By Kay Van Damme, Ghent University, Belgium, for SGBP
Reptiles are “cold-blooded” scaled vertebrates that breathe air through lungs. Most species rely on external heat sources to maintain their body temperature, which makes them well-known sunbathers. The group includes turtles, snakes, lizards, chamaeleons and many others, most of which are classified under the order Squamata (from “squama”, scale).
Endemism and threats
The Socotra Archipelago currently counts about 30 species of terrestrial reptiles of which cca. 90 % is endemic, many of which with restricted distributions even on the Archipelago (Rössler & Wranik, 2004). The group has been studied since the end of the 19th century, yet new species are still being described even in 2009. Molecular studies show that the Socotran endemic reptiles take in a special, relatively ancient position.
The largest diversity of reptiles on Socotra is made up by the geckoes, of which both day- and night-active species occur, feeding on invertebrates (ants, termites, grasshoppers, etc.). The day-active geckoes can be frequently seen on rocks, houses or stones, scurrying away and sometimes, signaling with their tails. Four marine turtles are also known from Socotran beaches.
Reptiles frequently form the basis of myths and legends. An ancient written report exists of giant reptiles on the island. The crocodiles, giant lizards and several species of tortoises (of which one giant species) that were mentioned, are not present on Socotra now and their existence is not confirmed. Locally, vivid legends exist about mysterious, giant snakes on the island, some of which strong enough to kill a goat.
Abundant on Socotra, reptiles form a key group in the ecosystem, both as predators of smaller invertebrates, as food item for birds (of prey) and likely as pollinator of several fruiting plants, as on many other islands.
UNFORTUNATELY, this group is under threat on Socotra. As most are endemic species, that have adapted since long to the local environment before the arrival of man, disturbances are likely to be felt strongly. For example, introduced mammals such as rats and civet cats, actively prey on reptiles and put pressure on local reptile populations. Secondly, changes on land, such as road building or clearing, are habitat destructions with negative effect on reptile populations. Overgrazing, which is becoming a major problem on Socotra, is also known to have an impact on reptile diversity and even behaviour. Finally, overcollecting may be a real threat and the collection of these animals is NOT allowed.
Examples of Socotran Reptiles
Chamaeleonidae (Chamaeleons) (1)
Chamaeleo monachus Gray, 1864– Monarch Chamaeleon. Endemic to Socotra; the one and only Socotran chamaeleon. Like other chamaeleons, this animal may change color, from grey to brown to green, depending on its place and mood. It makes a hissing sound when alarmed. Molecular studies suggest that the Socotra species may be a true relict within the genus.
Scincidae (Skinks) (2)
Trachylepis socotrana Peters, 1882 – Socotra Skink. Endemic skink, commonly seen on house walls or between cracks by daytime. Also as Mabuya socotrana (Peters, 1882), pending taxonomical decisions. Skinks look similar to lizards but have shorter legs (some have even lost their legs).
Typhlopidae/Leptotyphlopidae (Blind Snakes and Slender Blind Snakes) (4)
Typhlops socotranus Boulenger, 1893 – Socotra Worm Snake. Endemic blind snake, wormlike and small, lives under stones and in soil. One of four burying snakes on the island, which escape the eye of most. Another genus of small blind snakes here is Leptotyphlops.
Trogonophidae (Shorthead Worm Lizards) (1)
Pachycalamus brevis Günther, 1881. Short Worm Lizard. Endemic. Worm lizard, part of an ancient group of legless lizards, wormlike in appearance and unique to Socotra.
Colubridae (Racers) (2)
Hemerophis socotrae (Günther, 1881) – Socotran Racer. Endemic and a monotypic genus (means there is only one species in this genus). Dark or orange/yellow with black banded, relatively common. The family of colubrids is also called “Racers”, as these snakes can move relatively fast. They form a group of snakes with round pupils.
Ditypophis vivax Günther, 1881 – Günther’s Racer. Endemic and also monotypic, viper-like in appearance. Together with the former, one of only two well-known “true” snakes on the islands.
Lacertidae (Wall Lizards) (2)
Mesalina balfouri Blanford, 1881 – Socotra Sand Lizard. Endemic lizard, very common on stones basking in the sun. Named after the botanist I.B. Balfour, a botanist from the RBGE that studied the Socotran flora in the end of the 19th century.
Gekkonidae (Geckos) (19)
Haemodracon riebeckii (Peters, 1882) – Socotra Giant Gecko. Endemic genus and species. Largest nocturnal gecko on the island, frequently found associated with Dracaena trees or foun in rock holes. Named after E. Riebeck, a German naturalist.
Hemidactylus forbesii Boulenger, 1899 – Socotra Leaf-toed Gecko. Endemic to Abd al Kuri. Nocturnal gecko, named after H.O. Forbes, who contributed a great deal to the Socotran fauna.
Pristurus sokotranus Parker, 1938 – Socotra Rock Gecko. Endemic. Day-active gecko, commonly found on stones. The genus Pristurus contains “semaphore” geckoes, which may signal by moving their tail up and down (“flagging”).
Rösler, H. & Wranik, W. (2004). A key an annotated checklist to the reptiles of the Socotra Archipelago. Fauna of Arabia, 20, 505-534.
The Socotran Dragonís Blood tree faces a realistic risk of extinction on the island.