The boomslang (, , or ; ''Dispholidus typus'') is a large, highly

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a ...

ous

snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...

in the family

Colubridae Colubridae (, commonly known as colubrids , from la, coluber, 'snake') is a family of snakes. With 249 genera, it is the largest snake family. The earliest species of the family date back to the Oligocene epoch. Colubrid snakes are found on ev ...

Taxonomy and etymology

Its common name means "tree snake" in

Afrikaans Afrikaans (, ) is a West Germanic language that evolved in the Dutch Cape Colony from the Dutch vernacular of Holland proper (i.e., the Hollandic dialect) used by Dutch, French, and German settlers and their enslaved people. Afrikaans g ...

and Dutch – ''boom'' meaning "tree", and ''slang'' meaning "snake". In

, the name is pronounced . The boomslang is thought to be closely related to members of the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

'' Thelotornis'', '' Thrasops'', '' Rhamnophis'', and '' Xyelodontophis'', with which it forms the taxonomic

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confl ...

Dispholidini.

Subspecies

Two subspecies are recognized, including the

nominotypical subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...

. * ''D. t. kivuensis'' * ''D. t. typus'' The trinomial authority in parentheses for ''D. t. typus'' indicates that the subspecies was originally described in a genus other than ''Dispholidus''.

Description

The average adult boomslang is in total length. Some exceed . The

eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and c ...

are exceptionally large, and the head has a characteristic egg-like shape. Coloration is highly variable. Males are light green with black or blue scale edges, but adult females may be brown. This is known as sexual dimorphism. Weight varies from , with an average weight of . 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 A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

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 subcaudal scales are paired. Ventral scales are 164–201; the anal plate is divided; and the subcaudals are 91–131.

Geographic range

The boomslang is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

to sub-Saharan Africa. It is found in

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

Eswatini Eswatini ( ; ss, eSwatini ), officially the Kingdom of Eswatini and formerly named Swaziland ( ; officially renamed in 2018), is a landlocked country in Southern Africa. It is bordered by Mozambique to its northeast and South Africa to its ...

Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Mala ...

Botswana Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kal ...

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and e ...

and north through sub-Sahara Africa.

Habitat

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. Boomslangs are not restricted to trees and can often be found on the ground to hunt, feed, or take shelter. They will occasionally hide underground when the weather is harsh.

Reproduction

The boomslang is

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), a ...

, 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 Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, the in ...

. Male

hatchling In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird. A group of mammals called monotremes lay eggs, and their young are hatchlings as well. Fish Fish hatchlings generally do not receive parental care, similar ...

s are grey with blue speckles, and female hatchlings are pale brown. They attain their adult coloration after several years. Hatchlings are about 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.

Behavior and diet

''D. typus'' is diurnal and almost exclusively

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose num ...

. It is reclusive, and moves from branch to branch when pursued by anything too large to eat. Its

diet Diet may refer to: Food * Diet (nutrition), the sum of the food consumed by an organism or group * Dieting, the deliberate selection of food to control body weight or nutrient intake ** Diet food, foods that aid in creating a diet for weight loss ...

includes chameleons and other arboreal

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...

frog A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" '' Triadobatrachus'' is ...

s, and occasionally small mammals,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, and eggs from nesting birds, all of which it swallows whole. Boomslangs will also feed on other snakes, including cannibalizing members of their own species. During cool weather, boomslangs

brumate Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be clos ...

for short periods, often curling up inside the enclosed

nest A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...

of a weaverbird.

Venom

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 located in the back of the jaw. The boomslang is able to open its jaws up to 170° when biting. The venom of the boomslang is primarily a

hemotoxin Hemotoxins, haemotoxins or hematotoxins are toxins that destroy red blood cells, disrupt blood clotting, and/or cause organ degeneration and generalized tissue damage. The term ''hemotoxin'' is to some degree a misnomer since toxins that damag ...

; it works by a process in which so many small clots form in the blood that the victim loses the ability to clot further and the victim may die as a result of internal and external bleeding. The venom has been observed to cause hemorrhaging into tissues such as muscle and the brain while at the same time clogging capillaries with tiny blood clots. Other signs and symptoms include

headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a resul ...

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...

, sleepiness, and mental disorders. Because boomslang venom is slow-acting, symptoms may not become apparent until many hours after the bite. Although the absence of symptoms provides sufficient time for procuring

antivenom Antivenom, also known as antivenin, venom antiserum, and antivenom immunoglobulin, is a specific treatment for envenomation. It is composed of antibodies and used to treat certain venomous bites and stings. Antivenoms are recommended only if ...

, it can also provide victims with false reassurance, leading to their underestimating the seriousness of the bite. Snakes of any species may sometimes fail to inject venom when they bite (a so-called "dry bite"), so after a few hours without any noticeable effects, victims of boomslang bites may wrongly believe that their injury is not serious or life-threatening. 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 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is ...

(LD₅₀) in mice is 0.1 mg/kg (intravenously). 0.071 mg/kg (IV) has also been reported. 12.5 mg/kg (

subcutaneously The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and ma ...

) 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, the lethal dosage for a man would be only 2 to 3 mg. In 1957,

herpetologist Herpetology (from Greek ἑρπετόν ''herpetón'', meaning " reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and r ...

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 envenomations by boomslangs between 1919 and 1962, two of which were lethal. Boomslang monovalent 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 transfusion Blood transfusion is the process of transferring blood products into a person's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but m ...

s, 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, it inflates its neck and assumes an "S"-shaped striking pose.

Gallery

File:MaleBoomslang.jpg, A male boomslang File:Boomslang_-_Western_Cape.jpg, Boomslang in Western Cape, South Africa

References

External links

Boomslang (''Dispholidus typus'')

Boomslang vs.Chameleon NatGeo

Boomslang predation on Sabota Lark nest (with video)
{{Taxonbar, from=Q893048 Afrikaans words and phrases Dispholidus Reptiles described in 1828 Snakes of Africa Venomous snakes