(A. Smith, 1829)
Taxonomy and etymology
It is currently the only species in its genus, although several species and subspecies have been described in the past. Its name means "tree snake" in Afrikaans and Dutch – boom meaning "tree" (a cognate of "beam"), and slang meaning "snake". In Afrikaans, the name is pronounced [buˑomslʌŋ]. The snake is thought to be closely related to members of the genera Thelotornis, Thrasops, Rhamnophis, and Xyelodontophis, with which it forms the taxonomic tribe Dispholidini.
The average adult boomslang is 100–160 cm (3¼–5¼ feet) in total length, but some exceed 183 cm (6 feet). The eyes are exceptionally large, and the head has a characteristic egg-like shape. Coloration is very variable. Males are light green with black or blue scale edges, but adult females may be brown.
Weight : Varying from 175 g to 510 g Average weight 299.4 g Teeth : Small, 7 or 8. followed by 3 large grooved fangs situated below the eye, The fangs are 3–5 mm. long, the diameter being nearly 0.5 mm. 
In this species, the head is distinct from the neck and the canthus rostralis is distinct. The pupils of the very large eyes are round. Boomslangs have excellent eyesight and will often move their head from side to side to get a better view of objects directly in front of them. The maxillary teeth are small anteriorly, seven or eight in number, followed by three very large, grooved fangs situated below each eye. The mandibular teeth are subequal. The body is slightly compressed. The dorsal scales are very narrow, oblique, strongly keeled, with apical pits, arranged in 19 or 21 rows. The tail is long, and the subcaudals are paired. Ventrals are 164–201; the anal plate is divided; and the subcaudals are 91–131.
Boomslangs are oviparous, and produce up to 30 eggs which are deposited in hollow tree trunks or rotting logs. The eggs have a relatively long (three months on average) incubation period. Male hatchlings are grey with blue speckles, and female hatchlings are a pale brown. They attain their adult coloration after several years. Hatchlings are approximately 20 cm in length and pose no threat to humans, but are dangerously venomous by the time they reach a length of about 45 cm and a girth as thick as an adult's smallest finger.
Behavior and diet
Boomslangs are diurnal and almost exclusively arboreal. They are reclusive, and will flee from anything too large to eat. Their diet includes chameleons and other arboreal lizards, frogs, and occasionally small mammals, birds, and eggs from nesting birds, all of which they swallow whole. During cool weather, they will hibernate for moderate periods, often curling up inside the enclosed nests of birds such as weavers.
Many venomous members of the family Colubridae are harmless to humans because of small venom glands and 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 has been observed to cause hemorrhage into tissues such as muscle and brain. 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 wrongly believe that their injury is not serious.
In 1957, well-known herpetologist Karl Schmidt died after being bitten by a juvenile boomslang which he doubted could produce a fatal dose, so he administered no antivenom. Unfortunately, he was wrong; nevertheless, he made notes on the symptoms he experienced almost right up to the end. 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 antivenom.
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.
In popular culture
- The venom of the boomslang also features in the Agatha Christie thriller, Death in the Clouds (pub.1935), featuring her famous detective, Hercule Poirot.
- In the Stephen King short story "Autopsy Room 4" from "Everything's Eventual" the main character is paralyzed as the result of a boomslang bite.
- In the Harry Potter books the skin of a boomslang is described as being an ingredient for the Polyjuice Potion
- Boulenger, G.A. 1896. Catalogue of the Snakes in the British Museum (Natural History), Volume III. London. pp. 186–189.
- Encyclopædia Britannica. Encyclopædia Britannica, Inc. 2007.
- Oxford English Dictionary. Oxford, England: Oxford University Press. 1989.
- Broadley, Donald; Wallach, Van (November 2002). "Review of the Dispholidini, with the description of a new genus and species from Tanzania (Serpentes, Colubridae)". Bull. Nat. Hist. Mus. Lond. (Zool.) 68 (2): 57–74. doi:10.1017/S0968047002000079.
- Studies on the Venom of the Boomslang S.A. Medical Journal June 22, 1940 by E. Grassy M.D.
- Johan Marais: A Complete Guide To The Snakes Of southern Africa, Struik, 2nd edition, 2004
- Kamiguti, AS; Theakston RD; Sherman N; Fox JW (November 2000). "Mass spectrophotometric evidence for P-III/P-IV metalloproteinases in the venom of the boomslang (Dispholidus typus)". Toxicon 38 (11): 1613–1620. doi:10.1016/S0041-0101(00)00089-1. PMID 10775761.
- LD50 for various snakes
- Stephen P. Mackessy: Biochemistry and Pharmacology of Colubrid Snake Venoms. J. Toxicol. – Toxin Reviews 21 (1&2), 2002: page 52 online PDF
- Smith, Charles H.. "Chrono-Biographical Sketch: Karl P. Schmidt". Some Biogeographers, Evolutionists and Ecologists. Retrieved 9 September 2014.
- Boomslang (Dispholidus typus)
- Boomslang vs.Chameleon NatGeo
- Boomslang predation on Sabota Lark nest (with video)
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