“Many venomous members of the family Colubridae are harmless to humans because of small venom glands, weak venom, or inefficient fangs. However, the boomslang is a notable exception in that it has a highly potent venom, which it delivers through large fangs that are located in the back of the jaw. Boomslangs are able to open their jaws up to 170 degrees when biting. The venom of the boomslang is primarily a hemotoxin; it disables the blood clotting process and the victim may well die as a result of internal and external bleeding. The venom causes the victim to bleed from all of the holes in its body. Other signs and symptoms include headache, nausea, sleepiness and mental disorders.
Because the venom is slow to act, symptoms may not be manifested until many hours after the bite. While this provides time for procuring the antivenom, it also may lead victims to underestimate the seriousness of the bite. Snakes of any species may sometimes fail to inject venom when they bite, so after a few hours without any noticeable effects, victims of boomslang bites may believe (wrongly) their injury is not serious.
An adult boomslang has 1.6–8 mg of venom. Various sources give figures ranging from 0.06 – 0.72 mg/kg being sufficient to kill mice in 50% of cases, if the venom reaches a vein (LD50).
In 1957, well-known herpetologist Karl Schmidt died after being bitten by a boomslang. D.S. Chapman stated eight serious human envenomations by boomslangs occurred between 1919 and 1962, two of which were fatal. The South African Vaccine Producers (formerly South African Institute of Medical Research) manufactures a monovalent antivenin for use in boomslang envenomations. Treatment of bites may also require total blood transfusions, especially after 24 to 48 hours without antivenin.
The boomslang is a timid snake, and bites generally occur only when people attempt to handle, catch or kill the animal. When confronted and cornered, they inflate their necks and assume their striking “”S””-shaped pose. The above data suggest boomslangs are unlikely to be a significant source of human fatalities throughout their distribution range.”