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The boomslang ( or ; Dispholidus typus) is a highly snake in the family Colubridae. The species is native to Sub-Saharan Africa.
The boomslang is thought to be closely related to members of the genus Thelotornis, Thrasops, Rhamnophis, and Xyelodontophis, with which it forms the taxonomic tribe Dispholidini.
Close relationships can be shown in the cladogram below:
The Trinomen in parentheses for D. t. typus indicates that the subspecies was originally described in a genus other than Dispholidus.
Weight varies from , with an average weight of .Grassy E MD (June 22, 1940). "Studies on the Venom of the Boomslang". South African Medical Journal.
In this species, the head is distinct from the neck and the canthus rostralis is distinct. The pupil of the very large eye is round. The boomslang has excellent eyesight and often moves its head from side to side to get a better view of objects directly in front. The maxillary tooth 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, which are arranged in 19 or 21 rows, are very narrow, oblique, strongly keeled, with apical pits. The tail is long, and the subcaudal scales are paired. Ventral scales are 164–201; the anal plate is divided; and the subcaudals are 91–131.
The boomslang snake possess a highly potent and toxic venom. The boomslang is able to open its jaws up to 170° when biting, facilitating envenomation. (2004). A Complete Guide to the Snakes of Southern Africa. Second Edition. Struik. The venom of the boomslang is primarily a hemotoxin; it works via a process in which many small Coagulation form in the blood, causing the victim's circulatory system to improperly coagulate, resulting in excessive bleeding and death. The venom has been observed to cause bleeding in tissues such as muscle and the brain (among other organs), while, at the same time, clogging Capillary with tiny blood clots. Other signs and symptoms include headache, nausea, sleepiness, and confusion, leading to cardiac arrest and unconsciousness.
Because boomslang venom is slow-acting, symptoms may not become apparent until many hours after a bite. Although the absence of symptoms provides sufficient time for procuring antivenom, it can also provide victims with false reassurances, leading to underestimation of the seriousness of the bite. Snakes of any species may sometimes fail to inject venom when they bite (a so-called "dry bite" or "bluff strike", enacted in-defense), wherein, after a few hours without any noticeable effects, victims of boomslang bites may falsely believe that their attack was simply a dry or bluff strike. The pathophysiological mechanisms of the venom are different with every snake, resulting in different clinical manifestations with every patient.
An adult boomslang has 1.6 to 8 mg of venom. Its median lethal dose (LD50) in mice is 0.1 mg/kg (intravenously).Mackessy, Stephen P. (2002). "Biochemistry and Pharmacology of Colubrid Snake Venoms". Journal of Toxicology – Toxin Reviews 21 (1&2): 52. online PDF 0.071 mg/kg (IV) has also been reported. 12.5 mg/kg (subcutaneously) and 1.3–1.8 mg/kg (intraperitoneal). Based on the very low venom quantities produced by D. typus, and the very serious effects found in a good part of the reported cases in humans, it has been suggested that the venom's LD50 is lower in humans than in mice, with only 2 to 3 mg being enough to potentially kill a healthy adult.
In 1957, herpetology Karl Schmidt died after being bitten by a juvenile boomslang, which he had doubted could produce a fatal dose. He made notes on the symptoms he experienced almost to the end. D. S. Chapman reported eight serious by boomslangs between 1919 and 1962, two of which were lethal.Bücherl W, Buckley E, Deulofeu V (editors) (1968). Venomous Animals and Their Venoms, Volume I: Venomous Vertebrates. Academic Press. p. 484.
Boomslang snake antivenom was developed during the 1940s. The South African Vaccine Producers manufactures a monovalent antivenom for use in boomslang envenomations. Treatment of bites may also require complete blood transfusions, especially if over 24-48 hours have passed without antivenom.
The boomslang is a timid snake, and bites generally occur only when people attempt to handle, catch, pursue or kill the animal. When confronted and cornered, it inflates its neck and assumes an S-shaped striking pose, a key indicator of any snake species feeling threatened.
Geographic range
boomslang is Endemism to Sub-Saharan Africa, from The Gambia, Guinea, Senegal and most of West Africa (including Benin, Cameroon, Ghana, Nigeria, Togo) through Central Africa and East Africa (Democratic Republic of the Congo, western Ethiopia, Kenya, South Sudan, Tanzania, Uganda). It is found across much of Southern Africa, in a wide array of habitats, with some of the species' densest populations being in Angola, Botswana, Eswatini, Malawi, Mozambique, Namibia, South Africa, Zambia and Zimbabwe.
Habitat
The boomslang is an excellent climber and is highly arboreal, living mainly in forested areas. D. typus lives in karoo shrubs, , lowland forests, and in grasslands. The boomslang is not restricted to trees and can often be found on the ground hunting, feeding, or taking shelter. It will occasionally hide underground when the weather is harsh.
Reproduction
The boomslang is oviparous, and an adult female can produce on average, 8 to 14 leathery eggs and up to 27 have been observed, which are deposited in a hollow tree trunk or rotting log. The eggs have a relatively long (3 months on average) incubation period. Male are grey with blue speckles, and female hatchlings are pale brown. They attain their adult colouration after several years. Hatchlings are about to in length and pose no threat to humans, but are dangerously venomous by the time they reach a length around and a girth as thick as an adult's smallest finger.
Behaviour and diet
D. typus is diurnality and almost exclusively arboreal. It is reclusive, and moves from branch to branch when pursued by anything too large to eat. Its diet includes and other arboreal , , and occasionally small , , and eggs from nesting birds and reptiles, all of which it swallows whole. The boomslang will also feed on other snakes, including cannibalising members of its own species. During cool weather, the boomslang brumates for short periods, often curling up inside the enclosed bird nest of a Ploceidae.
Venom
The Colubridae are collectively known as "rear-fanged" (or opisthoglyphous) snakes, as their venom-injecting teeth are situated farther back in the mouth than Elapidae or Viperidae, and thus require the snake to bite, hold-on, and "chew" the venom into its victim.
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Further reading
(Accessed: 02/02/2022)
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