Brown Tree Snake

Boiga irregularis

Last updated: April 6, 2023
Verified by: AZ Animals Staff
© Janelle Lugge/

People have reported seeing these snakes in Texas, Oklahoma, and Hawaii, but this has never been proven!


Brown Tree Snake Scientific Classification

Scientific Name
Boiga irregularis

Read our Complete Guide to Classification of Animals.

Brown Tree Snake Conservation Status

Brown Tree Snake Locations

Brown Tree Snake Locations

Brown Tree Snake Facts

Birds, rates, bats, lizards, and small mammals
Name Of Young
Group Behavior
  • Solitary
Fun Fact
People have reported seeing these snakes in Texas, Oklahoma, and Hawaii, but this has never been proven!
Most Distinctive Feature
Slender body and tail
Other Name(s)
Brown cat snakes, culepla
Incubation Period
90 days
Tropical and subtropical environments
Average Litter Size
4-2 eggs
  • Nocturnal
Common Name
Brown tree snake
Australia, Papua New Guinea, Indonesia

Brown Tree Snake Physical Characteristics

  • Brown
  • Green
Skin Type
10-15 years
5 lbs
4-8 ft
Age of Sexual Maturity
3-4 years

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View all of the Brown Tree Snake images!

The brown tree snake has a reputation as one of the most aggressive invasive species.

The brown tree snake, often referred to as the brown cat snake, can be found in Australia, Indonesia, and Papua New Guinea. You can identify these snakes by their vertical cat-like pupils, hence the nickname. In addition, they have large heads and slender bodies and are active nocturnal predators.

The brown tree snake is an invasive species because of their adverse effects on indigenous fauna, which may cause the extinction of many native species. Researchers observed this behavior when these snakes were originally introduced to Guam in the 1940s.

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Because these snakes reproduce throughout the year, their population numbers are experiencing sustainable growth. In addition, the brown tree snake is not a significant threat to humans because they are only mildly venomous.

4 Amazing Facts About Brown Tree Snakes!

  • These snakes are known for their bad tempers and will repeatedly strike if cornered or threatened.
  • The brown tree snake’s fangs are located in the back of their mouths, making biting humans and injecting venom difficult unless the snake is very large in size.
  • These snakes come in a variety of colors, including brown, green, red, yellow, and cream.
  • Their limited diet consists of small mammals and birds, but juveniles like to prey on small lizards.
A Brown Tree Snake Coiled on Branch
The brown tree snake is found in a variety of colors.

©Tailored Photography/

Scientific Name

The brown tree snake’s scientific name is Boiga irregularis, and they belong to the order Squamata, which means “scaly or having scales.” Squamata is the largest order in the class Reptilia and members include lizards and amphisbaenians, also called worm lizards.

Evolution and Origins

Brown tree snakes are members of the family Colubridae, which contains some of the most common snake species. You can identify them by the complete absence of hind limbs and their lack of teeth on the premaxilla. In addition, most species in this family have very few head scales, a loose facial structure, and ventral scales as broad as their bodies.

This snake has evolved its climbing technique to adapt to its environment in Guam, where it is an invasive species. Scientists were surprised to discover in 2017 that the brown tree snake moves in a way like no other snake before has been observed doing. The snake was seen climbing a vertical pipe by wrapping its tail around it and grabbing the other end of its body to make a loop and shimmy upward in what scientists have named “lasso locomotion.” This discovery revealed how the brown tree snake has managed to devastate the populations of 10 species of Micronesian birds and provided insights into how to protect the remaining Micronesian starlings.

A brown tree snake on a tree trunk
The brown tree snake has evolved to be able to move in a “lasso locomotion” vertically.

©Janelle Lugge/

Types of Tree Snakes

The brown tree snake is one of several types of tree snakes. These include:

Australian Tree Snake (Dendrelaphis punctulatus)

The Australian tree snake is often referred to as the green tree snake. These diurnal snakes have large eyes and slender bodies and are non-venomous. They are native to many regions in Australia, specifically along the northern and eastern coastlines, up to Papua New Guinea. The Australian tree snake’s most distinguishing feature is its slender body and tail, which make this snake incredibly agile.

The top of their slender bodies varies in color from golden yellow, olive green, bright green, black, and sometimes blue. However, their bellies and throats are usually pale yellows with blue flecks on their flanks. Their large eyes generally have golden irises with large, round pupils. Australian tree snakes occur in rainforests, woodlands, and urban areas, and they prey on smaller animals like frogs and fish.

These snakes do not constrict their prey, nor are they venomous. Instead, they rely on their sharp set of teeth to chew the prey and plunge it down their esophagus.

The Australian tree snake has a slender body and tail.

©Pete Niesen/

Blunt-Headed Tree Snake (Imantodes cenchoa)

The blunt-headed tree snake occupies the forests of South America. These snakes have incredibly broad heads when compared to other tree snakes, and their eyes are large with cat-like vertical pupils.

Blunthead Tree Snake, Napo River Basin, Amazonia, Ecuador
The blunt-headed tree snake has similar eyes to the brown tree snake.

© Carrera

Paradise Tree Snake (Chrysopelea paradise)

Paradise tree snakes are often referred to as the paradise flying snake, and they are native to southeastern Asia. They belong to the Genus Chrysopelea, which consists of snakes that can glide from the tops of trees by stretching their bodies into flattened ribbon-like strips using their ribs.

They primarily occur in moist forests and can travel distances of 32 feet while gliding from the tops of trees. While performing this amazing skill, their bodies remain relatively stable, suggesting some form of controlled flight.

Paradise tree snakes are mildly venomous, but because of their rear fangs, they are not considered dangerous to humans. Instead of using venom, they constrict their prey and like to feed on lizards and bats.

A paradise flying snake stretches off a tree branch
Paradise flying snakes can glide between treetops.

©Vince Adam/


Brown tree snakes are slender and agile. Their fangs sit in the back of their mouths; opisthoglyphous is the name of this strange characteristic. But other distinguishing features of their vertical, cat-like pupils, their heads are larger than their bodies, and these snakes come in a wide variety of colors, the most common including:

  • Brown
  • Green
  • Brown with crossbands.

However, they also come in red, yellow, or cream colors.

This snake can grow up to 4-8 feet long. However, some of the brown tree snakes located on Guam measured as long as 10 feet, similar to the Lancehead snake’s length. In addition, these snakes weigh up to 5 pounds by the time they are fully grown.

Brown tree snake head shot accentuates eyes
Brown tree snakes have large eyes that resemble a cat’s.

©Matt Cornish/


Not much is known about the brown tree snakes’ behavior. For example, researchers are still unsure whether they live a solitary life or in groups. However, they have managed to figure out that the brown tree snake males live on their own for most of their lives. In addition, they hibernate in abandoned animal burrows during the winter months.

Venom: How Dangerous Are Brown Tree Snakes?

The brown tree snake has quite a reputation as one of the most aggressive invasive species. However, their bite is not dangerous to adults but can cause a reaction in children. Typically, the brown tree snake reacts by striking its target repeatedly when under threat or cornered.

These aggressive snakes are only mildly venomous, and there are no recorded deaths resulting from their bite. However, children have had reactions to their venom, but none were fatal.

Head shot of a brown tree snake flicking its tongue
Brown tree snakes are aggressive but only mildly venomous.



Brown tree snakes are native to Australia, Papua New Guinea, and the Solomon Islands. However, in the 1950s, scientists discovered them on the island of Guam. In addition, people reported seeing them in Texas, Oklahoma, and Hawaii, but this has never been proven.

These snakes are highly adaptable, and their habitats vary significantly over a wide range of tropical and subtropical environments on several islands.

In Guam, they are an invasive species as their presence is causing a severe ecological impact on the native lizard and bird species on the island, who act as pollinators. Because of this, there has been a significant decline in native plant species in Guam.

The brown tree snake is an invasive species in Guam.



These snakes like to prey on smaller animals, including:

ground skink
Skinks are part of the brown tree snake’s diet.

©Ryan M. Bolton/

Predators and Threats

Natural predators of brown tree snakes are wild pigs, birds of prey, large lizards including mangrove monitors, and other snake species such as red-bellied black snakes. However, in Guam, where this snake is an invasive species, there are few predators so its population has rapidly expanded.

Smallest Animals: Wild Pigs
Feral hogs are one of the brown tree snake’s natural predators.


Reproduction, Babies, and Lifespan

These snakes keep their population numbers consistent because they reproduce all year round. In addition, female brown tree snakes can lay 3 to 12 clutches per year! These snakes lay their eggs in hollow logs, caves, or rock crevices, and the clutches appear leathery in texture.

The snakelets hatch after 90 days of incubating, and the offspring measure around 19 inches long. In addition, these snakelets take three to four years to reach sexual maturity. The brown tree snake has no paternal instincts, and once females have laid their eggs, they leave them to fend for themselves.

These snakes have a relatively long lifespan of 10-15 years in the wild.

Brown tree snake displaying pattern
Brown tree snakes reproduce year-round.

©Mike Veitch/

Population and Conservation

Brown tree snakes are a common species, and their population numbers are stable. The IUCN Red List classifies them as Least Concern, but the exact number of their population is unknown.

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About the Author

I am a 33-year-old creative and professional writer from South Africa. Wildlife is one of my greatest passions and led me to become the writer I am today. I was very blessed to work with an abundance of wildlife (mainly big cats) and captured my unique experiences in writing. But I wanted to take it further, and I ventured into the freelancing world. Now, I get to spend my days writing about animals; what could be better?

Brown Tree Snake FAQs (Frequently Asked Questions) 

Are brown tree snakes in the United States?

There have been reported sightings in Texas, Oklahoma, and Hawaii, but this has never been proven.

What is another name for the brown tree snake?

Brown tree snakes are also called brown cat snakes or culepla.

Are brown tree snakes aggressive?

The brown tree snake has quite a reputation as one of the most aggressive invasive species. However, their bite is not dangerous to adults but can cause a reaction in children.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.

  1. Wikipedia, Available here:
  2. Invasive Species Info, Available here:
  3. Kidadl, Available here:,they%20are%20nocturnal%2C%20active%20predators.
  4. IUCN Redlist, Available here:

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