Echis

Echis
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Reptilia Order: Squamata Suborder: Serpentes Family: Viperidae Subfamily: Viperinae Genus: Echis Merrem, 1820
Synonyms
Echis - Merrem, 1820 Toxicoa - Gray, 1849 Turanechis - Cherlin, 1990

Common names: saw-scaled vipers, carpet vipers.

Echis is a genus of venomous vipers found in the dry regions of Africa, the Middle East, India and Sri Lanka. These snakes are quick-tempered and strike readily, which, combined with a virulent hemotoxic venom, makes them very dangerous, despite their small size. They also have a characteristic threat display, rubbing sections of their body together to produce a "sizzling" warning sound. Eight species are currently recognized.

Description

Relatively small in size with adults never larger than about 90 cm in length (E. pyramidum).

The head is short, wide, pear-shaped and distinct from the neck. The snout is short and rounded, while the eyes are relatively large and set well forward. The crown is covered with small, irregular, imbricate scales, which may be either smooth or keeled.

The body is moderately slender and cylindrical. The dorsal scales are mostly keeled. However, the scales on the lower flanks stick out at a distinct 45-degree angle and have a central ridge, or keel, that is serrated (hence the common name). The tail is short and the subcaudals single.

Geographic range

India and Sri Lanka, parts of the Middle East and Africa north of the equator.

Behavior

All members of this genus have a distinctive threat display, which involves forming a series of parallel C-shaped coils and rubbing them together to produce a sizzling sound, rather like water on a hot plate. The proper proper term for this is "stridulation." As they become more agitated, this stridulating behavior becomes faster and louder. It is postulated that this display evolved as a means of limiting water loss, such as might occur when hissing. However, some authors describe this display as being accompanied by loud hissing.

These snakes are very aggressive and will strike vigorously from the position described above. When doing so, they may overbalance and end up moving towards their aggressor as a result; most unusual behavior for a snake.

Feeding

Little is known about the eating habits of some species, but of others the diet is reported to be extremely varied, and may include items such as locusts, beetles, worms, slugs, spiders, scorpions, centipedes, solifugids, frogs, toads, reptiles (including other snakes), small mammals and birds.

Reproduction

Most Echis species, such as those found in Africa, are oviparous, while others, such as those in India, are viviparous.

Venom

Bites from Echis species probably result in more deaths than from any other species. The genus is recognized as medically significant in many tropical rural areas. They may be small, but they are very aggressive, quick to strike and possess an extremely virulent hemotoxic venom. There seems to be no significant correlation between the length of the specimen and the symptomology signs that occur in humans. Most victims are bitten after dark when these snakes are active.

Most of these species have venom that contains factors that can cause a consumption coagulopathy and defibrination which may persist for days to weeks. This may result in bleeding anywhere in the body, including the possibility of an intracranial hemorrhage. The latter classically occurs a few days following the bite.

Venom toxicity varies among the different species, geographic locations, individual specimens, sexes, over the seasons, different milkings, and of course the method of injection (SC, IM, IP, IV). Consequently, the LD₅₀ values for Echis venom differ significantly. In mice the intravenous LD₅₀ ranges from 2.3 mg/kg (U.S. Navy, 1991), to 24.1 mg/kg (Christensen, 1955) to 0.44-0.48 mg/kg (Cloudsley-Thompson, 1988). In humans, the lethal dose is estimated to be 3-5 mg (Minton, 1967). Latifi (1991) notes that venom from females was more than twice as toxic on average than venom from males.

The amount of venom produced also varies. Reported yields include 20-35 mg of dried venom from specimens 41-56 cm in length (Minton 1974, U.S. Navy, 1991), 6-48 mg (16 mg average) from Iranian specimens (Latifi, 1991) and 13-35 mg of dried venom from animals from various other localities (Boquet, 1967). Yield varies seasonally, as well as between the sexes: the most venom is produced during the summer months and males produce more than females.

Species

Species	Authority	Subsp.*	Common name	Geographic range
E. carinatusT	(Schneider, 1801)	4	Saw-scaled viper	Southeastern Arabian Peninsula (Oman, Masirah and eastern UAE), southwestern Iran, Afghanistan, Uzbekistan, Turkmenistan, Tadzikhistan, Pakistan (including Urak near Quetta and Astola Island off the Makran Coast), India, Sri Lanka and Bangladesh.
E. coloratus	Günther, 1878	0	Palestine saw-scaled viper	Southeastern Egypt east of the Nile and as far south as the 24th parallel, Sinai, Israel, Jordan, and the Arabian Peninsula in Saudia Arabia, Yemen and Oman.
E. hughesi	Cherlin, 1990	0	Hughes' saw-scaled viper	Somalia: northern Migiurtinia, near Meledin.
E. jogeri	Cherlin, 1990	0	Joger's saw-scaled viper	Western and central Mali.
E. leucogaster	Roman, 1972	0	White-bellied carpet viper	West and north-west Africa: extreme southern Morocco, Western Sahara, Algeria ((Ahaggar), the southern region of Mauritania, Senegal, northern Guinea, central Mali, Burkina Faso, western Niger and northern Nigeria.
E. megalocephalus	Cherlin, 1990	0	Cherlin's saw-scaled viper	Red Sea island between Yemen and Eritrea (Dahlak Archipelago).
E. ocellatus	Stemmler, 1970	0	African saw-scaled viper	Northwest Africa: Mauritania, Senegal, Mali, Guinea, Ivory Coast, Burkina Faso, Ghana, Togo, Benin, southern Niger, Nigeria, northern Cameroon and southern Chad.
E. pyramidum	(Geoffroy Saint-Hilaire, 1827)	2	Egyptian saw-scaled viper	In northeastern Africa: northern Egypt and central Sudan, Eritrea, Ethiopia, Somalia and northern Kenya. In the southwestern Arabian Peninsula: scattered populations in western Saudi Arabia (south of the 18th parallel), Yemen, South Yemen (Hadhramaut) and Oman (Dhofar). Disjunct populations apparently also occur in the northern regions of Libya, Tunisia and Algeria.

*) Not including the nominate subspecies (typical form).
^T) Type species.

Taxonomy

Some sources also mention several other species:

• E. omanensis, Babocsay 2004. A new species found in the United Arab Emirates and east Oman.
• E. khosatzkii, Cherlin 1990. Found in Oman and Yemen. Considered a synonym of E. pyramidum.
• E. multisquamatus, Cherlin 1981. Described here as E. carinatus multisquamatus.

See also

• Viperinae.
• List of viperine species and subspecies.
• True vipers - Common names.
• True vipers - Synonymy.
• Snakebite.

Other references

• Boquet P. 1967. Pharmacology and toxicology of snake venoms of Europe and the Mediterranean regions. In: Bucherl W, editor. 1967. Venomous Animals and their Venoms. Vol. I. Paris: Masson. pp 340-58.
• Boulenger GA. 1890. The Fauna of British India, Including Ceylon and Burma. Reptilia and Batrachia. Taylor & Francis, London, xviii, 541 pp.
• Christensen PA. 1955. South African Snake Venoms and Antivenins. Johannesburg: South African Institute of Medical Research. 35 pp.
• Cloudsley-Thompson JL. 1988. The saw-scaled viper Echis carinatus. British Herpetological Society Bulletin 24:32-3.
• Latifi M. 1991. The snakes of Iran. Published by the Department of the Environment and the Society for the Study of Amphibians and Reptiles, 2nd edition. 156 pp.
• Minton SA Jr. 1967. Snakebite. In: Beeson PB, McDermott W, editors. Cecil and Loeb Textbook of Medicine. Philadelphia: Saunders. 420 pp.
• Minton SA Jr. 1974. Venom Diseases. Springfield (IL): CC Thomas Publ. 386 pp.
• U.S. Navy. 1991. Poisonous Snakes of the World. US Govt. New York: Dover Publications Inc. 203 pp. ISBN 0-486-26629-X.

External links

• Echis at Herpbreeder.com. Accessed 9 September 2006.
• Echis photo gallery at Herpetology of Africa. Accessed 9 September 2006.