Western sand boa
| Western sand boa | ||||||||||||
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Western sand boa from Pylos (Peloponnese / Greece) |
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| Eryx jaculus | ||||||||||||
| ( Linnaeus , 1758) |
The western sand boa ( Eryx jaculus ) is a species from the boas family (Boidae) with a body length of up to about 80 centimeters. It is the only giant snake that is native to a larger area of Europe ; the eastern sand boa ( Eryx miliaris ) can only be found on the northwestern shore of the Caspian Sea .
features
The western sand boa has a yellow to light brown basic color, with brown to black irregular spots and bands. The females are about 46-71 cm long, the males 30-46 cm, the maximum length measured in an individual was 83.8 cm. Members of island populations , for example from the Mediterranean island of Corfu , usually remain significantly smaller with maximum lengths of around 60 cm. The tail is rather short, about seven to ten percent of the body length. The physique is compact and the head is not detached from the body.
What is striking about the shape of the head is the protruding grave formed from the arched and elongated parietal shield on the otherwise rounded head tip. A parietal ridge is poorly developed and hardly recognizable. In contrast to the eastern sand boa, in which the eyes are located on the top of the head, in the western sand boa these have a large distance from each other and are located on the sides of the head. The head narrows sharply towards the mouth, so that the edges of the mouth are clearly sunk and the subocularia lying under the eyes are not visible from above.
The rostral is broadly trapezoidal and extends far beyond the mental area of the lower jaw. The snake also has two internasalia (shields between the nostrils) and two to three post-internasalia directly behind them. Between these and the interorbital region (area between the eyes) there are two to seven head shields and in the direct line between the eyes there are two to five head shields. Six to twelve circumocularia are arranged around the eyes and between the preocularia and postnasalia there are two to three lorealia . The mouth gap is delimited at the upper edge by seven to eleven supralabials .
At its thickest point, the body has 41 to 57 longitudinal rows of dorsal scales. The scales are as smooth as possible, a weak keel occurs in the last third of the trunk and on the upper side of the tail. The throat has very small, elongated scales that merge on the neck into the 161 to 200 abdominal scales ( ventralia ) formed as a wide row . 15 to 36 subcaudalia adjoin the large and undivided anal shield . To the side of the anal shield, the rudimentary remains of the rear extremities are clearly visible as dew spurs , which are larger in the males than in the females.
distribution and habitat
The distribution area of the western sand boa extends from Iran and Iraq over the Middle East and North Africa to the Balkans and Southeast Europe and in the Transcaucasus to the Caspian Sea . This is where the distribution area of the Eastern Sand Boa ( Eryx miliaris ) joins, which extends to Central Asia.
The species prefers dry areas with loose layers of sand as a habitat. Vacant rodent structures are taken over, with their own corridors being built.
Way of life
activity
The activity of the western sand boa is mainly dependent on the respective daytime temperature and thus varies from region to region. Wintering takes place mainly in the high mountain regions of the Caucasus , where the snakes retreat to underground wintering quarters between November and March, some of which are several meters deep in the ground. In contrast, in Southeastern Europe, Asia Minor and North Africa there are only very short or no wintering phases, as the daytime temperatures in Libya and Egypt are still between 10 and 20 ° C in January. Short-term wintering occurs in the low mountain regions of Tunisia and northern Algeria .
The daily activity is also temperature dependent. In times of the year when the mean daily temperature is below 20 ° C, the western sand boa is almost exclusively diurnal, at higher temperatures it shifts its activity to cooler mornings or dusk. At temperatures above 30 ° C, the snake is rarely found outdoors and usually hides in its shelter under stones or in earthen structures.
nutrition
The food of the snake includes mainly small mammals, lizards and large insects, depending on its body size and the range of food in its habitat ; ground-nesting birds and larger nudibranchs can also be preyed on. The snake lies in wait for its prey in its hiding place or leaves it, especially at night, to actively hunt.
As with most giant snakes, the prey is grabbed with the mouth and then quickly embraced by the body until it is suffocated. Then they are swallowed whole.
Reproduction and development
A female mates with several males in different regions from the end of March to July. After a gestation period of about four months, the mother gives birth to live young ( ovoviviparia ), which are surrounded by transparent egg shells, which are then pierced.
Predators
Little is known about potential predators of the western sand boa. There are obviously no predators that specialize in capturing this species, on the other hand it can be assumed that young animals and small individuals in particular are regularly captured by predators such as foxes, dogs and cats or by birds of prey and owls . In barn owls in Israel , skeletal remains of the western sand boa have been found in crusts , although not often. Sand boas are also likely to be potential prey for larger snakes.
Systematics
Research history and fossil record
The western sand boa was first scientifically described by Carl von Linné in 1758 as Anguis jaculus . The terra typica was Egypt , the type specimen used for this description is no longer available today. In 1801, the French naturalist Guillaume-Antoine Olivier classified the species in the genus Boa as B. turcica based on his own collection copies . In 1831, the classification was done in the 1803 by François-Marie Daudin described and which still exists genus Eryx by Karl Eichwald as Eryx familiaris.
The western sand boa or very closely related species has been known to be fossilized since the Miocene . Fossils, which can probably be assigned to this species, were also found in Spain and thus outside of today's distribution area. On the basis of these finds and the finding of a species known as Eryx primitivus, which also came from Spain, it is concluded that the range of the species in the Miocene included the entire Mediterranean region.
External system
The western sand boa is classified as a species in the genus of the real sand boas ( Eryx ). Within the genus, skeletal and scale features are mainly used to differentiate between species and for systematic investigations. The western sand boa is therefore very likely to be the sister species of the Indian sand boa ( Eryx johnii ). Both together represent the most widely derived forms within the genus, the closest related species are the large sand boa ( Eryx tataricus ) and the eastern sand boa ( Eryx miliaris ).
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Subspecies
Depending on the source, different numbers of subspecies of the western sand boa are described, which differ mainly due to the shape and number of scales ( pholidosis ). After a comprehensive review of all the subspecies described, Tokar and Obst came to the conclusion in 1993 that only two subspecies should be recognized:
- E. j. jaculus as a nominate form in North Africa with an Arab distribution area up to the Suez Canal
- E. j. turcicus as a subspecies in Southeastern Europe, Asia Minor, the Caucasus as well as Iran and Iraq.
Above all, the E. j. familiaris and E. j. urmianus the E. j. turcicus and combined into a single subspecies. E. j. turcicus represents a very diverse form in terms of its features, which can show regional differences.
Threat and protection
The species is listed in the Washington Convention on the Protection of Species in Appendix 2 and Appendix A of the EU Species Protection Ordinance . This means that the animals may not be taken from nature, owners of these animals must be able to show a certificate of origin ( CITES ). They are also in the Fauna-Flora-Habitat Directive of the European Union included in Annex 4, and since 1998 by the Federal Nature Conservation Act classified protected as special.
These animals are rarely kept in private terrariums and are therefore rarely bred .
supporting documents
Individual evidence
Most of the information in this article has been taken from the sources given under literature; the following sources are also cited:
- ↑ Ilya S. Darewskij: Eryx miliariis (Pallas, 1773) - Eastern sand boa in Wolfgang Böhme: (Ed.) Handbook of reptiles and amphibians in Europe; Volume 3 / I, Schlangen (Serpentes) I Aula-Verlag, Wiebelsheim 1993; Pages 35-53. ISBN 3-89104-003-2
- ^ Yoram Yom-Tov, David Wool: Do the Contents of Barn Owl Pellets Accurately Represent the Proportion of Prey Species in the Field? In: The Condor. 99, 4, 1997, pp. 972-976.
- ↑ Zbigniew Szyndlar, Hans-Hermann Schleich: Two species of the genus Eryx (Serpentes; Boidae; Erycinae) from the Spanish Neogene with comments on the past distribution of the genus in Europe. In: Amphibia-Reptilia. 15, 3, 1994, pp. 233-248
- ^ Arnold G. Kluge: Calabaria and the phylogeny of erycine snakes. In: Zoological Journal of the Linnean Society. 107, 4, 1993, pages 293–351 (full text as PDF; 2.5 MB)
- ↑ Tokar and Obst 1993, pp. 46-49
- ↑ Listing according to CITES, EU, FFH and BNatSchG
literature
- Anatoli A. Tokar, Fritz Jürgen Obst : Eryx jaculus (Linnaeus, 1758) - Western sand boa. In: Wolfgang Böhme (Ed.): Schlangen (Serpentes) 1. Aula, Wiebelsheim 1993, ISBN 3-89104-003-2 (Handbook of Reptiles and Amphibians in Europe, Volume 3/1), pages 35-53.
- Ulrich Gruber: The snakes of Europe. Franckh, Stuttgart 1989, ISBN 3-440-05753-4 , pages 61-62.
- Zdenek Vogel: Giant snakes from all over the world. Westarp-Wissenschaften, Magdeburg 1973, ISBN 3-89432-463-5 (Neue Brehm-Bücherei, Volume 402).
