Echis


 * 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. The name Echis is a Greek word that means "viper." 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 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
*) 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.

Trivia

 * A saw scaled viper of the genus Echis may be responsible for biblical claims of a fiery flying serpent.