Hump-nosed viper

Identification

The hump-nosed viper is a small, stout pit viper with a flat, triangular head that is broader than its neck⁷. Its snout is pointed and turned up at the end, which gives it a Sinhala name meaning “viper with an upturned lip”, and like other pit vipers it has a heat-sensing pit between the nostril and the eye^3,4,5.

It is greyish or brownish above, heavily mottled, with a row of large dark spots on each side of the back and keeled body scales^1,3. A dark stripe runs back from the eye with a pale one above it, and the tip of the tail is often yellowish or reddish³.

Smith (1943) gave total lengths of 33 cm for a male and 48 cm for a female³. A recent account describes it as a fairly small snake of less than 0.6 m⁷.

Distribution

The hump-nosed viper lives in Sri Lanka and in the Western Ghats of south-western India, in Kerala, Karnataka and Tamil Nadu¹. In India it reaches north to about latitude 16° N, and it has been studied in the Western Ghats of Goa^3,6.

A 2009 revision showed that two other hump-nosed vipers are found only in Sri Lanka: H. nepa in the central mountains and H. zara in the south-western lowlands².

Habitat

It lives in evergreen, moist and dry deciduous forests and in human-modified areas such as plantations⁷. In Goa it was found mostly on the ground beneath leaf litter, in cane and bamboo thickets and in semi-evergreen and moist deciduous forest, from about 35 m to 670 m above sea level⁶. There it moved into neighbouring cashew plantations after the monsoon, and it seems to prefer cool, moist places⁶.

In Sri Lanka, people are usually bitten by this species in home gardens⁴.

Behaviour

The hump-nosed viper is well camouflaged, moves very little and hunts by ambush⁶. It is mostly terrestrial but sometimes climbs into low bushes and herbs^3,6. It has been watched hunting at about 10 pm⁷. In one large Sri Lankan study most people were bitten at night near their homes, but another found that most bites happened during the day⁴.

In Goa it was most abundant during the monsoon⁶.

Diet

It eats small mammals such as rodents, lizards including geckos and skinks, and frogs⁷. In Karnataka, one was seen ambushing a skink at night; the skink died within about 40 seconds of the bite⁷.

Young hump-nosed vipers wriggle their pale tail tips like worms to lure lizards within striking range^3,7.

Reproduction

The hump-nosed viper gives birth to live young^1,3. A litter contains about four to ten young³.

Venom and medical significance

The hump-nosed viper was long thought to cause only local effects, but it is now known to cause serious systemic poisoning and occasional deaths⁴. Pain and swelling occur in about 90% of envenomed people and can lead to blistering and tissue death, and some develop blood-clotting problems or acute kidney injury that can become long-term kidney disease⁴.

In a ten-hospital study in Sri Lanka, it caused 35% of bites by identified snakes, and 1.7% of those bitten died, all from kidney failure⁴. The World Health Organization places it in its highest category of medical importance in Sri Lanka and south-western India⁵.

The polyvalent antivenoms made in India are raised against the “big four” snakes and do not cover this species, and in Sri Lanka the available polyvalent antivenom has proved ineffective against its bites and often causes reactions^4,5. Anyone bitten should go to hospital immediately.

Conservation

The hump-nosed viper is listed as Least Concern on the IUCN Red List (2021 assessment)⁸. It was the most abundant of three pit vipers counted in a survey of Goa’s wildlife sanctuaries⁶. In India it is protected under Schedule II of the Wild Life (Protection) Act, which covers all vipers not listed in Schedule I⁹.

Similar species

Its bites have been mistaken for those of the saw-scaled viper (Echis carinatus) in south-western India and of Russell’s viper (Daboia russelii) in Sri Lanka, leading to unnecessary antivenom treatment⁵. Both of those are true vipers without the heat-sensing pit between the nostril and the eye that the hump-nosed viper has⁵. Russell’s viper also has rows of large, dark-rimmed spots along its body⁵.

In Sri Lanka, H. nepa has a wart-like bump at the tip of its snout, and H. zara has a distinctly raised snout tip¹. These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The hump-nosed viper is a venomous snake whose bite can cause kidney failure, and it is not suitable as a pet⁴. In India it is protected under Schedule II of the Wild Life (Protection) Act, as amended in 2022⁹. It should never be caught or kept by private individuals.