not rigid, but rather connected by flexible straps, both halves of the lower jaw can be made to vibrate independently of one another. This also enables snakes to perceive direction.
If a larger living being moves towards the snake, it can assess this based on the strength of the vibrations and has usually already fled to a hiding place before the potential enemy reaches it.
Internal organs
The brain is located in the skull capsule. Most of your internal organs are elongated according to the shape of the body. With the exception of Boidae and Xenopeltidae, the left lung is mostly stunted or not developed at all, while the right lung can extend over up to two thirds of the body length, in some sea snakes even as far as the anus. This can also be clearly seen from the outside, when the body expands slightly with each breath. At the back, the trachea changes into an air sac ( tracheal lung ), from which the snake can meet its oxygen requirements in special situations (for example, when devouring a large prey, which sometimes compresses the trachea, or in sea snakes during long dives). In sea snakes it also serves as a hydrostatic organ . The liver also consists only of the right lobe, but extends over most of the body.
Depending on the preferred habitat, the single-chamber heart is in different positions. In tree-dwelling ( arboricolous ) snakes, it sits near the head, so that the brain is always adequately supplied with blood even in a vertical position (for example when climbing a tree). During this time, the back of the body is supplied by the action of the gravitational force of the earth , so there is no need to pump the blood to the heart. Such a snake can hold the upright position longer than other snakes, but has to keep standing horizontally, otherwise blood can build up in the back of the body. Ground-dwelling snakes, which only stand up in exceptional cases such as threatening behavior, comment fights and the like, have the heart after about the first third of their body length. This ensures the blood supply to the entire body and the snake is able to straighten its front third for a certain time. Sea snakes have their hearts roughly in the middle of their bodies. So they are able to take any position in their living space. If the snake is in an upright or inclined position, the formation of a blood congestion is delayed by the pressure of the water from outside, which supports the pumping capacity of the heart.
The esophagus is very curled, which makes it very flexible and allows large prey to be absorbed into the body. It should be noted here that the forked tongue does not play a role when swallowed, but only serves as a sensory organ (see chapter Sensory perception). The stomach is also elongated and has muscular walls. It produces the digestive enzymes and extremely strong digestive acids that attack everything except chitin (insect shell) and keratin (hair, feathers and claws); these are excreted with the faeces .
The testicles and ovaries are also elongated. The mating organ of the male snake is a paired hemipenis . Depending on the species, this is equipped with spines or thorns, which serve to get caught in the cloaca of the female snake during the act of mating . Due to the very different appearance of the hemipenis from species to species, it is an important determinant.
distribution
Snakes are common almost worldwide. Their habitats extend between about 66 ° north and 44 ° south latitude. No snakes have been observed outside of these latitudes. The furthest north living snake is the adder ( Vipera berus ), which is still found in northern Fennoscandinavia . The southernmost limit of distribution is Patagonia - this is where Cenicienta ( Bothrops ammodytoides ) is native. In many more remote regions there are no snakes, even within the latitudinal distribution limits. This applies to Ireland , Iceland , the Faroe Islands , the Azores , Bermuda , New Zealand and Hawaii , among others .
Habitats
In the course of their evolution , snakes were able to conquer a wide variety of habitats. Today we know of subterranean, terrestrial , aquatic (in both fresh and salt water ) and tree ( arborikol ) species. Some also represent mixed forms of the listed ways of life, such as semi-aquatic / semi-terrestrial. The more diverse a habitat is structured, the more resources and ecological niches it offers, the more snake species have been able to develop in it so far; By far the greatest biodiversity is therefore in the tropics, and many of the species living here are endemic . Even apparently hostile areas such as deserts or high mountains are populated.
Depending on their habitat, the snakes have different adaptations. These manifest themselves, for example, in the form of activity rhythms (winter rest in temperate zones, year-round activity in the tropical rainforest) or in sexual cycles of different lengths.
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Danger
Based on a long-term study in 2010, it was found that during the relatively short period of the study, 17 snake populations in Great Britain, France, Italy, Nigeria and Australia 11 have declined sharply. Something similar had previously only been observed in birds and amphibians . Complex causes are suspected, including deterioration in habitat status and the availability of prey. However, snake populations have also declined in protected areas where habitats are stable. Due to the correlation with climate data, global warming could be one of the causes. Because of the role of snakes as predators, a broad population decline would have a severe impact on many ecosystems.
Way of life
Snakes prefer a solitary way of life and have only weak social behavior . They only come together on special occasions, some are listed below:
- Mating (see also chapter reproduction )
- In places with high prey density (for example, it is typical for the garter snake ( Thamnophis sirtalis ) to visit places where the metamorphosis of amphibians takes place and where thousands of young frogs leave the water)
- At the egg-laying time in favorable breeding places (these are often limited in number, so several females usually lay their eggs at a suitable place at the same time)
- Creation of a favorable microclimate (for example with pregnant females to ensure optimal conditions for the offspring or to come together as so-called "winter societies" for wintering in the temperate zones)
Snakes only very rarely make territorial claims, such behavior is known in the Mambas ( Dendroaspis ) during the mating season. Many species are true to their location. In others one could observe migration behavior. This is partly due to the season (the change from the wintering place to the place of summer activity), partly due to population ecology (as soon as the population density increases too much in an area, the animals tend to diverge). For reasons not yet known, some snakes, typically desert dwellers such as the sidewinder rattlesnake ( Crotalus cerastes ), make seemingly arbitrary migrations over long distances.
Locomotion
Depending on their habitat, snakes use different modes of locomotion . So today all terrestrial snakes are able to crawl and swim; An exception are the snakes living underground, which mostly use the ditch. Sea snakes (Hydrophiinae) are very good at diving, closing their nostrils and staying underwater for up to an hour. Furthermore, some species are able to climb or jump. Some tree snakes ( chrysopelea ) can glide through the air by the other they flatten their bodies when jumping from a tree, giving them a kind even over short distances gliding possible. The crawling mentioned at the beginning is used by the vast majority of snakes. Due to the different soil situations, they use several techniques here:
- The Snake is the most common method. With its powerful muscles , the snake pushes itself forward obliquely from various objects such as stones and branches on the ground. Because it always pushes itself forward from both sides, the side forces compensate each other and a directed forward movement is created. In the jungle , snakes can move at a speed of up to 6 kilometers per hour.
- When crawling in a straight line, the snake moves through periodic waves of muscle contractions. This makes it possible to move forward in tubes and narrow crevices, albeit relatively slowly.
- During cross winds , the snake lifts its front body and pushes it back a little further to the side. At the same time, the other two to three points of contact with the ground move further towards the tail. In this type of locomotion, the snake only touches the ground with a small part of the body surface. Therefore it is mainly found in desert-dwelling snakes that have to move through loose sand.
- The accordion movement is encountered on smooth surfaces that offer little support and resistance. The snake draws its back part of its body and lays itself in tight loops. Then she stretches the front part of the body forward and pulls the rest back again.
Thermoregulation
Like all members of the reptile class, snakes are ectothermic . They are not able to keep their body temperature at a constant level through metabolic heat, but are dependent on an external heat supply. Warming up the body is essential because all functions are temperature-dependent. For example, digestion can only take place above a certain temperature (this varies from species to species). Movement can only take place when it is warmed up; at an outside temperature of 1 to 9 ° C, practically all species become immobile. However, this way of life also has advantages, because maintaining the body temperature in warm-blooded animals consumes a very large part of the food energy. Snakes therefore need less food and, depending on the type and size of the last meal, only have to hunt again every 2 to 10 days (small snakes) or every 4 to 10 weeks (large snakes).
Although the animals cannot generate their body heat on their own, they are able to regulate it to a certain extent. The body temperature is regulated to a level that is as constant as possible, which is in harmony with the optimal flow of all body functions. Because too much heat is just as dangerous as too little. At too high temperatures, for example, enzymes can denature and thus certain biochemical body functions can no longer be carried out, which can lead to death. There are various general thermoregulatory behaviors as well as special ones for warming up and cooling down.
- In general (keeping the temperature constant): By rolling up the snake achieves a reduction in the heat exchange surface, thus protecting itself against excessive heat loss and overheating at the same time. The animal is also able to widen and narrow its blood vessels, and at the same time it can lower or raise its blood pressure. In this way, it can control the release and absorption of heat. Snakes living underground regulate their body temperature via the level of the earth's layer in which they are located. If there is a risk of overheating, they dig deeper, if there is a risk of hypothermia, they dig further up.
- Warming: The most common and fastest method is sunbathing. Here, the snake exposes the largest possible body area to direct sunlight. Some species, for example the adder ( Vipera berus ), can even flatten their bodies and thus enlarge the irradiated area. Furthermore, the animals make use of the substrate heat conduction . They lie down on heated ground or stones that have a certain capacity for heat storage and at the same time are good heat conductors . In this way, twilight and nocturnal species extend their period of activity by repeatedly refueling with warmth in places with good heat conduction. In tropical regions, the temperature of the ambient air is usually sufficient to warm up. Here, in places with direct sunlight, it is usually too hot for the animals, they mainly use the cooling methods described below.
- Cooling: The simplest option is to seek out shade. If available, waters are also sought out. All snakes are able to swim and can use the cooling effect of the water. Here the opposite occurs to the heated stones, the snake gives off heat to the surrounding substrate . It has been observed that after particular physical exertion such as long hunting, flight, or a fight, snakes open their mouths and breathe heavily, which allows them to achieve a small degree of evaporative cooling . This is not possible through the skin, as is known from mammals , for example , since the animals do not have sweat glands. Desert snakes, on the other hand, have their own cooling method by digging into the sand.
Since sea snakes live in a completely different medium than terrestrial water, their thermoregulation possibilities are very limited. Air is a poor store of heat, but it is heated up relatively quickly. Water, on the other hand, is a very good heat store, but only heats up slowly. In some oceans it is always too cold, in others it is sometimes warm enough depending on the season and due to ocean currents. However, these are unsuitable as a habitat, as hibernation underwater is not possible. Sea snakes are therefore generally tied to warm regions.
Reproduction and development
pairing
Depending on their habitat, snakes reproduce all year round (for example in the tropical rainforest ) or only at certain mating times (in temperate zones, for example in spring after hibernation ). The mating season is determined by climatic influences, as the ectothermia of the animals influences all body functions from the outside temperatures; This also includes sperm and oogenesis .
The mating season is one of those conditions in which the otherwise solitary snakes actively seek out each other, with the activity always emanating from the males. The partner is tracked down by the sense of smell via the Jacobson organ . When the females move, they leave pheromones on the ground or in the vegetation, creating a scent trail that leads the males directly to them. At shorter distances, the visual sense also plays a role. As soon as another snake comes into view, it is determined whether it belongs to the same species and whether it is a male or a female.
If two males meet alone, they avoid each other. If, however, a female ready to mate is present at the same time, a ritualized commentary fight occurs, especially with the vipers , in which the male snakes wrap their bodies around each other, straighten their front thirds and then try to push each other to the ground. Such a fight takes place without biting attacks and injuries therefore practically do not occur. However, some species of adder tend to be more aggressive and do bite their opponents.
The victorious male then wraps around the female, pushes one of his two hemipenes into her cesspool and gets caught in it. The act of mating can last from ten minutes (some species of adder) to two days (some species of viper). Some species, such as the garter snakes ( Thamnophis ), can also be found peacefully in large clusters when mating, with many males snaking around a female trying to fertilize it. The picture that presents itself is called the “mating ball”.
Oviparity and ovoviviparity
Depending on the type of snake and the temperature of the habitat, embryonic development takes between two (for snakes native to the tropics) and five months (for ovoviviparous sea snakes). In general, the required incubation temperature is 25 to 30 ° C, although the development takes place faster within this range at a higher temperature. Therefore, depending on the habitat, fluctuations can occur within a species, such as the adder ( Vipera berus ), which occurs in warm Mediterranean regions as well as in northern Scandinavia. Most species of snakes (about 70%) are oviparous , only about a third are ovoviviparous (some adders, many vipers and sea snakes).
- Oviparium : Depending on the climatic conditions, oviparous species lay their eggs two to four months after fertilization in a well-protected, warm and humid place. They are always dependent on finding egg-laying places where optimal breeding conditions prevail, because the eggs laid are exposed to temperature and humidity fluctuations without protection. As a result, they are bound to milder climates. In most cases, existing niches (crevices, hollow tree trunks or the like) are used or new ones are created (pits in the ground). Some species show active brood care behavior , which is rather unusual for this animal order: some python species curl around their eggs and regulate the temperature of the clutch through muscle contraction; the spectacled snake ( well well ) stays near the clutch for several days after laying its eggs and actively defends its eggs against possible nest predators. After hatching, however, the young are largely on their own and are not looked after by their parents. When hatching, young animals have an egg tooth with which they can cut through the leather-like shell from the inside. They lose him within two days.
- Ovoviviparia : Depending on the climatic conditions, the young snakes are born two months at the earliest and five months at most after fertilization. They are born in a transparent shell from which they hatch during or immediately after the birth process. Compared to oviparity, one advantage of ovoviviparous reproduction is that the young snakes are almost immediately mobile and can flee from any danger. In addition, it is impossible for them to fall prey to robbers. Since the mother animals are able to a certain extent to regulate their body temperature, their body has a relatively constant temperature and humidity. Ovoviviparous species can therefore, in contrast to oviparous species, also colonize colder zones. In unfavorable years, mother snakes can delay birth into the warmer spring, which, however, represents an extraordinary physical burden for them and their young; mostly many young animals do not survive the winter in the womb and are born dead. Disadvantages of ovoviviparia are the mother's restricted mobility and increased energy requirements. It has to cover this with fat reserves, because there is no longer any space in the body for devoured prey. Some species, such as the meadow viper ( Vipera ursinii ), eat smaller prey such as insects during pregnancy.
The clutch size or litter size depends on the type and size of the mother and varies between 2 and 60, but is on average between 5 and 20 offspring.
Several species of snakes, including the flower pot snake and the North American copper head , have been shown to have the capability of obligatory or facultative parthenogenesis . In the case of a diamond rattlesnake , genetic markers were used to prove that it did not produce 19 offspring from fertilized egg cells until five years after the last contact with a conspecific.
Further development
Young animals resemble adults in their appearance, they are only smaller. The offspring of the venomous snakes are already equipped with a fully functional venom apparatus and are therefore capable of taking poisonous bites. Since more than half of all offspring often die in the first year and the mortality rate is still quite high for a few years afterwards, even in untouched nature, no more than 10 to 15% of offspring will probably reach adulthood.
Snakes can get different ages depending on their type and living conditions. Most of the time they live to a higher age in captivity, as there is no danger of predators and they receive veterinary care in the event of illness . The determination of the age in freedom brings with it certain problems, since today no possibility is known to determine its age on the basis of body characteristics of a living animal. Young animals cannot be marked externally, as the animals shed their skin very often and would also strip off any markings. Only a label that would be attached inside the body (for example a chip) could possibly bring such knowledge, but nothing has been mentioned in the literature about this to date. In dead animals, an approximate age can be determined using the bone structure (similar to the annual rings of a tree).
From the family of the giant snakes (Boidea) there are records of animals that have become over 40 years old, relating to the idol snake ( Boa constrictor ) and the ball python ( Python regius ). Representatives of the snake family can live to be over 30 years old, for example the corn snakes ( Pantherophis guttata , 32 years old). Vipers can live to be more than 20 years old, for example the Texas rattlesnake ( Crotalus atrox , 22 years old). The oldest known sea snake was a flattail ( Laticauda laticauda ) when it was five years old .
Chronobiology
Snakes also have different biological rhythms. In addition to irregularly recurring actions, such as the interval between food ingestions (this depends on the size of the last meal), there are also very regular processes determined by abiotic environmental factors. The two most pronounced are shown below.
Activity rhythms
Snakes are active at different times. The activity cycles are based on the one hand on climatic conditions and the thermoregulation needs of a snake, and on the other hand on the requirements of nutrition and reproduction. Furthermore, a distinction must be made between animals that are active during the day, at night and at dusk.
There are species whose circadian rhythm is determined exogenously , for example the aspis viper ( Vipera aspis ), which is diurnal in spring and autumn, and is also crepuscular in summer and sometimes even nocturnal. In contrast, there are species in which the rhythm is endogenously determined, such as the adder ( Vipera berus ), which is basically only diurnal, or the Girondas smooth snake ( Coronella girondica ), which is only active at dawn.
In temperate zones, snakes are only active during the warmer seasons. They spend the winter in frost-free hiding places in a frozen state . During this time only life-sustaining processes take place in the body and these are also reduced to the necessary minimum. They get energy for this from their fat reserves that they have accumulated in summer. Snakes also reduce their energy costs during long periods of rest by making certain organs such as the intestines, lungs, heart and kidneys smaller. This is possible because their metabolism is greatly reduced during the freezing winter. If the temperatures rise again, the metabolic rate of the animals increases and they wake up; Males usually about two weeks before the females.
Sexual cycles
The time span of the sexual cycle of different snake species is determined by the climate of their habitat. For the oogenesis that spermatogenesis and, ultimately, to the development of embryos certain temperatures are required. Accordingly, the duration of a cycle ranges from a few months to two years.
- Cycle in cool temperate climates: The activity phase of snakes in this climate is too short for the entire reproductive cycle to take place within a year. Most cycle year takes place in the first instance in April or May the female the vitellogenesis (yolk formation), the male spermatogenesis. The yolks or pre-sperm are stored in the body over the winter. In the following spring, the male completes its hibernation about two weeks before the female so that the sperm maturation is completed by the mating season. Then the female ovulates and fertilization can take place. Usually the mating season is in April or May, so there is enough warmth for embryonic development over the summer. But it can also happen that in cold years mating does not take place until autumn and the females take the zygotes with them into the winter. Their growth does not begin until next spring.
- Cycle in a warm, temperate climate: In most cases, this can be referred to as a circannual (approximately annual) rhythm. Spermatogenesis and vitellogenesis take place immediately after the end of hibernation (around the end of February to the beginning of March), around the end of May the sperm are ripe and the females are ready to mate. The young snakes are born or hatch at the end of July or beginning of August, some oviparous species even lay eggs twice in very warm and productive years.
- Cycle in subtropical climates: In these climates, the temperature plays less of a role than the humidity. During the dry season (spring and winter) this is not available to the extent that it is necessary for the young snakes to develop properly. After hatching or birth, these are dependent on regulating their water balance. In the dry season they can neither drink nor eat prey (since neither is available or only to a small extent). The mortality rate would be too high for the species to survive. Therefore, only vitello and spermatogenesis take place in the dry season, the hatching or the birth of the young takes place in the rainy season , i.e. in summer and autumn. Some oviparous species lay eggs several times a year.
- Cycle in the tropical climate of the equatorial regions: There is no fixed time of reproduction and no specific mating season. Temperatures and humidity levels are relatively constant all year round. Accordingly, the snakes do not reproduce here at set times, after one cycle the next can begin again immediately.
threat
Snakes have different threatening behaviors . As with many other animals, it involves making oneself appear taller. To do this, the animals erect their front thirds in an S-shape and roll the rest of the body underneath. Some species keep their body part rolled up in constant, wave-like motion, others also spread their neck area, such as the cobras ( Naja ), or inflate it, such as the African tree snake ( Dispholidus typus ). It has been observed that non-toxic representatives in particular greatly exaggerate the threatening gesture of appearing larger. This is supposed to intimidate the opponent so much that he doesn't even attack. Should he do so, the snake has no weapon that could be dangerous to him; therefore she tries to prevent.
It is also known that many species use certain noises to threaten themselves. These include hissing, hissing or rattling. The latter is caused by rubbing keeled scales against each other, as in the sand rattle otters ( Echis ), or by vibration of the tail. Either this generates the noises using aids such as dry grass, or the noise is generated with a tail rattle made of keeled, overlapping horn rings like those found in rattlesnakes . There are also species, such as the Arizona coral snake ( Micruroides euryxanthus ), the noisy air through their cloaca email, sometimes accompanied by excrement , the smell to deter the enemy. Sham bites are also part of the behavioral repertoire; Poisonous snakes do not emit any poison because it would be wasted and would have to be synthesized again.
defense
If threats fail, snakes also have various active and passive defense strategies.
Both poisonous and non-poisonous representatives bite for defense, whereby the poisonous usually achieve a stronger effect, because in contrast to the sham bites, poison is definitely given off in the defensive bite. In many non-toxic species, such as pythons , the sharp teeth break off and remain in the opponent's wound, which can lead to painful inflammation . This does not mean a great loss for the snake, as the teeth grow back quite quickly (see chapter Teeth ).
Some species such as the red spitting cobra ( Naja pallida ) inject their venom from their mouths several meters away. They always try to meet the opponent's eyes. Depending on the type and strength of the poison, a victim can become temporarily or even permanently blind . The tiger snake ( Rhabdophis tigrinus ) has developed a very special defense : it is not able to synthesize poison on its own, but eats poisonous toads and stores their poison in a special reservoir on the neck. If she gets into trouble, she sprays the collected toad poison in the direction of the enemy.
In addition to biting and lethal injection, several passive defense strategies are known. Fast vipers rely on their speed and flee, while more sluggish vipers often rely on their camouflage . Non-poisonous species sometimes intentionally reproduce the conspicuous coloration of poisonous species in order to demonstrate an alleged danger ( mimicry ), for example the non-poisonous triangular snake ( Lampropeltis triangulum ) looks very similar to the highly poisonous representatives of the coral snake ( Micrurus ). In the grass snake ( Natrix natrix ), it was observed that they totstellt itself which is unusual for this group of animals. The animal turns on its back, opens its mouth and lets its tongue hang out. Some observations even report that saliva flows out of the mouth , mixed with some blood . This is supposed to make the deception perfect. Some species, such as the ball python ( Python regius ) roll along their entire body, the head is held centrally (hence the nickname "Ball Python"). The tail end is presented to the opponent as a dummy head . If he attacks there, the snake is only injured on a non-vital part of the body. Mostly she can then use the confusion of the enemy to flee.
Furthermore, many snakes use the opportunity to secrete a smelly secretion from their anal glands . This creates a smell of putrefaction and drives away the interest of most opponents, as they do not feed on carrion .
nutrition
All snakes are predators and feed on other, live or recently killed animals. Their range of prey animals is determined by their body size and the offerings in the respective habitat. Accordingly, smaller snakes mainly eat insects . Medium-sized snakes will eat rodents , frogs, and lizards , and sometimes birds , eggs, and other snakes. The food spectrum of large snakes includes everything from rabbit-sized mammals to deer or wild boar . Insects and other smaller prey (e.g. amphibians) are usually swallowed alive, larger ones are killed before being eaten.
Because of the range of prey determined by body size, that of young snakes often differs from that of adult snakes. The Terciopelo lance viper ( Bothrops asper ), for example, eats small lizards and arthropods as young (around 25 centimeters long), and small mammals and birds as an adult snake (150 centimeters or more). This is a great advantage, because adult and young animals occupy different ecological niches and are therefore not in competition with one another.
With regard to the food spectrum, there are distinct specialists as well as opportunists among snakes . Some examples are given below.
- Specialists: Representatives of the thick-headed snakes (Dipsas) only eat snails. They are equipped with a hook-shaped, elongated lower jaw, with which the snails can be released from their housing and levered out. Another example are the African and Indian egg snakes (Dasypeltis and Elachistodon). They only eat bird eggs. These are completely devoured. The shell is destroyed shortly after the slinging process by means of small, elongated cervical vertebral processes (hypapophyses). The yolk and egg white are transported into the stomach and the shell is choked out.
- Opportunists: These include all giant snakes above a certain size. At 10 meters in length, pythons weigh around 100 kilograms and are therefore able to kill almost any other animal. These animals are only limited in their food intake by the widening of the mouth opening and the flexibility of their bodies: only prey animals that do not exceed a certain size can be swallowed. Another opportunist is the water moccasin snake ( Agkistrodon piscivorus ). It is the only species known to even eat carrion at times .
Regarding the frequency of food intake, it can generally be said that females are more voracious than males, as they have to use a lot of energy for yolk formation. However, they are very cautious when they are pregnant and shortly before oviposition (see chapter on reproduction). It has also been observed that there is no more food intake from around two weeks before moulting. Smaller species and young animals eat more often, due to a higher metabolic rate than larger species or adults . Snakes can ingest enormous amounts in relation to their own body mass (vipers can devour prey up to about 36%, other snakes up to about 18% of their own mass). If the snake succeeds in catching such a large prey, the next food intake usually takes place weeks later (the estimated annual food requirement of an adult adder ( Vipera berus ) is around 350 kcal , which corresponds to around 10 voles). Giant snakes (Boidae) can starve for over a year.
Food intake is also temperature dependent. Below 10 ° C there is no digestion in the ectothermic animals (see chapter Thermoregulation ). If a snake has devoured its prey and then the ambient temperature drops below 10 ° C, it chokes its meal again. This is necessary because as soon as digestion stops due to the too low temperature, putrefaction begins. This would produce poisons (for example the gases ammonia and hydrogen sulfide , or propionic and acetic acid ), which could lead to the death of the snake. The highest degree of effectiveness of digestive enzymes is, depending on the type, around 30 ° C.
hunt
Snakes use two main hunting methods, these are ambushing (for example, many vipers hunt ) and hunting (many snakes ).
The ambulance hunters rely on their camouflage for their hunting method and wait until a prey comes close enough to them. Then they come up against the prey very quickly (up to 10 meters per second) and bite it. The further course depends on which snake family the hunter belongs to: the representative equipped with poisonous teeth lets go of the prey again. The latter flees and the snake, in the certainty of the effects of its poison, sets out in pursuit. To do this, it uses its nasovomeral sense and follows the scent trail of the prey. This succumbs after a short time, usually after a few minutes, to the injected poison and dies. As soon as the snake gets to its victim, it devours it.
The non-poisonous ambulance hunter, on the other hand, bites his prey and wraps his own body, especially the chest, around it. With each exhalation of the prey, the snake tightens until the victim loses consciousness. However, the snake holds on until its heart has stopped beating. After death has occurred, the serpent can begin to eat.
A few snakes also use completely different hunting and killing methods. For example, tree-dwelling ( arborikole ) representatives, such as the liana snake ( Thelotornis kirtlandii ), let their front part dangle over the forest floor, while they hold onto the branches with the rest of their bodies. Due to their shape and color, they look like a creeper and are not perceived as a danger by passing animals. If an animal that fits the range of prey of the respective snake comes by, it simply snaps to. Other tree dwellers, such as the Mambas ( Dendroaspis ), observe the forest floor from a height and let themselves fall on suitable prey.
Small and subterranean snakes devour their prey, mostly insects, alive immediately after being caught.
The looping process follows a certain pattern. Prey animals are generally devoured in one piece (see also the chapter on anatomy ). Anura (Anura) and smaller prey are eaten by any particular scheme. Hairy prey animals or birds, however, are always preceded consumed with the head, so that their fur or feathers should not prepare the Down slings and hinders Schlingvorgang. What is important here is the mobility of the lower jaw bones to one another and to the toothed bones of the roof of the mouth. By alternating movements of these bones towards each other, the prey is transported further and further into the gullet. The tips of the teeth, which are strongly curved backwards (towards the throat), are helpful. From the throat, the spine takes on the further transport by means of wave-like movements. As soon as it is able to, the snake stretches the front part of its body upwards in order to use gravity to support the looping process. When the prey is completely devoured, the snake sorts its skull bones by yawning several times. During devouring, the snake is at the mercy of its enemies, so it strangles the prey again when disturbed.
Snake venom
Venomous snakes use their venom mainly to hunt prey, but also for defense. Snake poisons consist of various proteins and are viscous and have a milky-white to yellowish color. Depending on the type, the poison affects the nervous system ( neurotoxins ), the blood cells and vessels ( hemotoxins ), the heart ( cardiotoxins ), the tissues or the coagulation ( coagulants ) or at several of the above-mentioned sites of action. Around 600 species of snakes are poisonous and of these around 50 are potentially fatal to humans. There is no reliable information on the number of deaths caused by poisonous snakes worldwide each year; a more recent estimate gives 21,000 to 94,000 deaths per year. In medicine, snake poisons and products derived from them are used both to treat diseases and to research new active substances. They also serve as a starting material for the manufacture of antidotes.
Natural enemies
Snakes are involved in predator-prey relationships in a variety of ways . They are both predators and prey. Groups of creatures that can pose a threat to snakes are described below.
- Mammals: Although no mammal specializes in snake hunting, some seem to be part of the usual food spectrum. Here it is mainly big cats such as the leopard . This can kill pythons up to four meters long (although the python can kill the leopard as well). Even small felids occasionally prey on snakes corresponding to their size. A particularly well-known enemy from the feline group is the mongoose , which, when fighting a cobra, exposes itself to a low risk of being bitten due to its speed and thick fur. However, it is not resistant to their poison. Representatives from the marten family are also natural enemies. Primates and pigs occasionally prey on and eat snakes, the latter being protected to a certain extent from possible poisonous effects by their thick bacon rind. The ungulates should also be listed here not directly as enemies, but as a threat in certain situations . These occasionally trample on snakes, either unintentionally or when they see their young threatened by them.
- Birds: The most snake-eating birds around the world are birds of prey . These grab the snake by the neck and break its spine with one jerk. Toed eagle who specializes in snake hunting, as well as the Secretary , who chases the snake over and kills them with targeted kicks to the head and the neck. Occasionally waders (such as storks or herons ), ravens , cuckoos and rheas feed on snakes. Chicken birds, on the other hand, are particularly dangerous for small and young snakes . The small snakes pose no threat to them and therefore fit exactly into their prey spectrum.
- Reptiles, amphibians, fish: snakes fall prey to alligators , crocodiles or larger turtles such as the North American snapping turtle ( Chelydra serpentina ) in water . On land, larger lizards such as monitor lizards can be dangerous to them. Although amphibians do not specifically hunt snakes, small specimens in particular are occasionally eaten by larger toads and frogs . Carnivorous fish of various groups such as pike and shark can also prey on snakes.
- Other snakes: Some species such as the collar snake ( Diadophis punctatus ) or the smooth snake ( Coronella austriaca ) do not have a set food spectrum. They eat anything that corresponds to the size of their prey range, including other species of snakes. Other genera, such as the American king snake ( Lampropeltis ) or the Asian king cobra ( Ophiophagus ), on the other hand, have specialized in hunting other species of snakes. Cannibalism also occurs, but has been observed more frequently in captivity than in the wild. Often the adults eat the juveniles . The scarlet snake ( Cemophora coccinea ) almost exclusively eats snake eggs .
- Invertebrates: Arachnids such as scorpions , roller spiders , large spiders and large millipedes occasionally eat very small snakes. Hibernating snakes are also occasionally eaten by representatives of some species of spiders, tapers or ground beetles . Slow or immobile snakes (such as pythons that have to pause due to a digestive pause) can even be prey to ants .
Diseases
Under normal conditions, snakes are relatively insensitive to pathogens. In the event of physiological changes (moulting, overwintering, etc.) or changed environmental conditions or a changed microclimate, the normal flora spectrum (here the fungal and bacterial flora ) can change in favor of pathogenic fungi and bacteria: For example, snakes are very sensitive to cold and can under get pneumonia or digestive disorders in cold conditions. Wound infections and skin abscesses can also be more common. If a prey defends itself against devouring and injures the snake's mouth, this can lead to stomatitis , a serious infection of the oral cavity that can be fatal. In addition, snakes can be infected by various parasites , such as B. mites , ticks or roundworms be infested.
Fungal diseases ( mycoses ) in snakes mainly affect the skin. A fungus from the Onygenaceae family , Ophidiomyces ophiodiicola , is increasingly manifesting itself as the pathogen that seems to be responsible for a large part of the skin mycoses in snakes of different families . This fungal disease was observed increasingly in North America and in 2017 the fungus was also detected in wild snakes in Europe. The clinical picture can be very variable, but in some cases it leads to the death of the affected animal. Decisive factors seem to be on the one hand the health of snakes and on the other hand environmental conditions (e.g. milder and wetter winters as a result of climate change ). So far, little is known about the fungus, its distribution and its importance for snakes, but it is assumed that in principle all types of snakes could be susceptible to the fungus.
Evolution and systematics
Tribal history
The oldest snake fossil finds come from the Middle Jurassic, Upper Jurassic and Lower Cretaceous. These are Eophis underwoodi from the Bathonian (about 167 million years ago) of England, Portugalophis lignites from the Kimmeridgian (157 to 152 million years) of Portugal, Diablophis gilmorei from North America (also from the Kimmeridgian) and Parviraptor estesi from the Berriasium (145 to 140 million years ago) of England. All of them still had four small legs, but some of them already showed the typical snake skull. Other Mesozoic snakes have been dated to about 95 to 100 million years ago in the Upper Cretaceous ; they were already very similar to today's snakes. These are various skeletal fragments of the species Laparentophis defrennei from Algeria, Coniophis precedens from the North American Lance Formation , and Pachyrhachis problematicus in the Middle East. With the latter one is not yet sure whether it is a snake species or a monitor lizard with reduced extremities.
Possible ancestors are today lizards , probably early Waranartige (Varanomorpha) suspects. The reason for this assumption is the similarly structured skull, in particular the structure of the lower jaw, the split tongue and the type of tooth change , which for example resembles that of the crusty lizard ( Heloderma ). Added to this is the common reduction of the left lung and the development of a Jacobson organ .
All fossil varanids known today lived in water and some of them also lived in the sea. Especially the mosasaurs , a group of marine , monitor-like lizards from the late Cretaceous with their extremities receded into fins, as well as pachyophis from today's Bosnia-Herzegovina and pachyrhachis from the Middle East are classified as the ancestors of snakes. The theory that these aquatic monitor lizards were supposed to be direct ancestors of snakes has been abandoned in favor of a theory that they are more likely to be derived from forms burrowing in the ground. As evidence especially the grave lifestyle of the most original of living today Schlangentaxa who are blindsnakes , and the snake-like shape at convergent without limbs evolved vertebrate groups with grave forming activity as the Sneak amphibians (Gymnophiona) within the amphibians and crawl and amphisbaenians specified within the lizards.
The currently favored theory is that the first half snakes grave border and halbaquatile reptiles were living in mud, similar to the recent Earless Monitor ( Lanthanotus borneensis ). The burrowing way of life in this substrate is believed to be the reason that snakes have reduced their extremities that are not needed in this habitat . The slim, smooth body is an ideal adaptation to life underground, as the animals do not get caught and can move relatively quickly. Digging was done with the head or a reinforced and specially shaped rostral shield , as is the case with recent sand boas (Erycinae) or blind snakes such as the idiot ( Typhlops vermicularis ) still doing today. Like all snakes, these have modified head scales, a reinforced skullcap and specific adhesions and reductions in the head skeleton, which increase the stability when digging.
External system
The classification of the snakes within the scale reptiles has not yet been fully clarified. In traditional taxonomy the snakes are classified as a separate suborder next to the lizards (Lacertilia), but this is rejected by more recent considerations within phylogenetics . It now seems fairly certain that the queues together with the Waranartigen (Varanomorpha) a taxon form and the sister group of the extant species of lizards ( Varanoidea represented) or may even out as Pythonomorpha within the Waranartigen as a sister group of lizards. Monitor lizards and snakes are in turn grouped together with the sneak (Anguidae) and hump lizard (Xenosauridae) to form the sneak-like (Anguimorpha).
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The classic subordination of the lizards is to be regarded accordingly in relation to the snakes as a form taxon or paraphyletic group , while the snakes themselves form a natural group ( monophyletic taxon ).
Internal system
Osteological investigations of fossil and recent taxa showed that today's snakes fall into two major lines: The blind snake-like (Scolecophidia) on the one hand and the real snake (Alethinophidia) on the other. As far as we know today, around 3,000 different species of snakes are known. Many of them disagree as to whether they should be recognized as a subspecies or as a separate species , and new species are regularly discovered. For these reasons, the number given in the literature differs very strongly in some cases. Regular revisions also lead to changes within the individual taxa, which leads to further differences in the literature.
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Phylogenetic systematics of snakes according to Pyron et al. 2013
The systematics according to the Reptile Database is shown below :
- Superfamily Acrochordoidea
- Wart snakes family (Acrochordidae)
- Superfamily Uropeltoidea s. l.
- Family root snakes (Anomochilidae)
- Family roller snakes (Cylindrophiidae)
- Family tails (Uropeltidae)
- Superfamily Pythonoidea s. l.
- Pointed-head pythons family (Loxocemidae)
- Python family (Pythonidae)
- Family Xenopeltidae
- Superfamily Booidea
- Boas family (Boidae)
- Subfamily Boaschlangen (Boinae)
- Subfamily earth pythons (Calabariinae)
- Subfamily Pacific Boas (Candoiinae)
- Subfamily dwarf boas (Charininae)
- Subfamily sand boas (Erycinae)
- Subfamily Madagascar boas (Sanziniinae)
- Boas family (Boidae)
- Superfamily adder-like and viper-like (Colubroidea)
- Adder family (Colubridae)
- Subfamily real snakes (Colubrinae)
- Subfamily Grayiinae
- Subfamily Calamarinae
- Subfamily Dipsadinae Bonaparte 1840
- Subfamily Pseudoxenodontinae McDowell 1987
- Subfamily Natricinae Bonaparte 1840
- Subfamily Scaphiodontophiinae
- Family Lamprophiidae Fitzinger 1843
- Subfamily Aparallactinae
- Subfamily Erdvipern (Atractaspidinae Günther 1858)
- Subfamily Lamprophiinae Fitzinger 1843
- Subfamily Psammophiinae Bonaparte 1845
- Subfamily Prosymninae
- Subfamily Pseudaspidinae
- Subfamily Pseudoxyrhophiinae Dowling 1975
- Snake family (Elapidae)
- Subfamily true poisonous snakes (Elapinae)
- Subfamily sea snakes and Australo-Asian poisonous snakes (Hydrophiinae)
- Family snakes (Homalopsidae Bonaparte 1845)
- Family Pareidae Romer 1956
- Viper family (Viperidae)
- Subfamily Fea vipers (Azemiopinae)
- Subfamily pit vipers (Crotalinae)
- Subfamily Real Vipers (Viperinae)
- Mute snakes family (Xenodermatidae Gray 1849)
- Adder family (Colubridae)
- Superfamily blind snakes (Typhlopoidea / Scolecophidia)
- American blind snakes (Anomalepidae)
- Gerrhopilidae
- Blind snakes (Typhlopidae)
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Slender blind snakes (Leptotyphlopidae)
- Subfamily Leptotyphlopinae
- Subfamily Epictinae
- Xenotyphlopidae
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incertae sedis
- Family roller snakes (Aniliidae)
- Family bolyeriidae (Bolyeriidae)
- Erdboas family (Tropidophiidae)
- Family Xenophidiidae
Symbolism and mythology
The letter S is a symbol of the snake both because of its shape and because of the sibilant sound.
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Egypt
In pre-dynastic Egypt , the snake goddess Wadjet was worshiped. Their symbol was the Uraeus . Furthermore, the ancient Egyptians knew Mehen , a snake god who protected the sun god Re during his night journey through the underworld. Belief in the god Apophis has also been documented since the Middle Kingdom . The god depicted as a giant snake was the embodiment of dissolution, darkness and chaos and at the same time the great adversary of the sun god Re.
middle East
In the Middle East , in the Levant , in the area of the Golden Crescent , in the Mycenaean culture and many other cultural areas of Western Asia, snake cults were of great importance in the Epipalaeolithic and Neolithic . Each deity was associated with snake representations, especially on reliefs and ceramics.
Bible
It is generally believed that the serpent in the Bible is largely a symbol of the devil. In the story of Paradise ( Genesis 3) the serpent is a symbol of temptation and seduction to evil; it arouses doubts about God's goodness and seduces Eve to eat from the "tree of the knowledge of good and evil". Martin Luther translates the Hebrew word da'at as “knowledge” in the sense of “omniscience”: man wants to be like God and makes himself lord over “good and bad”, that is, over everything. In some Gnostic sects Eve and the serpent were worshiped for the knowledge made available to the people (although there she was sometimes depicted as Eve's male companion, Ophion ).
As the people of Israel wander through the desert, snakes plague them ( Numbers 21); Moses is to raise up a brazen serpent , and whoever looks up to it is to be saved. Here the snake appears (like the cross for Christians) as a sign of salvation. In 2. Book of Kings 18: 4 it is reported that this brazen serpent, known as "Nehushtan", was kept until the time of King Hezekiah ; but because it was worshiped, it was smashed by Hezekiah.
Even if Jesus recommends to his disciples: “Be wise as the serpents and without falsehood like the doves!” ( Matthew 10:16), in the book of Revelation the serpent still clearly remains an image of evil: “And he took hold of the dragon , the ancient serpent who is the devil and Satan ”( Revelation of John 20: 2).
India
In Indian folklore, the snake goddess Manasa is revered, who protects people from poisonous snakes. In the Indian creation myths there is the snake king Ananta-Shesha , who rests on the bottom of the primeval ocean between two world ages. Under the name Vasuki, the same serpent king helps whisk the ocean of milk to obtain the immortality potion. The poisonous snake Kaliya is defeated by Krishna , who plays the flute while dancing on their severed heads. On the occasion of this victory, Krishna is celebrated for several days every year. Milk and rice offerings are offered at the temples for the snakes, which are a symbol of life energy, and the snake charmers who blow on their pungi receive alms.
China
In China , the snake was a symbol of cunning, malice and deceit. It is one of the five poisonous animals . It is found as the 6th sign 蛇 , shé in the twelve branches of the earth .
Ancient Greece
In ancient Greece , the snake was considered sacred. Since it could renew itself infinitely often through the regular moulting in the eyes of the people, it was thought to be immortal. From the human point of view, this act of rejuvenation and the fact that the snakes were promised healing powers ultimately made the snake a symbol of the medical profession. To this day it has kept itself in the sign of the Aesculapian staff, which is also, greatly simplified, found today in some pharmacy signs . The snake was also said to have clairvoyance, which is why it was one of the animals of the goddess Gaia . According to Hesiod , Gaia Pelope was one of the many names of the earth goddess Gaia. In the oracle of Delphi , female priests ( Pythea ) did their job . Not only in the Judeo-Christian tradition there was a tree guarded by a snake: in the ancient Greek imagination, the life-giving apple tree , which was given to the goddess Hera by Gaia and was guarded by the serpent Ladon , stood in the garden of the Hesperides .
Italy
In Italy the Martians tribe were known as snake worshipers and snake tamers. Angitia, the goddess of snakes and poisons, was worshiped by them 3000 years ago. A snake procession (“la festa dei serpari”) in honor of Dominic of Sora still takes place in the small town of Cocullo in Abruzzo at the beginning of May . Numerous live snakes surround the wooden figure of the saint.
Northern Europe
In Germanic mythology that plays Midgardschlange that spans the world, but also the race of gods of the Aesir , threatened an important role.
In the pagan religion of the Balts , snakes, like toads, played a significant role. Each family was lucky when a grass snake in the fireplace, in the bath house or under the hand mill settled. She was fed eggs and milk like a pet and carefully observed whether she accepted the food. For Lithuania, snake charmers, zaltones (lit. žaltys » grass snake «) have been handed down.
North and Central America
Among the North American Indians , the rattlesnakes ( Crotalus ) play an important role in myth, legend, religion and folk art. Some tribes feared them as bringing disaster; many tribes did not kill rattlesnakes. It was believed that the number of rings on the tail rattle indicated the number of victims killed. The Hopi Indians regard the rattlesnakes as messengers of the gods and use them in a rain summoning ritual, the best-known Native American ceremony of the snake dance . With the Cahuilla , no bitten person was allowed to come close to a pregnant woman; a bitten pregnant woman allegedly gave birth to a child with a (naturally invisible) snake skin. The tail rattles were often used as amulets , and arrowheads were impregnated with the poison of the rattlesnakes.
In some Central American cultures , the Ouroboros is now a living deity . The archetypal motif Ouroboros is often depicted with one or two snakes biting their tails and symbolizes infinity .
Australia
The rainbow serpent in the myths of the Australian embodies Aborigines the primal state of nature in a state of dream time and have dominion over their equally life-giving and devouring aspects, in particular, they guarded the water.
literature
- Roland Bauchot (Ed.): Snakes. Naturbuch Verlag, Augsburg 1994, ISBN 3-89440-075-7 .
- Wolfgang Böhme : Amniota, umbilical animals. In: W. Westheide, R. Rieger: Special Zoology. Part 2: vertebrates or skulls. Spektrum, Munich 2004, ISBN 3-8274-0307-3 .
- Wolfgang Böhme et al .: Handbook of the reptiles and amphibians of Europe. Volume 3 / IIB, Snakes (Serpentes) III. AULA Verlag GmbH, Wiebelsheim, ISBN 3-89104-617-0 .
- Ulrich Gruber: The snakes in Europe and around the Mediterranean. Franck'sche Verlagsbuchhandlung, Stuttgart 1989, ISBN 3-440-05753-4 .
- Nicholas R. Longrich, Bhart-Anjan S. Bhullar, Jacques A. Gauthier: A Transitional Snake from the Late Cretaceous Period of North America. In: Nature . 2012. doi: 10.1038 / nature11227 , pp. 1-4.
- Chris Mattison: The Snake Encyclopedia. BLV Verlagsgesellschaft mbH, Munich 1999, ISBN 3-405-15497-9 .
- Mark O'Shea: Venomous snakes. All species in the world in their habitats. Franckh-Kosmos Verlag, Stuttgart 2006, ISBN 3-440-10619-5 .
Individual evidence
- ^ Species Numbers. In: reptile-database. January 2018, accessed January 17, 2018 .
- ↑ GM Fredriksson: Predation on Sun Bears by Reticulated Python in East Kalimantan, Indonesian Borneo . Raffles Bulletin of Zoology 53 (1), 2005, pp. 165-168, pdf .
- ↑ Illustrations of the different teeth. In: Reptiles du monde. Archived from the original on January 21, 2012 ; Retrieved April 1, 2013 .
- ↑ a b Kurt Schwenk: Why snakes gave forked tongues In: Science Volume 263, March 18, 1994, pp. 1573-1577, doi: 10.1126 / science.263.5153.1573 .
- ↑ Why do snakes have forked tongues? ( Memento of the original from October 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Paul Friedel, Bruce A. Young, J. Leo van Hemmen: Auditory localization of ground-borne vibrations in snakes. Physical Review Letters 100, 048701 (2008), doi: 10.1103 / PhysRevLett.100.048701
- ^ LD Brongersma: On the main branches of the pulmonary artery in some Viperidae . In: Bijdragen tot de Dierkunde , Vol. 28, No. 1, 1949, pp. 57-64 (PDF) .
- ↑ LD Brongersma: Some remarks on the pulmonary artery in snakes with two lungs . In: Zoological Negotiations , Vol. 14, No. 1, 1951, pp. 1–36 (PDF) .
- ↑ Roger S. Seymour, Harvey B. Lillywhite: Blood pressure in snakes from different habitats , Nature, Volume 264, Issue 5587, pp. 664-666, December 16, 1976, doi: 10.1038 / 264664a0
- ^ Andrew Durso: Are there any countries without snakes? Entry from October 3, 2015 on the serpentological blog Life is short but snakes are long. (accessed on February 8, 2016)
- ↑ Chris Reading et al .: Are snake populations in widespread decline? Biology Letters, June 9, 2010, doi: 10.1098 / rsbl.2010.0373
- ^ Warren Booth, Gordon W. Schuett: Molecular genetic evidence for alternative reproductive strategies in North American pitvipers (Serpentes: Viperidae): long-term sperm storage and facultative parthenogenesis. In: Biological Journal of the Linnean Society , Volume 104, No. 4, 2011, pp. 934-942, doi: 10.1111 / j.1095-8312.2011.01782.x
- ↑ Age list of various types of snakes
- ↑ Christopher McGowan: The Raptor and the Lamb - Predators and Prey in the Living World. Penguin Books, London 1998, ISBN 0-14-027264-X , pp. 52 and 53
- ↑ Anuradhani Kasturiratne, A. Rajitha Wickremasinghe, Nilanthi de Silva, N. Kithsiri Gunawardena, Arunasalam Pathmeswaran1, Ranjan Premaratna, Lorenzo Savioli, David G. Lalloo, H. Janaka de Silva: The Global Burden of Snakebite: A Literature Analysis and Modeling Based on Regional Estimates of Envenoming and Deaths. PLoS Medicine . Volume 5, No. 11, e218 doi: 10.1371 / journal.pmed.0050218 .
- ↑ a b Philipp Berg: A snake mushroom on the advance in North America and Europe . In: Terraria / Elaphe . No. 69 , 2018, ISSN 1613-1398 , p. 70-77 .
- ↑ Lydia HV Franklinos, Jeffrey M. Lorch, Elizabeth Bohuski, Julia Rodriguez-Ramos Fernandez, Owen N. Wright: Emerging fungal pathogen Ophidiomyces ophiodiicola in wild European snakes . In: Scientific Reports . tape 7 , no. 1 , June 19, 2017, ISSN 2045-2322 , doi : 10.1038 / s41598-017-03352-1 ( nature.com [accessed May 30, 2018]).
- ↑ The fungus Ophidiomyces ophiodiicola in snakes in Europe. Retrieved May 30, 2018 .
- ↑ Michael W. Caldwell et al. 2015. The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature Communications 6, article number: 5996; doi: 10.1038 / ncomms6996
- ↑ Among others in Wolfgang Böhme 2004
- ↑ Böhme 2004, Mikkos Phylogenetic Archive: Platynota ( Memento of the original from June 4, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Nicholas R. Longrich, Bhart-Anjan S. Bhullar, Jacques A. Gauthier: A Transitional Snake from the Late Cretaceous Period of North America. In: Nature , 2012. doi: 10.1038 / nature11227 , p. 3.
- ↑ Example of the discovery of a new species of snake ( memento of the original from January 17, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Robert Alexander Pyron, Frank T. Burbrink & John J. Wiens: A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 2013, 13:93 doi: 10.1186 / 1471-2148-13-93
- ↑ The Reptile Database: Suborder Ophidia (Serpentes) - Snakes
- ↑ Dimitra Rousioti: Did the Mycenaeans believe in theriomorphic divionities? POTNIA. Deities and religion in the Aegean Bronze Age. Proceedings of the 8th International Aegean Conference. In: R. Laffineur, R. Hagg (eds.), Aegaeum 22, 2001, pp. 305-314.
- ↑ Birgit Kahler: Snake worship in the early history of Mesopotamia. In: Mysteria3000 . Issue 24/25, ISSN 1619-5744 / ISSN 1619-5752 .
- ^ Diana Krumholz McDonald: The serpent as healer: theriac and ancient Near Eastern pottery. In: Source. Notes in the History of Art Volume 13, No. 4, 1994, pp. 21-27.
- ↑ James H. Charlesworth: The good and evil serpent: How a universal symbol became Christianized. Anchor Yale Bible Reference Library, Yale University Press, New Haven 2010, ISBN 978-0-300-14082-8 .
- ↑ Dimitri Nakassis, Joann Gulizio, Sarah A. James: KE-RA-ME-JA "In: Prehistory Monographs Volume 46, 2014.
- ↑ The snakes of St. Dominic
