Mexican moccasin viper
| Mexican moccasin viper | ||||||||||||
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Mexican moccasin viper ( Agkistrodon b. Bilineatus ) |
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| Agkistrodon bilineatus | ||||||||||||
| Günther , 1863 |
The Mexican moccasin viper ( Agkistrodon bilineatus ) is a species of snake from the subfamily of pit vipers . It is also sometimes referred to as the Mexican moccasin . It occurs with three subspecies in coastal areas from northern Mexico to Costa Rica . The species mainly inhabits tropical deciduous and dry forests there. It feeds on a wide range of small vertebrates .
The Mexican moccasin otter is feared in large parts of its range due to its easy excitability, its aggressiveness and its toxicity and has caused a number of deaths, at least according to older reports. Today it is one of the most endangered species of snakes in America because of the ongoing destruction of its habitat.
description
The Mexican moccasin viper is a medium to large, powerful snake with a relatively long tail. The total length of adult animals is mostly over 80 cm, the previously known maximum length is 138 cm. Depending on the population, the tail accounts for an average of 19–23% of the total length in males and 16–22% in females.
Scaling
Like all species of the genus, the species usually shows 9 large, symmetrical shields on the top of the head. The parietals , however, are often fragmented into several smaller scales, especially towards the end of the tail (posterior), in some individuals the frontal is also fragmented or the praefrontals are separated by an elongated middle scale. The number of supralabials is 7 to 9, the number of infralabials 8 to 13.
The back scales are arranged in the middle of the body in 21-25, on the average in 23 longitudinal rows. The number of abdominal scales ( ventral shields ) varies in males between 127 and 142, in females between 128 and 144, the number of subcaudalia between 55 and 71 in males and 46 to 67 in females.
coloring
The basic color of the top is very variable depending on the individual, origin and age, from dark gray to almost black, dark gray-brown, dark yellow, reddish or red-brown. On the upper side of this basic color there are 10–19, depending on the population an average of 12–15 brown to blackish transverse bands, which are irregularly bounded by rows of diagonal, white, cream or yellow spots. The transverse bands are usually lighter than the basic color, but the colors become more and more similar with age. In general, large individuals are darker than smaller animals. The belly is gray, gray-brown or reddish-brown and irregularly lightly spotted.
The head is very striking. In almost all populations the head sides show two parallel, broad, light (mostly yellow) stripes. The upper lateral stripe of the head runs from the anterior tip of the rostral along the canthus to the rear over the edges of the internasalia , the prefrontalia and the supraocularia and then from the upper postocularia over the second horizontal row of the temporalia . It then bends downward and often merges with the rear end of the lower head side strip. The upper lateral stripe of the head is only missing in adults from southern Honduras , Nicaragua and Costa Rica . The lower lateral stripe of the head is significantly wider than the upper one and begins at the rostral or one of the praenasalia and then runs over the supralabialia backwards to the corner of the mouth. Then the lower side strip bends downwards and then continues backwards. In contrast to the very similar Agkistrodon taylori , this lower lateral stripe in the Mexican moccasin viper is darkly bordered down in front of the jaw edge in the front area, so it does not cover the entire lower outer edge of the supralabialia as in A. taylori . One or both head strips can be interrupted on the back of the head. Rostral and mental show a broad, vertical, light stripe.
The lower half of the iris is orange, rust brown or brown, the upper half is noticeably paler. The tongue is orange, red, or orange-pink with yellow tips.
In young animals, the distal half of the tail is light yellow or light yellow-green.
distribution and habitat
The area of the species mainly comprises coastal areas in Central America . On the Pacific coast, the distribution extends from southern Sonora in northern Mexico south to Costa Rica . The distribution area near the Atlantic is much smaller and limited to the Yucatan Peninsula and the north of Belize . Most of the evidence is available from heights below 600 m, the maximum was found in western Mexico at an altitude of 1500 m.
The descriptions of the habitat claims of the Mexican moccasin otters were partly contradicting; the species has been described as ground-dwelling by some authors and as semi-aquatic by others. The species predominantly inhabits seasonally dry forests, i.e. tropical dry forests, thorn bush forests and savannas . However, the species is quite adaptable, some populations permanently inhabit wet coastal marshes or the vicinity of ponds, others occur in areas with a pronounced and prolonged dry season, where the animals are in temporary small bodies of water and floodplains during the rainy season. Finally, the species has also been observed on rocky slopes that remain without water all year round.
Systematics
Today three subspecies are recognized. The distribution areas of the subspecies are directly adjacent to one another; there is a mixing zone in each of the edge areas.
- A. b. bilineatus ; the nominate form has the largest distribution area; it stretches along the Pacific from Mexico to El Salvador . The upper lateral strip of the head begins at the rostral and runs backwards over the canthus and the supraocularia and then obliquely over the second row of the temporalia. The lower light lateral stripe of the head begins at or near the internasal and runs over the anterior nasal to the rear over the supralabialia. The basic color of the trunk and the transverse ligaments are almost the same, the transverse ligaments usually have no lightening in the center. The belly is spotted throughout. The chin and throat are markedly bright.
- A. b. howardgloydi ; the distribution area includes the Pacific areas from Honduras to Costa Rica. The lower light lateral stripe of the head is divided in the front area, the two parts meet at an angle at the border between the second and third supralabials. This lower head side stripe is also accentuated by a narrow dark line on the upper edge. The lower areas of the supralabials are pale and undrawn and are the same color as the infralabials and the chin and throat. The upper lateral stripe of the head is narrow and often interrupted or absent behind the eye. The basic color of the chin and throat is orange or brownish orange and at the level of the first to sixth ventrals sharply set off from the other dark ventrals. The longitudinal middle third or quarter of the abdomen is faintly spotted or not at all. Young animals are red or reddish.
- A. b. russeolus ; the subspecies colonizes the Yucatan Peninsula and northern Belize . The upper lateral stripe of the head is narrow and often interrupted behind the eye. The lower lateral stripe of the head is wider than the upper one and is irregular to the rear from the corner of the mouth; there it often dissolves into individual spots or lines. The transverse banding of the trunk is usually noticeable even in adult animals.
The closest relative of the species is Agkistrodon taylori , which was only separated from the Mexican moccasin otter in 2000 as a separate species.
Activity and lifestyle
Like all species of the genus, the species is predominantly active at dusk and at night. As far as is known, the animals are only on the ground or in the water.
nutrition
As with the other species of the genus, the food spectrum is very broad and includes practically all small vertebrates of the respective habitat, i.e. amphibians , reptiles , birds and small mammals , young animals use their bright tail end as moving bait and presumably also eat invertebrates .
A study in Costa Rica found frogs and small lizards as food for young snakes, while adults ate mammals and the comparatively large black iguanas ( Ctenosaura sp.). A representative of the were detected as prey mouthed ( hypopachus variolosus ), a representative of Leptodactylidae ( Leptodactylus poecilochilus ) leading to the skinks belonging Mabuya unimarginata belonging to the teiidae belonging Ameiva undulata , the Common ctenosaura ( Ctenosaura similis ) belonging to the sting pocket mice belonging to Liomys salvini and a representative of the cotton rat ( Sigmodon hispidus ).
Reproduction
Like all species of the genus, Mexican moccasin otters give birth to their young alive, so they are viviparous . The number of young snakes per litter is 3 to 20, usually 5 to 10; the young animals have a total length of 25 to 32 cm. Four captive-born pups weighed 7.7–9.3 g. In Costa Rica, mating occurs from December to April and the young are born from June to August. Information on the average and maximum ages of individuals living in the wild is unknown; a maximum age of at least 24 years has been proven in captivity.
Poison and medicinal importance
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. bilineatus 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 , so that patients bleed from the bite site. It also contains the enzyme phospholipase A 2 , which has a toxic effect on muscle fibers. The tissue destruction can be irreversible and result in permanent loss of function of the affected limb.
The species is feared in its range because of its aggressiveness and has caused a number of deaths, some within a few hours of being bitten. Larger studies on the epidemiology are apparently not yet available, but overall the medical significance is apparently low compared to species of the American lanceolate and rattlesnake occurring in the same area of distribution .
Existence and endangerment
There are no reliable data on the size of the total population. In the last 50 years or so, however, the species has completely disappeared from at least parts of its range in Mexico and Guatemala , or has at least become very rare there. The main risk factors are habitat destruction through the conversion of their habitats into agricultural areas and extreme human persecution. The IUCN therefore classifies the Mexican moccasin otter as a type of the warning list (" near threatened" ), Campbell and Lamar count the species to the most endangered species of snakes in the Americas.
swell
Individual evidence
- ^ Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere. Comstock; Ithaca, London 2004, p. 251 and the literature cited there.
- ↑ Christopher L. Parkinson, Kelly R. Zamudio, Harry W. Greene: Phylogeography of the pitocket clade Agkistrodon: historical ecology, species status, and conservation of cantils. In: Molecular Evolution . 9 (4), 2000, pp. 411-420. doi : 10.1046 / j.1365-294x.2000.00854.x .
- ^ A. Solorzano, M. Romero, JM Gutierrez and M. Sasa: Venom composition and diet of the cantil, Agkistrodon bilineatus howardgloydi (Serpentes: Viperidae). Southwest. Nat. 44, pp. 478-483.
- ^ David A. Warrell: Snakebites in Central and South America: Epidemiology, Clinical Features, and Clinical Management . In: Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere. Comstock; Ithaca, London 2004, ISBN 0-8014-4141-2 , pp. 709-761.
- ^ Jonathan A. Campbell, William W. Lamar: The Venomous Reptiles of the Western Hemisphere. Comstock; Ithaca, London 2004, p. 252.
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
- Agkistrodon bilineatus in the endangered Red List species the IUCN 2008. Posted by: Cox, N., Chanson, JS & Stuart, SN (Global Reptile Assessment Coordinating Team), 2007. Retrieved on 1 November, 2008.
- Agkistrodon bilineatus in The Reptile Database
