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Dispholidus typusBoomslang

By Katlin Coffey and Amanda Robinson

Geographic Range

Dispholidus typus is a terrestrial snake species that is widely distributed throughout Africa. It is indigenous to Africa and not introduced to any other regions. This species is most commonly found in the central and southern regions of the continent. They are most abundant in Swaziland, Botswana, Namibia, Mozambique, and Zimbabwe, but have been observed as far north as Nigeria and southern Chad, and have been reported as far east as eastern Guinea. (Marais, 2004; Toit, 1980)

Habitat

Dispholidus typus is found in a variety of ecosystem types throughout Africa. They are commonly found in karoo scrubs, arid savannas, and east African lowland forests that range in elevation from 1200 to 1400 m. Karoo scrubs are low-lying semi-desert areas unique to South Africa. They have numerous dry seasons throughout the year. The vegetation is composed of a large variety of short, low-lying trees and shrubs. A savanna consists of a variety of grasses with several species of small, single-stemmed trees. The east African lowland forest has more abundant moisture and is composed of a greater diversity and abundance of trees than karoo and savanna. Boomslangs are also found in the Eastern and Central Plateaus (1400 to 3300 m) and in grasslands (1600 to 1700 m). The plateaus are a mountainous region located just off the coastline. These grasslands have plenty of water with thick, diverse vegetation. The most likely place to find this reptile is in the moistest areas within these regions, they tend to avoid extremely dry, desert-like ecosystems. They mainly live in low-lying shrubs and short trees. They have long, slender bodies with various colors that tend to blend with the trees and shrubs within these areas. They will occasionally move to the ground for the primary purpose of hunting and soaking up the sun. (Marais, 2004; Palmer and Ainslie, 2005; Palmer and Ainslie, 2006)

  • Range elevation
    1200 to 1700 m
    3937.01 to 5577.43 ft
  • Average elevation
    1500 m
    4921.26 ft

Physical Description

Boomslangs are long, slender snakes with small, stubby, egg-shaped heads and very large eyes. The average length of an adult is 1.2 to 1.5 meters. Since these snakes are long and slender, they can move through the trees swiftly to catch prey or flee from danger. They exhibit sexual dimorphism because the female and male differ in color. The females are generally a greenish-brown color with a light shade of brown on their bellies. Males, however, are much more colorful and can exhibit a variety of colors. They can be a deep, olive-green or bright green with black outlining of their scales. The males have also been seen with a dark brown or black dorsal scales and a bright yellow or gray belly. Early in the life of boomslangs, they are grey and have bright yellow throats with black specks. It may take a couple of years for young snakes to attain their adult color. Colubrids in general have relatively large scales on their belly. Boomslangs have an average of nineteen rows of very keeled scales. They also typically have nine large scales on their head. (Marais, 2004; Ricciuti, 2001; Toit, 1980)

Dispholidus typus is classified as a member of Solenoglypha because of their ability to fold their fangs back into their mouth when unused. Dispholidus typus is considered one of the most venomous of these rear-fanged snakes. When they bite, it appears as though they are chewing because of their rear-fangs. It is possible for boomslangs to open their mouth one-hundred seventy degrees. They primarily have very potent hemotoxic venom that they inject into their victim, attacking their circulatory system. This venom stops the clotting ability of blood causing the victim to bleed to death both internally and externally. This slow-acting venom causes symptoms to start occurring in the victim several hours after contact and can be fatal if proper treatment is not given. (Marais, 2004; Ricciuti, 2001; Toit, 1980)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range length
    1.2 to 2.0 m
    3.94 to 6.56 ft
  • Average length
    1.5 m
    4.92 ft

Development

Sex of boomslang offspring is temperature dependent. In the spring, boomslangs hatch from their eggs after an incubation time of 2 to 3 months and can quickly grow up to 1 to 1.5 m in length. Females are usually an olive-brown color while the males are usually a vibrant green color with streaks of black and blue on the edges of their scales.

  • Development - Life Cycle
  • temperature sex determination

Reproduction

The mating season for male and female boomslangs has been observed in December and January. Females follow hormonal trail left behind by the male. Unlike most other snakes, boomslangs can mate in trees. They also can mate on the ground. They do not mate for life, but there is little information on how many mates a boomslang will have in its lifetime. (Boycott and Morgan, 1990; Marais, 2004)

Female boomslangs follow the scent of male hormone trails. After mating, there is a period from four to eight weeks before the female lays eggs. Eggs are usually laid in an area of decay, such as a rotting tree stump or pile of leaves. On average, eight to fourteen leathery eggs are laid and up to 27 have been observed. After the eggs have been laid, the female generally leaves the eggs alone and never returns to check on the young. The snakes hatch using a special "egg tooth" to work their way out of the shell. At birth, the length of the baby snake ranges from 29 to 38 cm. As hatchlings, boomslangs need to eat every two or three days. At this stage, their diet consists mainly of smaller reptiles. Their first skin shedding occurs when they are approximately ten days old. (Boycott and Morgan, 1990; Marais, 2004)

  • Breeding interval
    Boomslangs breed once yearly.
  • Breeding season
    Eggs are laid from late spring to early summer.
  • Range number of offspring
    8 to 27
  • Average number of offspring
    14
  • Range gestation period
    4 to 8 weeks
  • Average time to independence
    10 days
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

Generally, females lays the eggs in a nest of rotting vegetation to aid in incubation. Once the young hatch, they are independent.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

There is little known about the lifespan and longevity of boomslangs. In the wild, they avoid interaction with humans, making it difficult to observe them in their natural environment. Based on observation in captivity, it is estimated that boomslangs live approximately eight years in the wild. Their lifespan in captivity is slightly longer and the main reason for this is the absence of predation. (Boycott and Morgan, 1990; Marais, 2004)

  • Average lifespan
    Status: captivity
    8.7 years
  • Average lifespan
    Status: wild
    8 years

Behavior

Boomslangs are solitary reptiles that rarely communicate with, and will even prey upon, other members of their species. Boomslangs spend most of their day hunting in trees and shrubs, carefully gliding through tree branches until an ideal hiding place is found. Boomslangs strike without warning and are able to capture most of their prey without being seen. These diurnal, arboreal snakes spend most of the day camouflaged in tree branches waiting for prey and spend most of their time curled up in warm bird nests during the colder months while often hibernating for periods of time. Since boomslangs live in warmer climates and hibernate during cooler weather, there is no need for migration. (Marais, 2004; Pope, 1958)

Home Range

Boomslangs spend most of their time off of the ground, in trees, and are primarily found in densely wooded grasslands with plenty of hiding places nearby. They do not tend to stray far from their tree. Territory size for boomslangs is unknown. (Stuart and Stuart, 2009)

Communication and Perception

Little is known about the communication and perception abilities of boomslangs. Snakes, in general, do not have well developed eyesight but are able to see movement and color. Boomslangs, however, have stereoscopic vision allowing them to have good depth perception and color vision. Because they do not have a well-developed sense of smell, they rely on sensing vibrations on the ground and flicking their tongues outside of their mouths as a means of detecting chemical scents in the air. Colubrids in general secrete a foul-smelling odor when threatened and use pheromones in attracting mates. Boomslangs are generally solitary. As a result, they rarely communicate with other animals unless they feel threatened. When threatened, they have the ability to make their bodies appear larger by widening their neck and opening their mouth. Boomslangs rarely strike except, as a means of catching prey or if they are handled in captivity. When striking does occur, however, they do not give a warning sign before attacking. (Stuart and Stuart, 2009; Young, 2003)

Food Habits

Boomslangs are carnivorous. Their main diet consists of small arboreal lizards and frogs, including chameleons. Occasionally, they feed on small mammals, birds, the eggs of reptiles and birds, and even cannibalize other boomslangs. Most colubrids do not change their diet throughout their lives. After injecting their prey with their highly potent, haemotoxic venom, they swallow their prey whole. Boomslangs, like most other snakes, can consume large prey because of their ability to unhinge their jaws and use muscles throughout their body to move their food down their digestive tract. (Marais, 2004)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
    • eats eggs
  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs

Predation

Boomslangs are preyed upon by some of the larger carnivorous birds indigenous to southern Africa, as well as by their own species. Boomslangs spend most of their time in low-lying shrubs and short trees where their long, slender bodies and varied coloration provide excellent camouflage, hiding them from predators and aiding in the capture of prey. The coloring of boomslangs helps to camouflage them in their arboreal habitats, even at a young age. It is not know whether or not boomslangs are more prone to being preyed upon at certain stages of their lives. (Marais, 2004; Stuart and Stuart, 2009; Young, 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

There is little documentation on the importance of boomslangs to their environment. They are, however, important as prey for various birds, including falcons and kestrels (Falconidae) and eagles and vultures (Accipitridae). (Marais, 2004; Stuart and Stuart, 2009; Young, 2003)

Economic Importance for Humans: Positive

There are no documented positive effects of boomslangs on humans. Boomslang venom may be useful in research of the effects and treatment of haemotoxic venom.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

The highly potent venom of boomslangs can cause death in humans, but they typically only strike if handled.

  • Negative Impacts
  • injures humans

Conservation Status

Boomslangs are at no risk of becoming endangered or threatened at the present time. ()

Contributors

Katlin Coffey (author), Radford University, Amanda Robinson (author), Radford University, Christine Small (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Akani, G., N. Ebere, L. Luiselli, E. Eniang. 2007. Community structure and ecology of snakes in fields of oil palm trees (Elaeis guineensis) in the Niger Delta, southern Nigeria. African Journal of Ecology, 46: 500-506.

Boycott, R., D. Morgan. 1990. Observations on reproduction in southern African Boomslang. Journal of the Herpetological Association of Africa, 38/1: 51-52.

Braack, H. 1981. Lower vertebrates of the Bontebok National Park. Koedoe, 24: 67-77.

Gomperts, E., D. Demetriou. 1977. Laboratory studies and clinical features in a case of Boomslang envenomation. South African Medical journal, 51: 173-176.

Graham, J., J. Blair. 1954. The pigments of snake skins. Biochemical Journal, 56/2: 286-287.

Honegger, R. 2007. Notes on some amphibians and reptiles at Zurich Zoo. International Zoo Yearbook, 9/1: 24-28.

Kochva, E., M. Wollberg. 1970. The salivary glands of Aparallactinae (Colubridae) and the venom glands of Elaps (Elapidae) in relation to the taxonomic status of this genus. Zoological Journal of the Linnean Society, 49/3: 217-224.

Marais, J. 2004. Complete Guide to Snakes of Southern Africa. Cape Town: Struik Publishers.

McAllister, C., C. Bursey, P. Freed. 2010. Nematode parasites of some reptiles (Sauria: Testudines: Ophidia) from the northern and western cape provinces, South Africa. Journal of Parasitology, 96/5: 1021-1026.

Mebs, D. 2002. Venomous and Poisonous Animals: A Handbook for Biologists, Toxicologists and Toxinologists, Physicians and Pharmacists. Boca Raton, FL: GmbH Scientific Publishers.

Menez, A. 2003. The Subtle Beast: Snakes, From Myth to Medicine (Science Spectra). New York, NY: Taylor & Francis.

Nicolson, I., P. Ashby, N. Johnson, J. Versey, L. Slater. 1974. Boomslang bite with haemorrhage and activation of complement by the alternate pathway. Clinical and Experimental Immunology, 16/2: 295-300.

Palmer, A., A. Ainslie. 2005. Grasslands of South America. Pp. 77-116 in J Suttie, S Reynolds, C Batello, eds. Grasslands of the World. Rome, Italy: Publishing Management Service. Accessed October 22, 2011 at ftp://ftp.fao.org/docrep/fao/008/y8344e/y8344e00.pdf.

Palmer, A., A. Ainslie. 2006. "South Africa" (On-line). Accessed October 22, 2011 at http://www.fao.org/ag/AGP/AGPC/doc/Counprof/southafrica/SouthAfrica.htm.

Pope, C. 1958. Fatal bite of captive African rear-fanged snake (Dispholidus). Copeia, 4: 280-282.

Ricciuti, E. 2001. The Snake Almanac. New York: The Lyons Press.

Spottiswoode, C. 2009. Fine-scale life-history variation in sociable weavers in relation to colony size. Journal of Animal Ecology, 78: 504-512.

Stuart, C., M. Stuart. 2009. Dangerous Creatures of Africa. Cape Town 8000, South Africa: Struik Nature.

Toit, D. 1980. Boomslang Bite: A case report and a review of diagnosis and management. South African Medical journal, 57: 507-510.

Young, B. 2003. Snake bioacoustics: toward a richer understanding of the behavioral ecology of snakes. Quarterly Review of Biology, 78/3: 302-325.

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