African egg snakes
| African egg snakes | ||||||||||||
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Common egg snake ( Dasypeltis scabra ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Dasypeltis | ||||||||||||
| Wagler , 1830 |
The African egg snakes ( Dasypeltis ) are a genus of the family of the adder (Colubridae) in the subfamily of the land and tree snakes (Colubrinae).
description
Dasypeltis species are slender, rather graceful snakes with a small, blunt head that is only slightly separated from the body. They reach a length of 50 to 110 cm, whereby the females are slightly larger than the males. Your pupils are vertically elliptical in shape. Common to the species is the absence of the Loreal scale on the head. The half-divided nasal scale with the nostril is therefore directly adjacent to the pre-oculars . The middle chin shield is not divided by a mental pit. The 23 to 27 rows of body scales are heavily keeled. With three to four rows of scales on the sides of the body, these keels are also finely sawn. The coloration of the individual species, especially the common egg snake, varies greatly, which makes a correct determination difficult. The basic colors range from light brown to gray to dark olive. There are often black spots of varying density. Egg snakes are non-toxic. They only have between 3 and 7 small teeth per half of the jaw, which are hidden in the gums and cannot penetrate human skin, for example.
Distribution and habitats
The representatives of the genus are native to sub-Saharan Africa. Relic occurrences of the widespread species Dasypeltis scabra can also be found in the Atlas Mountains (SW Morocco ) and in the southwest of the Arabian Peninsula .
The preferred habitats range from savannahs to light forests and cultivated land. Deserts and closed, tropical forests are avoided.
Behavior and way of life
Daily rhythm
African egg snakes are crepuscular and nocturnal. During the day they like to hide in termite burrows. They are good climbers and swimmers.
nutrition
Together with the Indian egg snake ( Elachistodon westermanni ), the African egg snakes are the only purely oviphagenous (egg-eating) snakes in the world. Occasional oviphagia, however, occurs in several snakes. Depending on the subarea, the species and populations can specialize in different bird species. In the savannas, egg snakes regularly climb trees to get to the nests of weaver birds of the genus Ploceus . Once the snake has found a nest with fresh eggs, it first checks whether it can handle the size of the egg by feeling it with the underside of its head. Then she pushes her extremely flexible jaws over the egg and releases saliva on its surface. The very elastic skin in the front part of the body can be stretched three or four times, so that adult egg snakes that are about the size of a thumb can swallow eggs up to the size of a hen's egg. The egg is opened by pressing it along the vertebrae 17 to 38 protruding downward into the esophagus . The anterior of these enamel- coated appendages ( hypapophyses ) slit the egg. By contracting the muscles in this part of the body, the egg is then crushed on the widened middle pituitary gland and the liquid contents are swallowed. The emptied eggshell is compressed into a sausage-shaped spear ball. Forward-facing vertebral processes in another section prevent the eggshell from sliding into the stomach. Instead, it is brought back to the head and strangled by anti-peristaltic movements. Rotten eggs or eggs that have been incubated for a long time will not be eaten. In the north and south of their range, Dasypeltis species must be able to survive around six to eight months of fasting due to the birds' limited breeding season. During this time they feed on the body fat that they put on during the birds' breeding season.
Enemy behavior
Potential predators are mainly ophiophage (snake-eating) snakes such as liana snakes , cobras and boomslangs , but also baboons and wild boars . The Dasypeltis species are defenseless because of their weak dentition and the lack of poison glands . However, their appearance and behavior imitate poisonous snakes and are relatively well protected due to this mimicry . According to evolutionary researchers, the fact that very different venomous snakes occur in their large area of distribution is also the reason for the great color variability of egg snakes. The populations occurring in different regions of Africa imitate echis species (e.g. Echis pyramidum ), puff adders (e.g. Bitis caudalis ), bush vipers , swamp vipers ( Proatheris superciliaris ) or toad vipers such as Causus rhombeatus, depending on the sympatric models . In addition, the animals can straighten up, inflate their front bodies slightly and push at the enemy. Another form of defense behavior is that they lay their bodies in parallel U-shaped loops and constantly move them so that the ribbed scale keels on the sides of the body rub against each other and create a characteristic sound similar to that of poisonous sand rattle otters .
Systematics and research history
The genus Dasypeltis was established by Johann Georg Wagler in 1830 , after the animals had previously mostly been classified in the genus Coluber . In 1834, the French naturalist Claude Jourdan first observed and described nutrition and pointed out its anatomical features. A detailed study of this behavior and the adaptations on which it is based was presented in 1952 by the German engineer and zoologist Carl Gans . The same author also published a revision of the genre in 1959.
According to the Reptile Database , 16 species are distinguished:
- Dasypeltis abyssina
- Dasypeltis arabica
- Dasypeltis atra
- Dasypeltis bazi
- Dasypeltis confusa
- Dasypeltis crucifera
- Dasypeltis fasciata
- Dasypeltis gansi
- Dasypeltis inornata
- Dasypeltis latericia
- Dasypeltis medici
- Dasypeltis palmarum
- Dasypeltis parascabra
- Dasypeltis sahelensis
- Dasypeltis scabra
- Dasypeltis taylori
swell
- George A. Boulenger: Catalog of the Snakes in the British Museum (Natural History) , Volume 2, Reprint 1961.
- William R. Branch: Field Guide to Snakes and other Reptiles of Southern Africa , 2nd ed., 1998.
- Maurice Burton & Robert Burton: International Wildlife Encyclopedia , 3rd ed., 2002.
- Harry U. Greene, Patricia Fogden, Michael Fogden: Snakes: The Evolution of Mystery in Nature , 2000.
- Hans-Hermann Schleich, Werner Kästle, Klaus Kabisch: Amphibians and Reptiles of North Africa. Biology, Systematics, Field Guide , 1996.
- Dasypeltis in The Reptile Database
- Map of the distribution areas of D. scabra , D. salehensis , D. confusa , D. abyssina and D. atra
Individual evidence
further reading
- Carl Gans: The Functional Morphology of the Egg-Eating Adaptations in the Snake Genus Dasypeltis. Zoologica 37 (1952): 209-244.
- Carl Gans: A taxonomic revision of the African snake genus "Dasypeltis" (Reptilia: Serpentes) . Annales du Musée Royal du Congo Belge 74 (1959).
