Daboia

Common names: Russell's viper,^[2][3] chain viper,^[4][5] Indian Russell's viper,^[6][7] (more).

Daboia is a monotypic genus^[8] created for a venomous viper species, D. russelii, which is found in Asia throughout the Indian subcontinent, much of Southeast Asia, southern China and Taiwan.^[1] Due largely to its irritable nature, it is responsible for more human fatalities than any other venomous snake.^[9] Within much of its range, this species is easily the most dangerous viperid snake and a major cause of snakebite injury and mortality.^[2] It is a member of the big four venomous snakes in India, which are together responsible for nearly all Indian snakebite fatalities.^[10] The species was named in honor of Dr. Patrick Russell (1726–1805), who had earlier described this animal, and the genus after the Hindi name for it, which means "that lies hid", or "the lurker."^[11] Two subspecies are currently recognized, including the nominate subspecies described here.^[12]

Contents 1 Description 2 Common names 3 Geographic range 4 Habitat 5 Behavior 6 Feeding 7 Reproduction 8 Captivity 9 Venom 10 Subspecies 11 Taxonomy 12 Mimicry 13 See also 14 References 15 Further reading 16 External links

Description

This snake grows to a maximum length of 166 cm (5.5 ft). The average length is about 120 cm (4 ft) on the mainland, although island populations do not attain this size.^[2] It is more slenderly built than most other vipers.^[13] Ditmars (1937) reported the following dimensions for a "fair sized adult specimen":^[14]

Total length	4 ft., 1 inch	124 cm
Length of tail	7 inches	18 cm
Girth	6 inches	15 cm
Width of head	2 inches	5 cm
Length of head	2 inches	5 cm

The head is flattened, triangular and distinct from the neck. The snout is blunt, rounded and raised. The nostrils are large, in the middle of a large, single nasal scale. The lower edge of the nasal touches the nasorostral. The supranasal has a strong crescent shape and separates the nasal from the nasorostral anteriorly. The rostral is as broad as it is high.^[2]

The crown of the head is covered with irregular, strongly fragmented scales. The supraocular scales are narrow, single, and separated by 6–9 scales across the head. The eyes are large, flecked with yellow or gold, and each is surrounded by 10–15 circumorbital scales. There are 10–12 supralabials, the 4th and 5th of which are significantly larger. The eye is separated from the supralabials by 3–4 rows of suboculars. There are two pairs of chin shields, the front pair of which are 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.^[2] The fangs attain a length of 16 mm in the average specimen.^[15]

The body is stout, the cross-section of which is rounded to cylindrical. The dorsal scales are strongly keeled; only the lower 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 body length — with the paired subcaudals numbering 41–68.^[2]

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 its 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 pattern that forms an apex towards the snout. Behind the eye, there 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.^[2]

Common names

• English – Russell's viper,^[2] chain viper,^[4][5] Indian Russell's viper,^[6][7] common Russell's viper,^[16] seven pacer,^[17] chain snake, scissors snake.^[18] Previously, another common name was used to described a subspecies that is now part of the synonymy of this form: Sri Lankan Russell's viper for D. r. pulchella.^[16]
• Urdu, Hindi, Hindustani, Punjabi – daboia.^[19][15]
• Kashmiri – gunas.^[15]
• Oriya – Chandra Boda
• Sindhi – koraile.^[15]
• Bengali – bora, chandra bora, uloo bora.^[15]
• Gujarati – chitalo, khadchitalo.^[15]
• Marathi – ghonas.^[15]
• Telugu – katuka rekula poda.^[15] or raktha penjara/penjari.
• Kannada – mandaladha haavu^[20] or mandalata havu,^[15] kolakumandala.^[15]
• Tamil – retha aunali, kannadi virian^[15] or kannadi viriyan.^[21]
• Malayalam – mandali, ruthamandali, manchatti, shanguvarayan, "Rakta Anali"^[15]
• Sinhala – thith polonga.^[14][15]
• Burmese – mwe lewe.^[15]
• Tulu – kandhodi

Geographic range

Found in Pakistan, India, Sri Lanka, Bangladesh, Nepal, Myanmar, Thailand, Cambodia, China (Guangxi, Guangdong), Taiwan and Indonesia (Endeh, Flores, east Java, Komodo, Lomblen Islands). The type locality is listed as "India". More specifically, this would be the Coromandel Coast, by inference of Russell (1796).^[1]

Brown (1973) mentions that it can also found in Vietnam, Laos and on the Indonesian island of Sumatra.^[17] Ditmars (1937) reportedly received a specimen from Sumatra as well.^[14] However, the distribution of this species in the Indonesian archipelago is still being elucidated.^[22]

Within its range it can be very common in some areas, but scarce in others.^[13] In India, is abundant in Punjab, very common along the West Coast and its hills, in southern India and up to Bengal. It is uncommon to rare in the Ganga valley, northern Bengal and Assam. It is prevalent in Myanmar.^[15]

Habitat

It 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 (scrub jungles), on forested plantations and farmland. They are most common in plains, coastal lowlands and hills of suitable habitat. Generally 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.^[2]

This species is often found in highly urbanized areas and settlements in the countryside, the attraction being the rodents commensal with man.^[15] As a result, those working outside in these areas are most at risk of being bitten. It should be noted, however, that D. russelii does not associate as closely with human habitation as Naja and Bungarus (cobras and kraits).^[2]

Behavior

Terrestrial and active primarily as a nocturnal forager. However, during cool weather it will alter its behavior and become more active during the day.^[2]

Adults are reported to be persistently slow and sluggish unless pushed beyond a certain limit, after which they become fierce and aggressive. Juveniles, on the other hand, are generally more active and will bite with minimal provocation.^[2]

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.^[2] These are difficult snakes to handle: they are strong and agile and react violently to being picked up.^[10] The bite may be a snap, or, they may hang on for many seconds.^[15]

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.^[23][24] 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.^[25]

Feeding

It feeds primarily on rodents, especially murid species. However, they will eat just about anything, including rats, mice, shrews, squirrels, land crabs, scorpions and other arthropods. Juveniles are crepuscular, feeding on lizards and foraging actively. As they grow and become adults, they begin to specialize in rodents. Indeed, the presence of rodents is the main reason they are attracted to human habitation.^[2]

Juveniles are known to be cannibalistic.^[15]

Reproduction

This species is ovoviviparous.^[13] Mating generally occurs early in the year, although gravid 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,^[2] although there may be fewer offspring and as little as one.^[15] The reported maximum is 65 in a single litter. At birth, juveniles are 215–260 mm in length. The minimum 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 produce 11 young.^[2]

Captivity

These snakes do extremely well in captivity, requiring only a water dish and a hide box. Juveniles feed readily on pinky mice, while the adults will take rats, mice and birds.^[2] However, many adults do not feed, with one having refused all food for five months.^[15] Breeding is not a problem either. On the other hand, they do make quite dangerous captives.^[2] When handled, specimens have been known to use their long, curved fangs to bite right through their lower jaw and into the thumb of the person holding them.^[10]

Venom

The amount of venom produced by individual specimens is considerable. Reported venom yields for adult specimens range from 130–250 mg to 150–250 mg to 21–268 mg. For 13 juveniles with an average length of 79 cm, the average venom yield was 8–79 mg (mean 45 mg).^[2]

The LD₅₀ in mice, which is used as a general indicator of snake venom toxicity, is as follows: 0.08–0.31 μg/g intravenous, 0.40 μg/kg intraperitoneal, 4.75 mg/kg subcutaneous. For most humans a lethal dose is 40–70 mg. In general, the toxicity depends on a combination of five different venom fractions, each of which is less toxic when tested separately. Venom toxicity also varies within populations and over time.^[2]

Envenomation symptoms begin with pain at the site of the bite, immediately followed by swelling of the affected extremity. Bleeding is a common symptom, especially from the gums, and sputum may show signs of blood within 20 minutes post-bite. There is a drop in blood pressure and the heart rate falls. Blistering occurs at the site of the bite, developing along the affected limb in severe cases. Necrosis is usually superficial and limited to the muscles near the bite, but may be severe in extreme cases. Vomiting and facial swelling occurs in about one-third of all cases.^[2]

Severe pain may last for 2–4 weeks. Locally, it may persist depending on the level of tissue damage. Often, local swelling peaks within 48–72 hours, involving both the affected limb and the trunk. If swelling up to the trunk occurs within 1–2 hours, massive envenomation is likely. Discoloration may occur throughout the swollen area as red blood cells and plasma leak into muscle tissue.^[18] Death from septicaemia, respiratory or cardiac failure may occur 1 to 14 days post-bite or even later.^[15]

Because this venom is so effective at inducing thrombosis, it has been incorporated into an in vitro diagnostic test for blood clotting that is widely used in hospital laboratories. This test is often referred to as Dilute Russell's viper venom time (dRVVT). The coagulant in the venom directly activates factor X, which turns prothrombin into thrombin in the presence of factor V and phospholipid. The venom is diluted to give a clotting time of 23 to 27 seconds and the phospholipid is reduced to make the test extremely sensitive to phospholipid. The dRVVT test is more sensitive than the aPTT test for the detection of lupus anticoagulant (an autoimmune disorder), because it is not influenced by deficiencies in clotting factors VIII, IX or XI.^[26]

In India, the Haffkine Institute prepares a polyvalent antivenin that is used to treat bites from this species.^[15]

Subspecies

Subspecies[1]	Taxon author[1]	Common name	Geographic range[2]
D. r. russelii	(Shaw, 1797)	Indian Russell's viper[27]	Across the Indian subcontinent through Pakistan and Bangladesh to Sri Lanka.
D. r. siamensis	(M.A. Smith, 1917)	Eastern Russell's viper[28]	From Myanmar through Thailand, Cambodia, Indonesia and southern China. Also found in Taiwan.[1]

Taxonomy

Using morphological and mitochondrial DNA data, Thorpe et al. (2007)^[29] provided evidence that the eastern subspecies should be considered a separate species, Daboia siamensis

A number of other subspecies may be encountered in literature,^[2] including:

• D. r. formosensis, Maki 1931 – found in Taiwan (considered a synonym of D. r. siamensis).
• D. r. limitis, Mertens 1927 – found in Indonesia (considered a synonym of D. r. siamensis).
• D. r. pulchella, Gray 1842 – found in Sri Lanka (considered a synonym of D. r. russelii).
• D. r. nordicus, Deraniyagala 1945 – found in northern India (considered a synonym of D. r. russelii).

The correct spelling of the species, D. russelii has been, and still is, a matter of debate. Shaw & Nodder (1797), in their account of the species Coluber russelii, named it after Dr. Patrick Russell, but apparently misspelled his name, using only one "L" instead of two. Russell (1727–1805) was the author of An Account of Indian Serpents (1796) and A Continuation of an Account of Indian Serpents (1801). McDiarmid et al. (1999) are among those who favor the original misspelled spelling, citing Article 32c (ii) of the International Code of Zoological Nomenclature. Others, such as Zhao and Adler (1993) favor russellii.^[1]

In the future, more species may be added to Daboia. Obst (1983) reviewed the genus and suggested that it be extended to include Macrovipera lebetina, Vipera palaestinae and V. xanthina. Groombridge (1980, 1986) united V. palaestinae and Daboia as a clade based on a number of shared apomorphies, including snout shape and head color pattern. Lenk et al. (2001) found support for this idea based on molecular evidence, suggesting that Daboia not only include V. palaestinae, but also M. mauritanica and M. deserti.^[2]

Mimicry

Some herpetologists believe that, because D. russelii is so successful as a species and has such a fearful reputation within its natural environment, another snake has even come to mimic its appearance. Superficially, the rough-scaled sand boa, Gongylophis conicus, has a color pattern that often looks a lot like that of D. russelii, even though it is completely harmless.^[14][2]

See also

• List of viperine species and subspecies
• Viperinae by common name
• Viperinae by taxonomic synonyms
• Dilute Russell's viper venom time
• Snakebite

References

Further reading

External links

• Daboia russelii at the Reptarium.cz Reptile Database. Accessed 5 September 2007.
• DRVVT test information at Lab Tests Online. Accessed 5 September 2007.
• Dilute Russell's Viper Venom Time at LabCorp. Accessed 5 September 2007.
• Russell's viper at Naturemagics. Accessed 5 September 2007.
• Russell's Viper at Michigan Engineering. Accessed 5 September 2007.
• Russell's viper at SurvivalIQ. Accessed 5 September 2007.
• When a cobra strikes: Interview with Romulus Whitaker, dated Sunday, June 13, 2004, at The Hindu. Accessed 5 September 2007.
• Mark O'Shea in Sri Lanka at Mark O'Shea. Accessed 5 September 2007.
• Common Poisonous Snakes in Taiwan at Formosan Fat Tire. Accessed 5 September 2007.
• Vipera russelli at Snakes of Sri Lanks. Accessed 5 September 2007.
• Video of Daboia russelii at YouTube. Accessed 5 September 2007.
• Video of Daboia russelii feeding at YouTube. Accessed 5 September 2007.
• Toxicology