The Brown Tree

Snake

The brown tree snake was accidentally introduced to

Guam in the late 1940s or early 1950s, probably from

the Solomon Islands. A native of Australia, Papua

New Guinea, and the Solomon Islands, the brown

tree snake (Boiga irregularis) is a dangerous threat to

the economy and ecology of Guam and is the subject

of a cooperative program to control snake populations on Guam and prevent its spread throughout the

Pacific Rim.

Biology

Brown tree snakes are about 15 inches at hatching and may reach 10 feet in length as adults. Most

brown tree snakes are 3 to 4 feet long. This snake is

a rear-fanged semiconstrictor and is mildly poisonous. Both constriction and venom are used to help

immobilize prey.

The snake’s venom trickles into a bite victim

along grooves in the rear fangs. Because of the relatively small size and position of the fangs, a brown

tree snake must chew to allow the fangs to penetrate

the skin.

The brown tree snake will readily strike when

aggravated, but it does not present a danger to

adults. A bite from this snake will not penetrate most

clothing. However, babies less than 6 months old

may be at risk from both brown tree snake bites and

constriction. A young victim of a brown tree snake

bite should receive immediate medical attention.

The snake is active at night and inhabits trees,

shrubs, and forests. Although snakes are usually

found in vegetation, they can be encountered almost

anywhere. The brown tree snake spends most days

coiled in a cool and dark location, such as a treetop

or a rotted log. They are adept climbers and can

crawl through very small openings.

The brown tree snake is extremely abundant on

Guam, with localized estimates sometimes reaching

20 or more snakes per acre of jungle. These population density estimates are among the highest snake

densities ever recorded. The only other snake on

Guam, the introduced blind snake (Ramphotyphlops

braminus), resembles a worm in size and shape and

is harmless.

Damage

The brown tree snake has caused extensive economic and ecological damage to Guam. It is responsible for numerous power outages across the island

each year. This species is an opportunistic feeder

and has eradicated most of Guam’s native forest

birds.

As bird populations have declined, the snake has

turned its focus to Guam’s lizards. Rats, mice,

domestic birds, and bird eggs make up the rest of the

snake’s diet on Guam. In the snake’s native range,

its populations are kept in check through natural

processes such as disease, competition for food, and

predation. Although these processes likely occur on

Guam, they are not adequate enough to control the

brown treesnake population.

Conflicts With People

Even though the snake is abundant on Guam,

most people rarely encounter a live brown tree

snake. These pests do not hang from trees in giant

bunches, nor do they actively search out people to

bite. In fact, many residents have lived on Guam for

years without ever seeing a single snake.

The brown tree snake may be attracted to residential areas by an abundance of rodents, lizards,

poultry, or debris that serves as habitat for snake

prey. The snake may occasionally enter buildings

while searching for food.

Simple precautions, such as keeping doors and

screens secured, screening air ducts and pipes that

open outdoors, keeping garbage and pet food in

secured containers, and removing surrounding vegetation may make a building less attractive to brown

tree snakes.

If you encounter a brown tree snake indoors, you

should call local authorities for removal.

Factsheet

Wildlife Services November 2001

APHIS
Preventing Its Spread

Without control, the problems caused by the

brown tree snake could spread. The snake has been

sighted on many other Pacific islands. It is believed to

have arrived through cargo transported by ships or

planes originating in Guam. Although no established

snake populations are suspected at these locations,

the possibility of an incipient population on Saipan

exists. These sightings clearly demonstrate the possibility of snakes being transported to vulnerable locations.

The Federal Government’s Wildlife Services (WS)

program, administered by the U.S. Department of

Agriculture’s Animal and Plant Health Inspection

Service (APHIS), coordinates operational efforts on

Guam aimed at keeping the snake from reaching

other destinations. APHIS’ WS personnel use snake

trapping in high-risk areas, trained snake-detector

dogs in cargo, nighttime spotlight searches, and public

education as tools to achieve this goal.

When departing Guam, you can help ensure the

snake does not leave with you by carefully inspecting

your belongings, particularly outdoor goods, when

packing.

For more information about the brown tree snake,

contact the Guam WS office at (671) 635-4400 or the

Hawaii WS State office at (808) 861-8576. You can

also visit the WS Web site at

http://www.aphis.usda.gov/ws.

The U.S. Department of Agriculture (USDA) prohibits discrimination

in all its programs and activities on the basis of race, color, national

origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to

all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at

To file a complaint of discrimination, write USDA, Director, Office of

Civil Rights, Room 326–W, Whitten Building, 1400 Independence

Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964

(voice and TDD). USDA is an equal opportunity provider and

employer.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture