Boomslang
Template:Short description {{#invoke:other uses|otheruses}} Template:Speciesbox
The boomslang (Template:IPAc-en or Template:IPAc-en; Dispholidus typus) is a highly venomous snake in the family Colubridae.<ref name=eb>Template:Cite book</ref> The species is native to Sub-Saharan Africa.
EtymologyEdit
Its common name means "tree snake" in Dutch<ref name=oed>Template:Cite book</ref> and Afrikaans – boom meaning "tree", and slang meaning "snake". In Afrikaans, the name is pronounced {{#invoke:IPA|main}}.
TaxonomyEdit
The boomslang is a colubrid snake within the subfamily Colubrinae. It belongs to the genus Dispholidus, which contains two other species, D. pembae and D. punctatus.
The boomslang is thought to be closely related to members of the genera Thelotornis, Thrasops, Rhamnophis, and Xyelodontophis, with which it forms the taxonomic tribe Dispholidini.<ref name=te>Template:Cite journal</ref>
Close relationships can be shown in the cladogram below:<ref name="Figueroa2016">Template:Cite journal</ref> Template:Clade
SubspeciesEdit
Two subspecies are recognised, including the nominotypical subspecies.<ref>Template:EMBL species. www.reptile-database.org.</ref>
- D. t. kivuensis Template:Small
- D. t. typus Template:Small
The trinomial authority in parentheses for D. t. typus indicates that the subspecies was originally described in a genus other than Dispholidus.
DescriptionEdit
The average adult boomslang is Template:Convert in total length (including tail). Some exceed Template:Convert. The eyes are exceptionally large, and the head has a characteristic egg-like shape. Colouration is highly variable. Males are light green with black or blue scale edges, but adult females may be brown demonstrating sexual dimorphism.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Weight varies from Template:Convert, with an average weight of Template:Convert.<ref>Grassy E MD (June 22, 1940). "Studies on the Venom of the Boomslang". South African Medical Journal.</ref>
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 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, 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.<ref name=Blgr96/>
Geographic rangeEdit
The boomslang is endemic to Sub-Saharan Africa, from The Gambia, Guinea, Senegal and most of Western Africa (including Benin, Cameroon, Ghana, Nigeria, Togo)<ref name=":0" /> through Central and Eastern 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.<ref name=":0">{{#invoke:citation/CS1|citation
|CitationClass=web }}</ref>
HabitatEdit
The boomslang is an excellent climber and is highly arboreal, living mainly in forested areas. D. typus lives in karoo shrubs, savannahs, 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
ReproductionEdit
The boomslang is oviparous, and an adult female can produce up to 30 eggs, which are deposited in a hollow tree trunk or rotting log. The eggs have a relatively long (3 months on average) incubation period. Male hatchlings are grey with blue speckles, and female hatchlings are pale brown. They attain their adult colouration after several years. Hatchlings are about Template:Convert in length and pose no threat to humans, but are dangerously venomous by the time they reach a length around Template:Convert and a girth as thick as an adult's smallest finger.
Behaviour and dietEdit
D. typus is diurnal and almost exclusively arboreal. It is reclusive, and moves from branch to branch when pursued by anything too large to eat. Its diet includes chameleons and other arboreal lizards,<ref name=eb/> frogs, and occasionally small mammals, birds, and eggs from nesting birds and reptiles,<ref name=eb/><ref name=ADW>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> all of which it swallows whole. The boomslang will also feed on other snakes, including cannibalising members of its own species.<ref name=ADW/> During cool weather, the boomslang brumates for short periods, often curling up inside the enclosed nest of a weaverbird.
VenomEdit
Many venomous species of the Colubridae are harmless to humans—unless one has a known rare allergy—largely because of small venom glands and inefficient teeth that are situated at the back of the mouth. These species, including the boomslang, are collectively known as "rear-fanged" (or opisthoglyphous) snakes, as their venom-injecting teeth are situated farther back in the mouth than elapids or vipers, and thus require the snake to bite, hold-on, and "chew" the venom into its victim.
However, some opisthoglyphous snakes—including the boomslang—actually possess a highly potent and toxic venom.<ref name="eb" /> The boomslang is able to open its jaws up to 170° when biting, facilitating envenomation.<ref>Marais, Johan (2004). A Complete Guide to the Snakes of Southern Africa. Second Edition. Struik.</ref> The venom of the boomslang is primarily a hemotoxin; it works via a process in which many small clots 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 capillaries with tiny blood clots.<ref name="eb" /><ref>Template:Cite journal</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Its median lethal dose (LD50) in mice is 0.1 mg/kg (intravenously).<ref>Mackessy, Stephen P. (2002). "Biochemistry and Pharmacology of Colubrid Snake Venoms". Journal of Toxicology – Toxin Reviews 21 (1&2): 52. online PDF Template:Webarchive</ref> 0.071 mg/kg (IV) has also been reported.<ref>Template:Cite journal</ref> 12.5 mg/kg (subcutaneously) and 1.3–1.8 mg/kg (intraperitoneal).<ref>Template:Cite journal</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
In 1957, herpetologist Karl Schmidt died after being bitten by a juvenile boomslang, which he had doubted could produce a fatal dose.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> He made notes on the symptoms he experienced almost to the end.<ref name="Pope-1958">Template:Cite journal</ref><ref name=ChronoSketch>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> D. S. Chapman reported eight serious envenomations by boomslangs between 1919 and 1962, two of which were lethal.<ref>Bücherl W, Buckley E, Deulofeu V (editors) (1968). Venomous Animals and Their Venoms, Volume I: Venomous Vertebrates. Academic Press. p. 484. </ref>
Boomslang monovalent antivenom was developed during the 1940s. The South African Vaccine Producers manufactures a monovalent antivenom for use in boomslang envenomations.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.
GalleryEdit
- MaleBoomslang.jpg
A male boomslang
- Boomslang - Western Cape.jpg
Boomslang in Western Cape, South Africa
- Common Boomslang1.jpg
Juvenile common boomslang (Dispholidus t. typus)
- Common Boomslang3.jpg
Brown female common boomslang (Dispholidus t. typus)
- Illustrations of the zoology of South Africa (6263858468).jpg
Illustration of D. typus (named as Bucephalus viridis).
ReferencesEdit
Further readingEdit
- Access Professional Development. 2022. Boomslang (Dispholidus typus). [Online] Available: https://accesspd.co.za/species/Boomslang Template:Webarchive (Accessed: 02/02/2022)
- Branch, Bill (2004). Field Guide to Snakes and other Reptiles of Southern Africa. Third Revised edition, Second impression. Sanibel Island, Florida: Ralph Curtis Books. Template:ISBN. (Dispholidus typus, pp. 99–100 + Plate 31).
- Goin CJ, Goin OB, Zug GR (1978). Introduction to Herpetology, Third Edition. San Francisco: W.H. Freeman. Template:ISBN. (Dispholidus typus, pp. 322, 324.)
- Laurent RF (1955). "Diagnoses preliminaires des quelques Serpents venimeuxTemplate:-" Template:In lang. Revue de zoologie et de botanique africaines 51: 127–139. (Dispholidus typus kivuensis, new subspecies; D. t. punctatus, new subspecies.)
- Smith A (1828). "Descriptions of New or Imperfectly Known Objects of the Animal Kingdom, Found in the South of Africa". South African Commercial Advertiser 3 (144): 2. (Bucephalus typus, new species.)