Russells viper

Appearance

The head is flattened, triangular, and distinct from the neck. The snout is blunt, rounded, and raised. The nostrils are large, each in the middle of a large, single nasal scale. The lower edge of the nasal scale touches the nasorostral scale. The supranasal scale has a strong crescent shape and separates the nasal from the nasorostral scale anteriorly. The rostral scale is as broad as it is high.

The crown of the head is covered with irregular, strongly fragmented scales. The supraocular scales are narrow, single, and separated by six to nine scales across the head. The eyes are large, flecked with yellow or gold, and surrounded by 10–15 circumorbital scales. The snake has 10–12 supralabials, the fourth and fifth of which are significantly larger. The eye is separated from the supralabials by three or four rows of suboculars. Of the two pairs of chin shields, the front pair is notably enlarged. The two maxillary bones support at least two and at the most five or six pairs of fangs at a time: the first are active and the rest replacements. The fangs attain a length of 16.5 mm in the average specimen.

The body is stout, the cross-section of which is rounded to circular. The dorsal scales are strongly keeled; only the lowest row is smooth. Mid-body, the dorsal scales number 27–33. The ventral scales number 153–180. The anal plate is not divided. The tail is short—about 14% of the total length—with the paired subcaudals numbering 41–68.

Dorsally, the color pattern consists of a deep yellow, tan, or brown ground color, with three series of dark brown spots that run the length of the body. Each of these spots has a black ring around it, the outer border of which is intensified with a rim of white or yellow. The dorsal spots, which usually number 23–30, may grow together, while the side spots may break apart. The head has a pair of distinct dark patches, one on each temple, together with a pinkish, salmon, or brownish V or X marking that forms an apex towards the snout. Behind the eye is a dark streak, outlined in white, pink, or buff. The venter is white, whitish, yellowish, or pinkish, often with an irregular scattering of dark spots.

Russell's viper grows to a maximum body and tail length of 166 cm and averages about 120 cm in mainland Asia. In islands, it is slightly shorter on average. It is more slender than most vipers. The following dimensions for a "fair-sized adult specimen" were reported in 1937:
⤷ Total length 1.24 m
⤷ Length of tail 430 mm
⤷ Girth 150 mm
⤷ Width of head 51 mm
⤷ Length of head 51 mm

Naming

The species is named after Patrick Russell, a Scottish herpetologist who first described many of India's snakes, and the name of the genus is from the Hindi word meaning "that lies hid", or "the lurker".

In English, common names of "D. russelii" include Russell's viper, chain viper, Indian Russell's viper, common Russell's viper, seven pacer, chain snake, and scissors snake.

Distribution

Russell's viper is found in India, Sri Lanka, Bangladesh, Nepal, and Pakistan. Populations from South-East Asia previously assigned to this species are now considered to be part of a different species, "Daboia siamensis". The type locality is listed as "India". More specifically, this would be the Coromandel Coast, by inference of Russell.

Within its range, it can be common in some areas, but scarce in others. In India, is abundant in Punjab, very common along the West Coast and its hills, in southern India especially in the state of Karnataka and north to Bengal. It is uncommon to rare in the Ganges valley, northern Bengal, and Assam.

Russell's viper is not restricted to any particular habitat, but does tend to avoid dense forests. The snake is mostly found in open, grassy or bushy areas, but may also be found in second growth forests, on forested plantations and farmland. It is most common in plains, coastal lowlands, and hills of suitable habitat. Generally, it is not found at altitude, but has been reported as far up as 2300–3000 m. Humid environments, such as marshes, swamps, and rain forests, are avoided.

This species is often found in highly urbanized areas and settlements in the countryside, the attraction being the rodents commensal with man.
As a result, those working outside in these areas are most at risk of being bitten. "D. russelii" does not associate as closely with human habitation as "Naja" and "Bungarus" species.

Behavior

Russell's viper is terrestrial and active primarily as a nocturnal forager. However, during cool weather, it alters its behavior and becomes more active during the day.
Adults are reported to be slow and sluggish unless pushed beyond a certain limit, after which they can become very aggressive. Juveniles, though, are generally more nervous.
When threatened, they form a series of S-loops, raise the first third of the body, and produce a hiss that is supposedly louder than that of any other snake. When striking from this position, they can exert so much force that even a large individual can lift most of its body off the ground in the process. These snakes are strong and may react violently to being picked up. The bite may be a snap, or they may hang on for many seconds.

Although this genus does not have the heat-sensitive pit organs common to the Crotalinae, it is one of a number of viperines that are apparently able to react to thermal cues, further supporting the notion that they, too, possess a heat-sensitive organ. The identity of this sensor is not certain, but the nerve endings in the supranasal sac of these snakes resemble those found in other heat-sensitive organs....hieroglyph snipped...

Habitat

Russell's viper is found in India, Sri Lanka, Bangladesh, Nepal, and Pakistan. Populations from South-East Asia previously assigned to this species are now considered to be part of a different species, "Daboia siamensis". The type locality is listed as "India". More specifically, this would be the Coromandel Coast, by inference of Russell.

Within its range, it can be common in some areas, but scarce in others. In India, is abundant in Punjab, very common along the West Coast and its hills, in southern India especially in the state of Karnataka and north to Bengal. It is uncommon to rare in the Ganges valley, northern Bengal, and Assam.

Russell's viper is not restricted to any particular habitat, but does tend to avoid dense forests. The snake is mostly found in open, grassy or bushy areas, but may also be found in second growth forests, on forested plantations and farmland. It is most common in plains, coastal lowlands, and hills of suitable habitat. Generally, it is not found at altitude, but has been reported as far up as 2300–3000 m. Humid environments, such as marshes, swamps, and rain forests, are avoided.

This species is often found in highly urbanized areas and settlements in the countryside, the attraction being the rodents commensal with man.
As a result, those working outside in these areas are most at risk of being bitten. "D. russelii" does not associate as closely with human habitation as "Naja" and "Bungarus" species.Russell's viper is terrestrial and active primarily as a nocturnal forager. However, during cool weather, it alters its behavior and becomes more active during the day.
Adults are reported to be slow and sluggish unless pushed beyond a certain limit, after which they can become very aggressive. Juveniles, though, are generally more nervous.
When threatened, they form a series of S-loops, raise the first third of the body, and produce a hiss that is supposedly louder than that of any other snake. When striking from this position, they can exert so much force that even a large individual can lift most of its body off the ground in the process. These snakes are strong and may react violently to being picked up. The bite may be a snap, or they may hang on for many seconds.

Although this genus does not have the heat-sensitive pit organs common to the Crotalinae, it is one of a number of viperines that are apparently able to react to thermal cues, further supporting the notion that they, too, possess a heat-sensitive organ. The identity of this sensor is not certain, but the nerve endings in the supranasal sac of these snakes resemble those found in other heat-sensitive organs....hieroglyph snipped...

Reproduction

Russell's viper is ovoviviparous. Mating generally occurs early in the year, although pregnant females may be found at any time. The gestation period is more than six months. Young are produced from May to November, but mostly in June and July. It is a prolific breeder. Litters of 20–40 are common, although fewer offspring may occur, as few as one. The reported maximum is 75 in a single litter. At birth, juveniles are 215–260 mm in total length. The minimum total length for a gravid female is about 100 cm. It seems that sexual maturity is achieved in 2–3 years. In one case, it took a specimen nearly 4.5 hours to give birth to 11 young.

Defense

Venom of this species is delivered by means of solenoglyphous dentition. The quantity of venom produced by individual specimens of "D. russelii" is considerable. Venom yields for adult specimens have been reported as 130–250 mg, 150–250 mg, and 21–268 mg. For 13 juveniles with an average total length of 79 cm, the venom yield ranged from 8 to 79 mg.

The LD50 in mice, which is used as a possible indicator of snake venom toxicity, is: 0.133 mg/kg intravenous, 0.40 mg/kg intraperitoneal, about 0.75 mg/kg subcutaneous. For most humans, a lethal dose is about 40–70 mg, well within the amount that can be delivered in one bite. In general, the toxicity depends on a combination of five different venom fractions, each of which is less toxic when tested separately. Venom toxicity and bite symptoms in humans vary within different populations and over time. In another study, Meier and Theakston reported that the lethality of venom of Russell viper varies with change in route of injection, as their results predicts the LD50 of 0.4 mg/kg through intraperitoneal route, 0.75 mg/kg/subcutaneous route and 0.3 mg/kg through intravenous route.