The brown tree snake (Boiga irregularis) was accidentally introduced to 

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

Islands. Native to northeastern Australia, eastern Indonesia, and Melanesia, 

the brown tree snake has signifi cantly damaged the economy and ecology 

of Guam. WS’ cooperative program seeks to control snake populations on 

Guam and prevent its spread throughout the Pacifi c Rim. 

Biology 

About 15 inches in length at hatching, brown tree snakes may reach 10 feet 

in length as adults; however, most snakes on Guam are 3 to 4 feet long. The 

brown tree snake is rear-fanged and considered mildly venomous. It uses 

both constriction and venom to help immobilize its prey. 

Brown tree snake bites will not penetrate most clothing. Because of the 

fangs’ position and relatively small size, a brown tree snake must chew to 

allow its fangs to penetrate skin. Venom enters bite victims along grooves in 

the snake’s rear fangs. 

Although the brown tree snake will readily strike when aggravated, it 

does not present a danger to adults. Infants less than 6 months old may 

however be at risk from both bites and constriction; young bite victims 

should receive immediate medical attention. 

The brown tree snake is an adept climber and inhabits trees, shrubs, 

and forests. They spend most days coiled in cool dark locations, such as 

treetops or in rotted logs. At night, they become active and search for prey. 

The brown tree snake is abundant on Guam, with localized estimates 

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 is the blind snake (Ramphotyphlops braminus), a harmless 

nonnative snake that resembles a worm in size and shape.

Protecting People

Protecting Agriculture

Protecting Wildlife

Wildlife Services Factsheet

January 2011

Brown Tree Snake 

an Invasive Reptile

Wildlife Services (WS), a program 

within the U.S. Department of 

Agriculture’s Animal and Plant 

Health Inspection Service (APHIS), 

provides Federal leadership 

and expertise to resolve wildlife 

confl icts threatening the Nation’s 

agricultural and natural resources, 

human health and safety, and 

property.

WS’ activities on Guam focus on 

control and containment of the 

invasive brown tree snake. WS 

conducts an operational program 

aimed at preventing the spread 

of the snake from Guam and 

protecting vital economic and 

ecological resources on the island.

.

The invasive brown tree snake, 

primarily nocturnal, is an adept 

climber.
Damage 

The brown tree snake has caused extensive damage to 

Guam. It is responsible for numerous power outages 

across the island each year. An opportunistic feeder, 

eating whatever is available, this species has caused 

the extinction of most of Guam’s native forest birds and 

lizards. 

As native bird populations have declined on Guam, 

the snake now feeds on introduced lizards and birds, 

rodents, and bird eggs. In its native range, brown tree 

snake populations are kept in check through natural 

processes, such as disease, food competition, and 

predation. Similar processes likely occur on Guam, but 

they are inadequate to control the snake’s population. 

Confl icts with People 

Although brown tree snakes are abundant on Guam, 

most people rarely encounter a live snake. The snakes 

do not hang from trees in giant bunches, nor do they 

search out people to bite. Brown tree snakes may be 

attracted to residential areas by abundant rodents, 

lizards, poultry, or debris that serves as habitat for snake 

prey; they 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 buildings less attractive to brown tree snakes.

Wildlife Services Research and Operations

Since 1993, WS has conducted ongoing operations to 

reduce damage caused by the brown tree snake. WS’ 

National Wildlife Research Center conducts research 

to identify effective toxicants, repellants, and trapping 

methods. On Guam, WS has more than 60 personnel, 

including 17 canine-detector teams and 4 employees 

who manufacture snake traps. Using specially designed 

traps, hand capture, and oral toxicants, WS personnel 

remove an average of 7,000 brown tree snakes annually. 

In 2001, WS began integrating the use of acetaminophen (the active ingredient in many over-the-counter 

pain medications) in its efforts. WS research has shown 

acetaminophen to be an effective oral toxicant for the 

snakes. In 2010, WS conducted a pilot project involving 

aerial distribution of the toxicant in baits placed in the 

upper forest canopy where the snakes spend much of 

their time. 

These efforts resulted in the fi rst hatch and rearing 

of the endangered Marinas crow in the wild in 25 years; 

the project also helped increase populations of the endangered Marina grey swiftlet.

 

Preventing its Spread 

Without cooperative control efforts, the problems caused 

by the brown tree snake could spread. Snakes have 

been sighted on many other Pacifi c islands, possibly 

having arrived through cargo originating in Guam. 

Numerous sightings on the island of Saipan suggest a 

snake population may be established on this island too. 

Together, these sightings clearly demonstrate the risk of 

unintentionally transporting brown tree snakes to vulnerable locations and the potential for new populations to 

develop. 

WS conducts operations and research to identify effective toxicants, repellants, 

and trapping methods.

WS has developed the current standard 

for brown tree snake traps.
WS coordinates operational efforts on Guam to 

keep snakes from reaching other destinations. WS 

personnel trap snakes in high-risk areas, use trained 

snake-detector dogs in cargo, conduct night-time spotlight searches, and carry out public education efforts to 

achieve this goal. When departing Guam, residents can 

help prevent the brown tree snakes’ spread by carefully 

inspecting their belongings, especially outdoor goods, 

when packing.

Additional Information

For more information about the brown tree snake, 

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

Hawaii WS State offi ce at (808) 838-2841. You can also 

visit the WS Web site at 

www.aphis.usda.gov/wildlife_damage. 

The U.S. Department of Agriculture is an equal opportunity provider and employer.

Mention of companies or commercial products does not imply recommendation or endorsement by the USDA over others not mentioned. The USDA neither guarantees 

nor warrants the standard of any product mentioned. Product names are mentioned solely to report factually on available data and to provide specifi c information. 

United States Department of Agriculture

Animal and Plant Health Inspection Service

Canine teams are available to search cargo leaving the 

island to prevent the reptiles’ spread.