Water moccasin otter
| Water moccasin otter | ||||||||||||
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Water moccasin otter ( Agkistrodon piscivorus ) |
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| Agkistrodon piscivorus | ||||||||||||
| ( Lacépède , 1789) |
The water moccasin viper ( Agkistrodon piscivorus ) is a species of snake that is widespread in the southeastern United States and occurs in three subspecies. It belongs to the subfamily of pit vipers . It is also sometimes referred to as a water moccasin snake. The species is closely tied to all kinds of standing water, where it preyes on all small vertebrates that occur there , as well as various invertebrates and occasionally eats carrion . Like all pit vipers, the water moccasin viper is poisonous, but the bite is rarely fatal to humans.
description
Water moccasin otters are stocky and sturdy. The body length varies greatly and is usually between 75 and 155 cm, the largest specimens can be 185 cm long. The species is thus the largest of the genus. On average, males are significantly larger than females and around twice as heavy. For example, on the Cedar Key Islands off the west coast of Florida, sexually mature females were on average 98.4 cm long, sexually mature males were on average 122.4 cm. Females weighed an average of 635 g, males 1,126 g.
Scaling
The species usually shows nine large, symmetrical shields on the top of the head. The parietals , however, are often fragmented into several smaller scales, particularly towards the end of the tail (posterior). In addition, the frontal often shows small scales adjacent to its corners. As the only representative of the genus, A. piscivorus has no rein shield ( Loreale ) between the nostril and the eye. The number of supralabials is 6 to 9, the number of infralabials 8 to 12.
The back scales are arranged in the middle of the body in 23-27, on average 25 longitudinal rows. The number of abdominal scales ( ventral shields ) varies in males between 130 and 145 in females between 128 and 144, the number of subcaudalia between 38 and 54 in males and 36 to 50 in females.
coloring
The basic color of the top is black, gray, yellow-brown, dark brown or dark olive-green. Depending on the population, there are on average 12 to 13 dark brown to black transverse bands on the back. These bands are often bordered by black and as light in the center as the basic color of the body. With increasing age, this banding becomes more and more indistinct, especially in the southeast of the area, old individuals can then be more or less monochrome dark. In general, representatives of the species in the eastern and southeastern part of the distribution area are paler in color and at the same time larger than those in the western two thirds of the area.
Young animals have a more noticeable appearance. They show clear, dark and light banding and a light yellow-green tail end. As they get older, the pattern fades and the light tail color changes from light green to the dark basic color of the rest of the body.
Similar species
Within its range, A. piscivorus can most likely be confused with the copper head ( Agkistrodon contortrix ). However, this lacks the postocular stripe (a wide stripe behind the eye), and the dorsal scales are in the middle of the body only in 21-25, on average 23, longitudinal rows. It is also much smaller and not tied to water. The other two species of the genus Agkistrodon are common in Mexico and Central America and do not occur in the USA.
distribution and habitat
The species lives in the water-rich lowlands in the southeastern United States. The distribution area largely corresponds to the natural area of the Atlantic coastal plain (Atlantic Coastal Plain). The range boundary of the species runs in the west through central Texas and the east of Oklahoma , in the north through the states of Missouri , Illinois and then, bypassing the Appalachians in the south , through Georgia , North and South Carolina and Virginia to the Atlantic coast. In the south the area ends on the border with Mexico , further east on the Gulf of Mexico or the Atlantic. The species regularly swims in salt water and has therefore colonized a number of islands off the coast in the southeastern United States.
Water moccasin otters are semi- aquatic and spend most of their life in or very close to permanent water; these can be slow-flowing rivers, lake shores, ponds, swamps and even brackish coastal deltas. In most of the distribution area, a close connection to forests is unmistakable; the species is characteristic of coastal pine forests (so-called flatwoods ) and bald cypress swamps. Due to the close ties to bodies of water, the occurrences are limited to areas below 500 m above sea level .
Subspecies
Today three subspecies are recognized. The distribution areas of the subspecies are directly adjacent to one another; there is a wide mixing zone in the edge areas.
- A. p. piscivorus : Along the east coast of the USA from Virginia to Alabama . The top and sides of the head are pale brown; banding of the upper side remains with age. The dark postocular stripe, a broad, horizontal stripe behind the eye, is weakly demarcated above and below by yellowish pigmentation; the snout shield ( rostral ) shows no dark stripes.
- A. p. conanti : Florida and southern part of Georgia . The top and sides of the head are very dark, almost black; in adult individuals the banding on the upper side is faint or faded. The postocular stripe is set off above and below by a very strong, light pigmentation. The snout shield ( rostrale ) and the adjacent nasal shields ( prae-nasalia ) and upper lip shields ( supralabialia ) show clear, vertical stripes.
- A. p. leucostoma : From the west of the state of Texas via eastern Oklahoma and Missouri to the north to the south of Illinois , to the east it reaches Kentucky , Tennessee and Alabama . The top and sides of the head are often very dark brown or black in both adults and young animals; the banding is often barely noticeable in adult individuals. The postocular stripe is hardly pronounced, particularly because of the very weak upper light border. The snout shield ( rostral ) also shows no dark stripes.
The closest relatives of the species are the Mexican moccasin viper ( A. bilineatus ) and Agkistrodon taylori .
behavior
These snakes are mostly nocturnal. In the morning or on cool days, they sunbathe on the banks of the water or on tree trunks, and also very much like on branches protruding above the water. On warm, sunny days the snake rests curled up, stretched out in the shade of the vegetation. The water moccasin otter swims with its head above the surface of the water. To hibernate, the snake looks for areas slightly higher up; Among other things, hollow trees and animal burrows have been identified as winter quarters.
nutrition
Like all pit vipers , the water moccasin otter has special pit organs between the nostril and eyes with which it perceives thermal radiation ( infrared light ) so that it can also hunt at night. However, the search for food also takes place visually and with the sense of smell. Small mammals and other terrestrial vertebrates are bitten at lightning speed and immediately released. If they don't succumb to the venom immediately, the snake will follow the scent until it finds the prey. Fish are held a little longer after being bitten than land vertebrates. Moccasins find it difficult to capture fish in open water; in an experimental study in the laboratory, only 13% of attacks on fish in open water were successful. Apparently, fish are mostly captured in drying water holes or in similar situations in which the freedom of movement of the fish is restricted.
The hunting behavior of young animals is unusual. These move their bright tails back and forth as bait to lure prey near them. With age, the color of the tail dwindles, as does its behavior.
The main prey of the water moccasin otters are fish and frogs in most of the area ; for example, in a study in Virginia, the three most common prey animals were the raspberry ( Rana clamitans ), sunfish ( Lepomis sp. ) and southern leopard frog ( Rana sphenocephala utricularia ). However, the food spectrum of the species is very broad and also includes practically all small vertebrates in their respective habitat, including small turtles , young alligators , lizards , snakes , birds and small mammals . Small vertebrates are also used as carrion , in one case even fish heads and entrails thrown into the water were eaten.
Young animals in particular also eat invertebrates , with cicadas , caterpillars and land snails , among others, being proven . At least in one study in Louisiana , the food spectrum showed clear gender-specific differences: males ate mainly fish, females mainly reptiles.
An extreme example of A. piscivorus' adaptability is the population on Seahorse Key , an anhydrous island belonging to the Cedar Key Islands in the Gulf of Mexico 12 km off the coast of Florida . From February to the end of August, water moccasin otters live there mainly on fish that fall from their nests in the heron and cormorant colonies there. During the rest of the year they mainly eat house rats ( Rattus rattus ) and various lizards.
Reproduction
Water moccasin otters are sexually mature at two years (males) or three years (females). They mate in autumn or in spring immediately after leaving their winter quarters. Similar to the closely related copper head , the females are apparently able to store sperm until spring after autumn mating.
Like all members of the genus, the species is viviparous ( ovoviviparous ); after three months of gestation, two to twelve, on average around eight, young are born between August and September. The young are 18 to 35 cm long at birth. Big females have more young; In a study in Florida, the smallest females (<80 cm body length) contained three to five embryos, the largest (> 100 cm body length) eight to eleven embryos.
It has been observed several times that females form small groups shortly before the young are born. After the birth, the young are guarded by the females for a few days.
Life expectancy
There is no information on the average and maximum age of wild individuals; in captivity, a water moccasin otter lived to be 24 years and 6 months old.
Population development and endangerment
Due to habitat changes, the species' population has declined in many parts of its range, but it is still common in suitable habitats. In a swampy area in Kentucky , the population was estimated at 300 individuals on 0.405 hectares (4,050 m²) in the 1950s; on the Mississippi , 50 individuals could be caught in one hour in the 1960s.
In very dry years the population apparently collapses regionally, but in normal humid years the population recovers very quickly. Overall, the species is still considered harmless.
Behavior towards people
Water moccasin otters are considered aggressive, but in a study aimed at shedding light on how wild water moccasin otters behave when they encounter humans, 51% of snakes attempted to flee and 78% used threatening gestures or other defensive tactics. Only 36% (13 out of 36) bit when they were reached with an artificial hand. In addition, many snakes did not inject poison when they were bitten. Such a "dry" bite could just be another threatening gesture. Unlike most snakes, the water moccasin otter stands up in danger and opens its mouth to warn attackers. This behavior is often interpreted as aggressive, but when left alone, she takes flight.
Laypeople in the USA often mistake every snake they encounter in or near bodies of water to be a water moccasin otter, which is usually a fallacy. Harmless water-dwelling snakes such as the swimming snakes ( Nerodia sp. ) Are much more common than the water moccasin otters, sometimes behave aggressively and imitate a pit viper by the posture of the head. This behavior is very convincing to laypeople. On land, the eastern hooked snake ( Heterodon platirhinos ) is often confused with the water moccasin otter . It also imitates the otter, if not as convincingly as the water snake, and hisses very loudly in defense.
Toxic effect on humans
The toxin mixtures of pit vipers are by far komplexesten natural poisons. They contain a mixture of enzymes , low molecular weight polypeptides , metal ions and other components whose function has so far hardly been understood. The effects of these poisons are correspondingly diverse.
The poison from A. piscivorus has a strong protein-degrading effect and therefore leads to tissue destruction . It causes severe pain, redness, swelling, and necrosis around the bite site. The poison has a hemolytic and anticoagulant effect ; in severe cases it can completely prevent blood clotting . It also causes the release of the peptide bradykinin , which among other things causes a drop in blood pressure, nausea, nausea, diarrhea and an increase in pain. It also contains the enzyme phospholipase A 2 , which has a toxic effect on muscle fibers.
There is no systematic record, but it is estimated that around 8,000 people are bitten by poisonous snakes each year in the USA. About 9% of the bites, or about 700, are caused by water moccasin otters. Deaths from A. piscivorus bites are very rare. The number of deaths from venomous snakes in the United States was estimated at nine to fourteen per year in the 1960s and 1970s. The majority of these deaths were due to bites from rattlesnakes ( Crotalus sp. ), Only 6.6% (less than one death per year) from water moccasin otters. For the 1980s and 1990s, the figures are expected to be considerably lower. This certainly also reflects the significantly improved medical treatment of snake bites.
The tissue destruction can, however, be irreversible and result in a permanent loss of function of the affected limb. Like other pit vipers, this species does not necessarily inject venom into the wound with every bite (see above), but every bite should be taken seriously and medical help sought, even if there is no immediate toxic effect.
Because of its toxicity, A. piscivorus is used in the snake- grabbing ritual practiced by a few American Pentecostal churches . In doing so, those involved accept a bite as proof of their faith.
Individual evidence
- ^ Charles A. Wharton: Reproduction and growth in the Cottonmouths, Agkistrodon piscivorus Lacépède, of Cedar Keys, Florida . Copeia 2, 1966: pp. 149-161
- ↑ Shawn E. Vincent, Anthony Herrel and Duncan J. Irschick: Comparisons of aquatic versus terrestrial strikes in the Pit classified, Agkistrodon piscivorus . Journal of Experimental Zoology 303A, 2005: pp. 476-488
- ↑ CL Cross: Natural History Notes: Agkistrodon piscivorus piscivorus (eastern cottonmouth). Diet . Herpetological Review 33 (1) 2002: pp. 55-56. quoted In: Jonathan A. Campbell and William W. Lamar: The Venomous Reptiles of the Northern Hemisphere . Comstock; Ithaca, London 2004: p. 692
- ^ Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere. Comstock; Ithaca, London 2004: p. 256
- ↑ Shawn E. Vincent, Anthony Herrel and Duncan J. Irschick: Ontogeny of intersexual headshape and prey selection in the pitphia Agkistrodon piscivorus . Biological Journal of the Linnean Society 81, 2004: pp. 151-159
- ^ Charles A. Wharton: Reproduction and growth in the Cottonmouths, Agkistrodon piscivorus Lacépède, of Cedar Keys, Florida . Copeia 2, 1966: pp. 149-161
- ^ Campbell & Lamar 2004
- ^ ER Allen and D. Swindell: Cottonmouth mocassin of Florida . Herpetologia 4 (Suppl. 1) 1948: pp. 1-16. Diagram based on data from the authors in: Jonathan A. Campbell and William W. Lamar: The Venomous Reptiles of the Northern Hemisphere . Comstock; Ithaca, London 2004: p. 259
- ^ AT Snider & JK Bowler: Longevity of reptiles and amphibians in North American collections. 2nd ed. Society for the Study of Amphibians and Reptiles, Herpetological Circular No. 21; 1992. Quoted in: Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere. Comstock; Ithaca, London 2004: p. 260
- ↑ Defensive Behavior of Cottonmouths (Agkistrodon piscivorus) toward Humans ( Memento from November 21, 2005 in the Internet Archive )
- ↑ For photos of the effects of bites see http://www.gifte.de/Gifttiere/agkistrodon_piscivorus_biss01.htm
- ^ Robert Norris: Venom Poisoning by North American Reptiles . In: Jonathan A. Campbell and William W. Lamar: The Venomous Reptiles of the Northern Hemisphere . Comstock; Ithaca, London 2004: p. 692
- ^ Robert Norris: Venom Poisoning by North American Reptiles . In: Jonathan A. Campbell and William W. Lamar: The Venomous Reptiles of the Northern Hemisphere . Comstock; Ithaca, London 2004: pp. 705-706
- ^ That Bites: Why do the snakes used in Pentecostal serpent handling have to be poisonous? , Slate , June 1, 2012
literature
- Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere . Comstock. Ithaca / London 2004, ISBN 0-8014-4141-2 .
Web links
- Information from the National Zoo, Washington, D. C. (Eng.)
- Agkistrodon piscivorus in The Reptile Database
- Agkistrodon piscivorus inthe IUCN Red List of Threatened Species 2013.1. Listed by: Hammerson, GA, 2007. Retrieved September 7, 2013.
