White-lipped pit viper

Identification

The white-lipped pit viper is bright green on the back and sides, with yellow lips and a yellow side of the neck³. The belly is yellowish^1,3, and the top of the tail is reddish brown^3,5. Males have a thin pale line along the lower edge of each side^1,3. The head is broad and strongly triangular, covered in small granular scales, and has a heat-sensing pit between the eye and the nostril³. The eyes are orange-yellow with vertical, slit-like pupils, and the body scales are moderately keeled³.

In Hong Kong, adults average about 0.5 m long and can reach about 0.9 m³. Females grow larger than males¹.

Distribution

The white-lipped pit viper lives in southern China (including Hainan, Hong Kong and Macau), Myanmar, Thailand, Laos, Cambodia, Vietnam and western Indonesia, including Sumatra and western and central Java^1,2. Records from Borneo and Sulawesi are uncertain, and it is no longer considered to occur in India¹.

The species was once treated much more broadly. The white-lipped island pit viper of the Lesser Sunda Islands (T. insularis) and the northern white-lipped pit viper of the Himalayan foothills (T. septentrionalis) are now separate species^1,2,5. A 2025 revision recognised three subspecies: T. a. albolabris in China and far north-eastern Vietnam, T. a. fario in the lowlands of southern Thailand, Cambodia, southern Vietnam and western Java, and T. a. guoi in Yunnan, northern Vietnam, northern Thailand and Myanmar^1,2.

Habitat

This pit viper lives in many kinds of open and disturbed country^2,3. In Hong Kong it is found at all altitudes and is especially common on low hills with shrubland and grassland and at the edges of farmed fields, but it is rare in dense forest and absent from towns, fish ponds and mangroves³. Elsewhere it has been found in swamp forest and grassland in Cambodia, and in secondary forest, plantations and farmland in Java and southern Thailand². It seems to adapt well to living near people².

Behaviour

It is mainly active at night³. The heat-sensing pits let it find and strike warm-blooded prey accurately even in total darkness³. It climbs into bushes and small trees, but is often found on low plants or on the ground^2,3. Like most snakes, it does not attack people unless it is disturbed⁶.

Diet

The white-lipped pit viper eats mammals, frogs and lizards, and occasionally small birds³. Its heat-sensing pits help it to find warm-blooded prey such as mammals and birds in the dark³.

Reproduction

This pit viper gives birth to live young^1,3. In Hong Kong, pairing takes place in May and the young are born about two months later³. An average litter has about 12 young, each 15–20 cm long at birth³.

Venom and medical significance

The white-lipped pit viper is a common cause of snakebite. It accounts for about 95% of venomous snakebites treated in Hong Kong⁴, and in 2017 it caused 92% of 267 snakebites treated in hospitals in Can Tho, in Vietnam’s Mekong Delta². WHO lists it among the snakes of highest medical importance in Indonesia and Myanmar⁵.

A bite is painful and causes marked swelling³. The venom can also stop the blood from clotting properly, sometimes with bleeding, and this can be life-threatening⁴. Deaths are rare: in Hong Kong the last reported death was in 1986⁴, and none of the 267 patients in the Can Tho study died². Specific green pit viper antivenoms are made in Thailand and Vietnam and can correct the clotting problem^2,4,5. Anyone bitten should go to hospital immediately.

Conservation

The white-lipped pit viper is listed as Least Concern on the IUCN Red List (assessed in 2012)⁷. It is Hong Kong’s most common venomous snake³.

Similar species

The harmless greater green snake (Cyclophiops major) of southern China looks similar, but it is slender, with mostly smooth, glossy scales and a less triangular head, and it is active by day⁸. The spot-tailed green pit viper (Trimeresurus erythrurus) has a brown-spotted tail and keeled scales on the sides of the head, while the white-lipped pit viper has a plain brown-topped tail and smooth scales there⁵. In East Java and the Lesser Sundas, the white-lipped island pit viper (T. insularis) takes its place². These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The white-lipped pit viper is a venomous snake and is not suitable as a pet. In Hong Kong, the authorities advise people never to try to catch a snake, and to call 999 if one enters a house⁶. It should never be caught or kept by private individuals.