What is the brown treesnake?

The brown treesnake is native to parts of Indonesia, the Solomon Islands, New Guinea, and Australia. The snake was first sighted on the island of Guam in the 1950s, probably after stowing away on cargo ships coming from New Guinea. In 2020, a population of brown treesnakes was discovered on Cocos Island, a small atoll of the southern shore of Guam, which represents the first instance of brown treesnakes establishing off the island of Guam.

The snakes feed on lizards, birds, small mammals, and eggs. Since the treesnake has no natural predators or other controls on Guam, it multiplied rapidly and has virtually wiped out Guam’s native forest birds. The snakes also crawl on electrical lines and cause expensive power outages and electrical damage.

Brown treesnakes are mildly venomous. While the snakes are not considered dangerous to an adult human and no known deaths have occurred, young children can have reactions to tree snake bites.

Many techniques have been discussed to eliminate the brown treesnake in Guam, but there is no known way to remove them entirely. The best management strategy is to keep them from becoming established at new locations while continuing to do research on tools such as improved traps, fumigants, toxicants, and attractants; and on control options such as parasites and viruses.

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Date published: November 5, 2020

Invasive Brown Treesnake Present on Cocos Island, Agencies Working to Prevent Further Spread

For the first time, an invasive brown treesnake population has been found on Cocos Island, an 83.1 acre atoll located 1.5 miles off the southwest coast of Guam.  

Date published: May 22, 2020

USGS Brown Treesnake Research Continues at Guam National Wildlife Refuge

On May 14, Director Reilly signed a Memorandum of Agreement with the Department of the Navy and the U.S. Fish and Wildlife Service. The MOA provides for continuity of operations for the USFWS and the USGS with construction of new office and lab facilities on the Guam National Wildlife Refuge in conjunction with DOD’s construction of a Marine Corps firing range.

Date published: January 23, 2020

New Study Provides Insights for Detecting the Invasive Brown Treesnake

Research by the USGS and Dickinson College reveals why scientists fail to detect brown treesnakes at low densities

Date published: March 3, 2016

Brown Treesnake Rapid Response Team Deployed to Saipan after Two Snake Sightings

Two recent reports of two brown treesnakes on Saipan is prompting federal and state officials to urge citizens of Hawaii, Guam and other Pacific Islands to report any sightings of these invasive snakes to authorities. Snakes can be reported by calling (671) 777-HISS or (670) 28-SNAKE.

Date published: November 7, 1997

Snake Barrier On Rota is Important Step Toward Preventing Future Spread of Brown Tree Snake

A new way to prevent brown tree snakes from invading was unveiled yesterday by scientists working for the U.S. Department of the Interior’s U.S. Geological Survey and Ohio State University.

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Scientist holding brown treesnake
October 21, 2020

Scientist holding brown treesnake

A USGS scientist holds an invasive brown treesnake.

Brown Treesnake Consumes Gecko
September 29, 2018

Brown Treesnake Consumes Gecko

Juvenile Brown Treesnakes (BTS) prefer to eat cold-blooded species like geckos and skinks. This snake was encountered consuming a locally abundant gecko, also thought to be a human introduction to Guam. The abundance of nonnative prey on Guam supports BTS populations and poses challenges to suppression of snakes for native species recovery. 

Invasive brown treesnake
November 12, 2010

Invasive brown treesnake

Brown treesnakes were a major contributor to the loss of nine of 11 native forest birds on Guam.

A brown treesnake in a Streptopelia bitorquata (island collared dove) nest. Yona, Guam, 2009.
December 31, 2009

A brown treesnake in a Streptopelia bitorquata nest

A brown treesnake in a Streptopelia bitorquata (island collared dove) nest. Yona, Guam, 2009. Photo by James Stanford, USGS.

Brown Treesnake Eating a White Tern

Brown Treesnake Eating a White Tern

A Brown Treesnake (BTS) eating a white tern on northern Guam. This observation was made during ongoing field work to refine snake control strategies in military housing. Snakes are capable of consuming very large prey items, and the snake successfully swallowed the tern. The Department of Defense maintains ongoing BTS interdiction efforts to control the abundance of BTS on

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Up close view of Brown treesnake in grass

Brown treesnake in grass

Brown treesnake in grass.