U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Published by U.S. Department of Interior, Office of Insular Affairs for the Brown Treesnake Control Committee. March 2005.


Preventing spread of the brown treesnake (BTS) from Guam and mitigating its impacts on Guam are national responsibilities for the United States. BTS very likely arrived at Guam’s major harbor shortly after World War II with salvaged war materials returned from strategically crucial military operations in 1942-45 on islands near New Guinea, where BTS is native. Though this scenario is not 100% confirmed, it is rare to find a biological invasion for which there is such strong evidence of the source, pathway, and timing. BTS invaded the whole of Guam over several decades. In conjunction with research into the rapid loss of Guam’s native birds, the discovery was made that BTS occurs on the island at remarkably high population densities (up to 40/acre versus less than 1/acre in their native range). The treesnake invades Guam airports and harbors in search of prey and occupies a variety of habitats. The nocturnal BTS hides during the day in crates, vehicles, and other materials that are commonly moved by air and sea to other islands. It can survive for months without food. Guam is a transportation hub for civilian and military traffic in the western Pacific. Individual snakes have traveled as far as Japan, Okinawa, Wake Island, Hawaii (Oahu), Alaska, Texas, Spain, and Diego Garcia. The species may already be established on Guam’s neighbor island, Saipan, and individual snakes have been found on nearby Tinian and Rota. Consequences of BTS invasion have been devastating to the biological diversity and human infrastructure of Guam (an area of 209 square miles with a population of 135,000). BTS would clearly precipitate a biodiversity and economic crisis through establishment and population expansion on any other tropical or warm-temperate island in the world outside its native range. There is no question about the magnitude of the risk involved; the snake has the potential to damage infrastructure and eliminate not just endangered birds but virtually all island bird populations wherever it establishes.