Snakes of Pakistan: Russell's Viper

Description and Biology:
This is a large snake with an average length of 0.7 to 1.3 meters and a maximum length of 1.7 meters. The head is rather long, triangular, slightly distinct from neck, with large, conspicuous nostrils on side of snout. The Fangs are large and the tail short. The ground color may be dark brown, brownish-yellow,, or brownish-gray. Immature specimens are usually clear orange to brownish-orange. Dorsal pattern consists of black or brown oval spots edged with black, white, or both. Spots in middle row may fuse together to form zig-zag pattern. Two rows of oval spots run along each side of body. The tail is striped. Belly pinkish-brown or whitish with black spots; becoming darker towards tail. Three separate semi triangular spots on top of head are situated to form triangle with vertex between eyes. A dark band runs diagonally from eye to corner of mouth.

General characteristics:
Head longer than broad, distinct from neck, body stout, dorsoventrally flattened; nostril large in a crescent-shaped, large nasal scale; the supraocular scale not divided; 11-12 supralabials separated from eye by 3-4 rows of small scales; 13-15 infralabials; anterior genial short, wide, posterior not differentiated; dorsals strongly keeled in 27-33 rows at midbody; ventrals 164-178, subcaudals 46-58, anal entire.

Dorsum light yellowish brown to sandy, with a median series of 22 to 32, large, oval, chestnut blotches, bordered with black or dark brown, narrowly edged with cream, arranged longitudinally, mostly fused with each other to form a mid dorsal chain. A lateral series of similar but smaller spots, which on lower side are with scattered dark flecks with lighter edges. A pair of dark spots at the base of head. A light V-shaped canthal mark with apex on the snout. Labials mottled with brown and cream, ventrum pinkish white with curved dark spots. Throat white.

Russell's Viper (Daboia ruselii), defensive posture
Photo Credit: Dr. Muhammad Sharif Khan

Biology:
This snake is primarily nocturnal (especially during hot weather). Lethargic during day, but can be quiet active at night. Usually keeps to the shade of bushes and grass growing along paths, where due to its characteristic body color and pattern, it is difficult to be located. It shelters in rodents burrows, old termite mounds, rock crevices, piles of leaves, or other debris. Also found near human dwellings searching for prey. May be active during day in cool weather. Can be very excitable. Coils and will hiss when disturbed. When excited, body will vibrate and emit a low rasping sound resulting from scales of one part of coiled body rubbing upon another. It generally strikes only at objects within its effective striking range, but may strike quickly without provocation. The venom of this snake can deliver 2 to 3 times the lethal venom dose and causes most of the snakebite fatalities in the areas where it occurs.

Breeding season extends from April to July, gravid females are collected up to September, viviparous, 20-25 young are born.

Diet includes small mammals such as rats, mice and birds. Prey is stalked and bitten and released, when helpless it is taken.

Habitat, Distribution and Status:
The chain viper inhabits mesic habitat of grass fields, saltish scrubby areas, along marginal growths of water bodies, hedges and fences, gardens and gally forests. Occurs in plains, savannahs, foothills montane areas (moist, cool upland slopes below timberline) at elevations upto 2,200 meters.

The Russell's viper is found in Pakistan from India-Pakistan border to Indus Valley in provinces of Sind and Punjab. It extends from Karachi to Rawalpindi, at low altitudes. It is reported from throughout India to Bangladesh, extending into peninsular India and Sri Lanka. It has been distinguished into several races which are widely distributed throughout southeast Asia up to Taiwan.

Daboia ruselii ()

Map Credit: Dr. Muhammad Sharif Khan