Drop for drop, the Boomslang (Dispholidus typus) probably has the most potent venom of any snake in Africa. Where the Black mamba produces more than 300 mg of venom and needs around 15 mg of venom to inflict a lethal bite on an adult, the Boomslang has around 8 mg of venom and needs around 0.025 mg for a lethal bite – so small a drop that one cannot see it with the naked eye.
 

The problem with studies on venoms is that the potency of snake venom is tested in an LD50 test – the amount of venom that is needed to kill fifty out of 100 laboratory mice within a period of 24 hours. It tells us little about the effect of venoms on people, but from case studies we know that Boomslang venom is extremely potent. It is a slow-acting haemotoxic venom that may take anything from about 4 – 30 hours before the first symptoms of envenomation are detected. It usually starts with bleeding from the fang punctures followed by a nosebleed, severe headache, bleeding from the mucous membranes and eventually internal bleeding. In untreated serious bites it may take a day or two for human victims to succumb.

The fangs of a Boomslang are situated under the eyes and quite far back in the mouth, and are up to 5mm in length.  
 

Fortunately, the Boomslang is a placid snake that lives in trees and shrubs, is quick to escape and rarely bites. Less than half a dozen Boomslang bites are recorded in South Africa every year and victims are those that accidentally stand on a Boomslang or attempt to handle one. Snake removers occasionally get bitten, especially when grabbing a small individual. 
 

The South African Vaccine Producers, who are part of our National Health Laboratories, produce a highly effective monovalent Boomslang antivenom. It is packaged in a 10 ml vial, costs R6 800 per vial and most patients need two vials. If injected early, it is highly effective.
 

SAVP produces a Monovalent Boomslang Antivenom. 

Boomslang hatchlings measure 29-38 cm in length and are grey-brown in colour and boast a large head with a massive emerald green eye. When they reach a length of close on 1 meter, they gradually change to the adult colours. Over much of their range, most male Boomslang are green in colour, sometimes with black-edged scales, giving them a checkered effect. Females are usually grey to brown in colour but not always. We occasionally see a green Boomslang laying eggs. That said, in the Western and most of the Eastern Cape, males are blackish above with yellow or green sides while the females are brown. In some parts of the Eastern Cape, and further north in Africa, we occasionally see red females.

Green Boomslang are often mistaken for the Green Mamba but differ in that the Boomslang has keeled body scales and a very large eye, whereas the Green Mamba has smooth body scales. Also bear in mind that the Green Mamba is largely restricted to coastal KwaZulu-Natal in South Africa or tropical savannah and evergreen forest in East Africa. 

Boomslang have a variety of colours: brown female (top left), Cape male (top right), northern male (bottom left) and a typical juvenile (bottom right). 
 

This snake may be found in Karoo scrub, arid savanna, moist savanna, lowland forest, grassland or fynbos – provided there are trees or shrubs. It is a diurnal snake that may descend to the ground to bask or hunt but prefers to be well off the ground. Tree-living snakes, including the Boomslang, have superior vision and have no difficulty locating prey. When it does, the Boomslang freezes with its head cocked, the only movement being lateral waves that sweep the neck. It quickly swoops onto its prey which it holds firmly in its jaws while the fangs move with a chewing action. Back-fanged snakes have Duvernoid’s glands that differ somewhat from the venom glands of cobras and mambas – these snakes have far less control over their venom glands and the chewing action enables better envenomation.
 

A young Boomslang raiding a weaver bird's nest.

Finding Boomslang in the wild is not easy and the only give-away is usually the distress calls of birds. The bulbuls are often the first ones to emit their distress calls while perching close to the snake and staring at it. Then follows the white-eyes, sunbirds, barbets and eventually a variety of birds join in. It seems that they feel safer if they can see the snake rather than to just fly off. Despite their placid nature, a Boomslang may inflate its neck massively when threatened and eventually most of the body will be inflated as well. At this stage the snake will draw its head back into an s-shape and strike readily and repeatedly. 
 

An agitated female Boomslang with the throat inflated.