Brown Tree Snake Fact File

Boiga irregularis








Wild 13 years

Captive 13 years



Frog, Birds, Mammals

Conservation Status


Least Concern

The Brown tree snake is a rear-fanged snake found naturally across Australia, New Guinea, Indonesia and a range of smaller islands.

Unfortunately they are best known following their introduction to the island of Guam where they have contributed to the extinction of a number of native birds and lizards.

They hunt for a range of small vertebrates including birds and their eggs, lizards and frogs. A single brown tree snake may consume up to 70% of its body weight each day.

Juveniles are colored yellow and take on the adult coloration as they grow. They are responsible for themselves from birth with no parental care provided.

Learn more about these snakes by reading on below.


Brown tree snakes have incredibly slender bodies cover with scales which are marked with a pattern of dark brown or blackish bands which cover the greyish or reddish brown background. On the underside they are colored whitish to salmon.

Their head is broad and distinguished from the neck. These snakes have a large orange eye with a distinct black vertical pupil which appears to bulge out of the head.

They reach a length of up to 2m (6.6ft) long with a weight of 525g (18.5oz).


Brown tree snakes are carnivores. They feed on a range of birds, small mammals and reptiles such as lizards. This will include dragon lizards which they primarily capture while they sleep on branches at night.

On Guam they primarily consume lizards and skinks which reproduce quickly and can help to sustain the population at its high levels.

Carrion (dead prey) may also be consumed allowing them to exploit all available food sources.

They will grasp their prey in the coils of the forebody to help subdue it.

These predators are voracious and can feed on up to 70% of their body mass each day.

Brown Tree Snake


Brown tree snakes live in the Australasian region. Here they can be found in the following countries - Australia; Indonesia; Papua New Guinea and the Solomon Islands. They also live on a number of islands within the Torres Strait.

The species was introduced to Guam soon after the second world war. It is thought they arrived hidden in cargo. They have also spread to Cocos Island, a small atoll off the shore of Guam.

At least eight individuals have arrived on Hawaii from Guam with deliveries but the species has not established here.

In Australia they live along the northern coastline through Western Australia, Queensland, New South Wales and the Northern Territory.


These snakes make their home in sclerophyll forest, rock outcrops, eucalypt woodland, rainforest, mangroves and woodland.

They shown an ability to live alongside humans in plantations, rural areas and even some urban centers.

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A female brown tree snake produces between 2 and 11 eggs from which their young hatch. Each year they may produce up to two clutches. The eggs are deposited in a hollow log or rock crevice.

Female brown tree snakes have the ability to store sperm from a mating for several years which means they can breed years after the last encounter with a male.

The mother provides no care to their young while in the egg or after they hatch. The eggs incubate for 90 days and once they hatch they must feed for and defend themselves.

Hatchlings are colored yellow and begin to take on the adult coloration as they grow.

It has been noted that this species may have the ability to reproduce asexually (without mating).


Brown tree snakes are primarily nocturnal but during winter they may emerge to bask in the sun.

These animals are rear fanged and venomous but until recently they have not been considered dangerous to humans. Recent cases in Guam have seen trouble breathing in children which were bitten.

To inject their venom they will grasp the prey and repeatedly chew it to inject the venom. If bitten by a snake one should always seek medical attention.

Most of their time is spent in the trees making this species arboreal. They can also scale rock faces and buildings in human inhabited areas. Some may seek shelter in tree hollows or sandstone caves.

Brown Tree Snake

Predators and Threats

Recorded natural predators of the brown tree snake include monitor lizards and larger sakes.

Introduced predators such as feral dogs, pigs, cane toads and cats may harm brown tree snakes.

When threatened the brown tree snake will raise up its forebody in a series of tight loops. They are considered aggressive and strike at a threat with little notice.

Their range has been expanded through introduction to Guam. Here they have caused devastation to the birds and bats which call the island home. They also cause damage to power infrastructure by crawling over the lines. Significant efforts are being invested in eradicating this population.

These animals are considered common with their population believed to be stable.

Brown tree snakes are present in the pet trade. Humans may affect them through fire and habitat loss.

Quick facts

These animals may also be know as the brown catsnake, culepla, banded tree snake, night tiger or Doll's eye.

Brown tree snakes are part of the world's largest snake family, the colubrids. This group includes 2000 species.

Brown Tree Snake

Photo Credits

Top and Bottom

Public Domain

Middle One

Pavel Kirillov from St.Petersburg, Russia, CC BY-SA 2.0 <>, via Wikimedia Commons

Middle Two

John attkinson, CC BY-SA 4.0 <>, via Wikimedia Commons


Swanson, S. and Parish, S., 2011. Field Guide To Australian Reptiles. 2nd ed. New South Wales: Pascal Press.

Allison, A., Tallowin, O., O'Shea, M., Parker, F., Greenlees, M. & Wilson, S. 2018. Boiga irregularis. The IUCN Red List of Threatened Species 2018: e.T196562A2460107. Downloaded on 19 June 2021. 2021. Brown Tree Snake - Queensland Museum. [online] Available at: <> [Accessed 19 June 2021]. 2021. Brown Tree Snake. [online] Available at: <> [Accessed 19 June 2021]. 2021. What is the brown treesnake?. [online] Available at: <> [Accessed 19 June 2021].

Territory Wildlife Park. 2021. Brown Tree Snake. [online] Available at: <> [Accessed 19 June 2021].

Park, A., 2021. Brown Tree Snake - Australian Reptile Park. [online] Australian Reptile Park. Available at: <> [Accessed 19 June 2021].

Encyclopedia Britannica. 2021. brown tree snake | Habitat, Control Methods, & Facts. [online] Available at: <> [Accessed 19 June 2021].

Hawaii Invasive Species Council. 2021. Brown Tree Snake. [online] Available at: <> [Accessed 19 June 2021]. 2021. Brown tree snake (Boiga irregularis) longevity, ageing, and life history. [online] Available at: <> [Accessed 19 June 2021].

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