Boiga irregularisBrown catsnake, Brown Tree Snake

Geographic Range

Boiga irregularis, brown tree snakes, are native to northern Australia (New South Wales, Northern Territory, and Queensland), Papua New Guinea, and eastern Indonesia. They have also been accidentally introduced to the Pacific island of Guam (Savidge et al., 2007). (Amand, 2000; Savidge, et al., 2007)


The Brown Tree Snake prefers the lowland woodlands and coastal forests of Northern Australia as well as the more tropical rainforests of Papua New Guinea and Indonesia. However, they are not restricted to forests and have been observed to live in caves and human made structures (i.e. attics, upper portions of buildings, etc.) as well. This snake is often nocturnal and generally takes shelter in hollow logs, tree crowns, caves, or miscellaneous crevices during the day. (Amand, 2000; O'Shea and Halliday, 2001)

Physical Description

The Brown Tree Snake has a very slender and agile body coinciding with its arboreal lifestyle. They generally are a light brown with either darker dorsal markings or a uniform coloration, however, these snakes have also been observed to be red, yellow, pink, or a creamy white. It has a distinctively large head with opisthoglyphous (rearward) fangs and big bulbous eyes characteristic of the genus Boiga (and in keeping with nocturnal habits). They are long, laterally compressed snakes (2 to 2.5 m long) with large vertebral scales and a long tail. Mature Brown Tree Snakes have variable masses ranging anywhere from 60 to 2300 g. (O'Shea and Halliday, 2001; Savidge, et al., 2007)

  • Sexual Dimorphism
  • male larger
  • Range mass
    60 to 2300 g
    2.11 to 81.06 oz
  • Average mass
    523 g
    18.43 oz
  • Range length
    1.03 to 2.91 m
    3.38 to 9.55 ft
  • Average length
    1.7 m
    5.58 ft


As with all squamates, fertilization is internal. Shelled amniotic eggs are laid; the hatchling snakes are essentially miniatures of the adults and grow incrementally. Sex is probably determined genetically, as appears true for all snakes. It is unknown whether Brown Tree Snakes have indeterminate growth. (O'Shea and Halliday, 2001)


These snakes appear to reproduce year-round, but more research is needed on Brown Tree Snake mating systems. (Mathies, et al., 2010; Savidge, et al., 2007)

Male Brown Tree Snakes have been observed to store sperm year-round suggesting aseasonal spermatogensis; however, this is under debate due to the fact that the majority of tropical snakes have seasonal spermatogensis (Mathies et al., 2010). Females have been observed to lay clutches of 3-12 leathery-shelled eggs biannually. Generally, females lay their eggs in hollow logs, rock crevices, or caves in order to protect them from desiccation (Fritts & Rodda, 1998). Eggs hatch after approximately 90 days and offspring are around 50 cm long and take around 3 or 4 years to reach sexual maturity (Savidge et al., 2007). (Fritts and Rodda, 1998; Mathies, et al., 2010; Savidge, et al., 2007)

  • Breeding interval
    Females lay 2 clutches per year
  • Breeding season
    Aseasonal breeding
  • Range number of offspring
    3 to 12
  • Average number of offspring
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 4 years

Brown Tree Snakes abandon their eggs after laying and there is no parental care of the young. (O'Shea and Halliday, 2001; Savidge, et al., 2007)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female


Brown Tree Snakes are reported to have a lifespan ranging from 10-15 years (Amand, 2000). (Amand, 2000)

  • Range lifespan
    Status: wild
    10 to 15 years
  • Range lifespan
    Status: captivity
    9.25 (high) years


Brown Tree Snakes are largely arboreal but have been observed living in non-arboreal situations. They are nocturnal, spending the daytime sheltered in trees, caves, or cliffs and the nighttime hunting and foraging (Campbell et al., 2008). They are also known to be very aggresive towards any potential predator that comes within close proximity (O'Shea & Halliday, 2001). (Campbell, et al., 2008; O'Shea and Halliday, 2001)

Communication and Perception

These snakes undoubtedly have fairly good eyesight, but will predictably depend on detecting chemical cues (odors) via the vomero-nasal ("Jacobson's") organ as in other snakes. Perception of sound has not been studied in this species. More research is needed specifically on Brown Tree Snake communication and perception. (O'Shea and Halliday, 2001)

Food Habits

The Brown Tree Snake eats a wide variety of prey ranging from birds, small mammals, amphibians,and other reptiles. This snake subdues its prey either through the use of its venom or through constricting its prey with its long body (Amand, 2000). In Guam, the Brown Tree Snake is invasive and is believed to have caused the extinction of several bird species, and has greatly reduced populations of other vertebrates (O'Shea & Halliday, 2001). (Amand, 2000; Fritts and Rodda, 1998; O'Shea and Halliday, 2001)

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


In their natural range, Brown Tree Snakes are eaten by wild pigs, birds of prey, and certain other snakes and large lizards, such as monitors. There are few known predators of this snake on the island of Guam, which has allowed the species there to attain abnormally large population density and to grow to larger than average size (Up to 3 m; O'Shea & Halliday, 2001). Brown Tree Snakes are rear-fanged and venomous, and are cryptically colored to hide in vegetation. (Amand, 2000; Fritts and Rodda, 1998; O'Shea and Halliday, 2001)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators

Ecosystem Roles

The Brown Tree Snake is a predator that has normal constraints on its populations in its natural range. It has no natural predators on the island of Guam and therefore has become an apex predator. Because of this, Brown Tree Snakes have become overabundant there and have severely disrupted the ecosystem primarily through its predatory impacts on native vertebrate species (Amand, 2000) (Fritts & Rodda, 1998). (Amand, 2000; Campbell, et al., 2008; Fritts and Rodda, 1998; O'Shea and Halliday, 2001)

Economic Importance for Humans: Positive

The Brown Tree Snake provides no specific benefit towards humans, though in its natural habitat it contributes to a functioning ecosystem. (Fritts and Rodda, 1998; Savidge, et al., 2007)

Economic Importance for Humans: Negative

Brown Tree Snakes are mildly venomous to humans; bites can be painful and occasionally debilitating. Bites to children or infants can be more serious. Where introduced, as on Guam, in addition to ecological damage, this snake can cause power outages by hiding in transformers, and detracts from tourism. Significant economic investments have been made in Guam to eradicate this invasive species from the island. (Amand, 2000; Fritts and Rodda, 1998; O'Shea and Halliday, 2001; Savidge, et al., 2007)

  • Negative Impacts
  • injures humans
  • household pest

Conservation Status

Brown tree snakes are not considered threatened or endangered. Where they have been introduced, they pose a substantial threat to native faunas and eradication programs are active.


Stephen Kerr (author), Michigan State University, James Harding (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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


an animal that mainly eats meat


uses smells or other chemicals to communicate


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.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


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.


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


having the capacity to move from one place to another.

native range

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


active during the night


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


chemicals released into air or water that are detected by and responded to by other animals of the same species


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.


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


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


Living on the ground.


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


living in cities and large towns, landscapes dominated by human structures and activity.


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


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


uses sight to communicate

year-round breeding

breeding takes place throughout the year


Amand, A. 2000. Boiga irregularis (Brown Tree Snakes) on Guam and Its Effect on Fauna. Restoration and Reclamation Review, 6/6: 1-6.

Campbell, S., S. Mackessy, J. Clarke. 2008. Microhabitat Use by Brown Treesnakes (Boiga irregularis) Effects of Moonlight and Prey. Journal of Herpetology, 42/2: 246-250.

Fritts, T., G. Rodda. 1998. THE ROLE OF INTRODUCED SPECIES IN THE DEGRADATION OF ISLAND ECOSYSTEMS: A Case History of Guam. Annu. Rev. Ecol. Syst., 29: 113-140.

Mathies, T., J. Cruz, V. Lance, J. Savidge. 2010. Reproductive Biology of Male Brown Tree Snakes (Boiga irregularis) on Guam. Journal of Herpetology, 44/2: 209-221.

O'Shea, M., T. Halliday. 2001. Reptiles and Amphibians. United States: Dorling Kindersley.

Savidge, J., F. Qualls, G. Rodda. 2007. Reproductive Biology of the Brown Tree Snake, Boiga irregularis (Reptilia: Colubridae), during Colonization of Guam and Comparison with That in Their Native Range. Pacific Science, 61/2: 191-199.