Boomslang

Identification

The boomslang is a long, slender snake with heavily keeled scales that give its body a rough look^6,14. It has a short, egg-shaped head and very large eyes, said to be the largest of any snake in Africa^6,7,8. Most adult males are bright green, but in the Western Cape and much of the Eastern Cape many are black above with yellow or greenish sides, and females are usually brown or olive-brown^4,6.

Young boomslangs are grey to brown above with a yellow to orange throat and a huge emerald-green eye, and they change to adult colours at about 1 m long^4,6. Adults average about 1.3 m⁸, and the largest reach around 2.3 m⁶.

Distribution

The boomslang lives across much of sub-Saharan Africa¹. The Reptile Database lists it from Senegal and Gambia in the west to Sudan, Eritrea, Ethiopia and Somalia in the east, and south through East and Central Africa to Angola, Namibia, Botswana, Zimbabwe, Mozambique, Eswatini and South Africa¹. Old reports from Gabon are thought to be mistakes¹. In southern Africa it is widespread but avoids the dry, treeless west⁶.

The Reptile Database now treats the spotted boomslang of Angola, the Democratic Republic of the Congo, Zambia and Malawi as a separate species, Dispholidus punctatus², and the boomslang of Pemba Island, Tanzania, as Dispholidus pembae³.

Habitat

The boomslang uses a wide range of habitats, including lowland forest, savanna, grassland, fynbos and Karoo scrub⁸. It is mainly a tree snake and is usually found in trees or small shrubs^4,8. It comes down to the ground to bask or to catch prey^4,6. Within its habitats it tends to favour the moister areas and avoids very dry, desert-like country⁷.

Behaviour

The boomslang is active by day⁷. It is shy and very reluctant to bite, and in a tree it poses little threat to people⁴. If spotted, it usually moves quickly higher into the branches⁵. When threatened it inflates its neck to look bigger and opens its mouth^7,8. Most bites happen when a basking snake is stepped on or grabbed by accident, or when someone handles it⁵.

Diet

Boomslangs feed mainly on chameleons and other tree lizards, and also take nestling birds and eggs¹. Frogs are eaten too^7,8. Like other back-fanged snakes, the boomslang hangs onto its prey while venom runs down grooves in fangs at the back of its mouth¹³.

Reproduction

The boomslang lays eggs¹. Unlike most snakes, it can mate in trees as well as on the ground^7,8. A female usually lays 8 to 14 eggs in late spring or early summer, in an old bird’s nest or on the ground near a tree⁸. Clutches of up to 27 eggs have been recorded⁷. The eggs hatch after about two to three months, and the hatchlings measure about 29–38 cm⁷.

Venom and medical significance

The boomslang is rear-fanged, but it can open its jaws to about 170 degrees and easily bite an arm or a leg¹³. Its haemotoxic venom uses up the blood’s clotting factors, so the blood stops clotting and bleeding can follow from the bite, the gums, the nose and inside the body^5,9,10. Symptoms usually appear 6 to 36 hours after a bite, so a person may feel well at first, although a young man in the Northern Cape who was bitten twice died within about eight hours⁹.

Bites are uncommon: in a five-year review at one KwaZulu-Natal hospital, only four of 879 snakebite patients needed boomslang antivenom⁹. The World Health Organization ranks the boomslang as a snake of secondary medical importance (Category 2) in many African countries, including South Africa and Kenya, and a specific monovalent antivenom is made for its bites by the South African Vaccine Producers (SAVP)^5,11,12. Anyone bitten should go to hospital immediately, even if they feel well.

Conservation

The boomslang is listed as Least Concern on the IUCN Red List (2021 version)¹⁶. It has a very large range across sub-Saharan Africa¹ and is widespread in southern Africa⁶.

Similar species

A brown female boomslang can be confused with a black mamba (Dendroaspis polylepis), which has smooth scales, a long coffin-shaped head, dark eyes and a black mouth lining, unlike the boomslang’s rough scales, short head and large eyes¹⁴. A green boomslang can be mistaken for a green mamba (Dendroaspis angusticeps), which has a long, coffin-shaped head and lacks the small loreal scale between the nostril and the eye that boomslangs have⁶. Harmless green bush snakes (Philothamnus) are smaller, and any green snake under 80 cm is very unlikely to be a boomslang, while young boomslangs are easily confused with twig snakes, which have also caused deaths^6,13,15.

These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The boomslang is a dangerous venomous snake⁴ and is not suitable as a pet. Many bites happen to people who handle or catch the snake^5,8. The herpetologist Karl P. Schmidt died after a bite from a young boomslang, when the species was thought to be only mildly venomous^1,13. He kept notes on his symptoms as he was dying¹.