The Brown Tree Snake (Boiga irregularis) is one of the world’s most damaging invasive species, fundamentally altering the ecology of the Pacific islands it has colonized. This slender, nocturnal, arboreal predator spread unchecked for decades following its introduction to new territories. The species exemplifies how a single, accidentally introduced predator can lead to widespread biological and infrastructural devastation in environments lacking natural controls.
Native Habitat and Range
The Brown Tree Snake is native to a broad geographical area spanning parts of Oceania and Australia, where its population is naturally regulated by predators and competition. Its indigenous range extends from the wet, coastal areas of northern and eastern Australia (including Queensland and the Northern Territory) north into New Guinea. It is also found throughout eastern Indonesia, on islands such as Sulawesi and Papua, and across many islands in northwestern Melanesia, including the Solomon Islands.
In its native environment, the snake inhabits a variety of landscapes, including lowland woodlands, coastal forests, and tropical rainforests, at elevations up to approximately 1,200 meters. The snakes transported to other Pacific islands are believed to have originated from a specific population in the New Guinea area, most likely the Admiralty Island group.
The Mechanism of Invasion
The accidental introduction of the Brown Tree Snake to Guam is the most famous example of its spread, initiating shortly after World War II. Researchers estimate the snake first arrived between the late 1940s and 1952, a period marked by heavy military traffic and the salvage of wartime materials. The primary mechanism of transport was as a passive stowaway in surface cargo shipments, particularly military equipment and supplies moved from staging areas like Manus Island near Papua New Guinea.
The snake’s ability to conceal itself easily in crates, aircraft wheel wells, and structural gaps, coupled with its capacity to survive long periods without food or water, made it an ideal candidate for accidental transport. Initial sightings on Guam clustered near the U.S. Naval port facility in the Santa Rita area, suggesting the port was the point of entry. The introduction was likely not a single event but involved repeated translocations, leading to a robust and genetically diverse population that spread rapidly.
Ecological and Economic Consequences
The arrival of the Brown Tree Snake on Guam initiated a profound ecological collapse because the island’s native fauna had evolved without natural snake predators. The snake’s voracious feeding habits led to the near-total extinction of Guam’s native forest bird population. Of the island’s 12 native forest bird species, 10 were locally extinct, and the populations of the remaining two were severely reduced. The snake also caused significant declines in native lizard species, such as geckos and skinks, and two of Guam’s three native bat species.
This loss of native seed dispersers and pollinators triggered secondary ecological effects, leading to changes in the island’s plant communities and forest structure. With the native prey base depleted, the snake population shifted its diet to introduced species, such as rats and lizards. Despite this shift, snake density on Guam reached staggering numbers, estimated at one point to be as high as 30,000 snakes per square mile in some areas.
Beyond the environmental devastation, the snake has inflicted significant economic damage by interfering with the island’s electrical infrastructure. The snake’s habit of climbing power poles and electrical lines causes frequent short circuits, leading to numerous power outages across the island each year. Between 1991 and 1997, the island experienced an average of 133 snake-caused power disruptions annually, resulting in substantial financial losses. Ongoing control efforts, including cargo inspections at ports and airports to prevent the snake’s spread to other islands like Hawaii, cost millions of dollars annually.