Long, arboreal and often dazzlingly green, the boomslang looks more like a vine with eyes than a killer. Yet this member of the Colubrid snake family carries an incredibly potent venom, capable of causing catastrophic internal bleeding.
It is shy and much less likely to bite than some other more aggressive venomous snakes, such as the saw-scaled viper, but when it does, the consequences can be horrifying, causing the body to come apart from within.
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Where does the boomslang snake live?
The boomslang, Dispholidus typus, is common across much of sub-Saharan Africa. It is a snake of trees and thickets, occurring in habitats such as savanna, shrubland, lowland forest and grassland.
Much of its life is spent above ground in branches, where its slender body and superb camouflage make it hard to spot. The name ‘boomslang’ means ‘tree snake’ in Afrikaans. It will descend to bask and hunt and may retreat underground in inclement weather.
How big is it?
This lightly built snake usually grows to around 1-1.6m long, though large individuals can approach 2m.
What does the boomslang snake look like?
It has a blunt head, a very long tail and unusually large eyes, giving it a keen, watchful look. Its colouring is famously variable. Males can be vivid green, black, yellow-and-black or russet, while females tend to be a duller olive-brown or grey. Juveniles are grey or brown, often with especially striking green eyes.
What does it eat?
The boomslang is a daytime hunter that preys chiefly on small animals moving through trees and shrubs. Birds and nestlings feature prominently in its diet, but it also takes frogs, lizards and, more occasionally, small mammals.
How does the boomslang hunt?
The boomslang is an ambush predator of extraordinary patience. A boomslang may remain motionless for long periods, stretched along a branch or half-hidden in foliage, waiting for prey to wander within reach. Some observers describe it swaying gently like a twig in the breeze before striking. Its huge eyes help it pick out movement among leaves and branches.
Why is its venom so deadly?
Because it turns the victim’s own blood against them. Boomslang venom is powerfully haemotoxic, wrecking the body’s clotting system so that bleeding cannot be brought under control. At first, a bite may not seem dramatic.
There may be little pain, and the person may even feel well enough to dismiss it. Hours later, though, the damage can begin to declare itself: blood seeping from the gums and nose, bruising spreading under the skin, blood appearing in vomit, urine or stools, and internal haemorrhaging gathering pace out of sight.
In other words, this is a snake that can leave its victim bleeding from the inside out. Antivenom can be highly effective, but speed matters.
How does a rear-fanged snake manage to kill people?
Rear-fanged does not mean harmless. The boomslang’s fangs sit farther back in the mouth than those of vipers or cobras, but they are positioned far enough forward to be highly effective, and the snake can open its jaws extremely wide.
A firm bite can therefore deliver a dangerous dose of venom. The African Snakebite Institute reports that the boomslang needs only around 0.025mg of venom for a lethal bite on an adult, whereas the black mamba, for instance, needs around 15mg of venom.
The old assumption that rear-fanged snakes could not kill people was shattered in 1957, when the respected herpetologist Karl P. Schmidt died after being bitten by a juvenile boomslang and recording his worsening symptoms as the venom took hold.
Believing, wrongly, that a rear-fanged species of that size could not inject a lethal dose, he tragically did not seek the treatment that might have saved him. Few snakebite cases have left such a chilling record, and few have done more to destroy the myth that rear-fanged snakes are harmless.
Does it attack humans?
No – at least, not in the melodramatic way snake lore suggests. The boomslang is generally described as shy, and bites are very rare. Most happen when people try to catch, handle, pursue or kill the snake.
When threatened, however, it can become spectacularly defensive: inflating the neck to show the dark skin between the scales, forming a striking posture and then lashing out if pressed. The danger lies not in aggressiveness, but in the fact that a reluctant bite can still be lethal.
How does it breed?
In the breeding season, females leave scent trails that males follow, and rival males may wrestle for access to a mate. The boomslang is egg-laying and females lay around 8-27 eggs in a sheltered, damp place such as a hollow tree or old burrow. After roughly 65-100 days, the young hatch already armed with fangs and venom. Even at that stage, they are not to be underestimated.
Why does it matter beyond its shock value?
Partly because it is a beautifully adapted predator, helping to regulate populations of birds, reptiles and other small animals in the ecosystems it inhabits. But also because it is a useful corrective to lazy ideas about dangerous snakes.
The boomslang is not thick-bodied, noisy or openly intimidating. It is almost dainty, watchful and often very beautiful. Its horror lies in the contrast between appearance and effect: a slender snake in the branches whose bite can leave a body quietly filling with blood.
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Top image: Craig Cordier / Getty Images
