Guam’s snake population is dominated by a single, highly invasive species: the brown treesnake (Boiga irregularis). This nocturnal, tree-dwelling snake has become a significant problem for the island’s unique ecosystem and infrastructure since its accidental introduction, leading to widespread ecological disruption and economic challenges.
The Unwelcome Invader: Brown Treesnake
The brown treesnake (Boiga irregularis) is native to parts of eastern and northern coastal Australia, Papua New Guinea, and eastern Indonesia. It likely arrived on Guam accidentally as a stowaway in military cargo ships shortly after World War II, before 1952. Genetic analysis suggests an origin from the Admiralty Island group of northern Papua New Guinea, a region with large military bases during the war.
Most brown treesnakes on Guam average 1 to 2 meters (3 to 6 feet) long. Nocturnal and arboreal, they are active at night and primarily live in trees, though they can be found in various habitats. They are mildly venomous, possessing rear-fanged teeth, and also use constriction to immobilize prey. Females lay clutches of 3 to 12 leathery eggs in hidden locations like hollow logs or rock crevices and can reproduce year-round on Guam. This continuous reproduction, abundant prey, and few natural predators allowed their populations to reach unprecedented densities.
Ecological Collapse on Guam
The brown treesnake’s arrival on Guam triggered an ecological collapse due to its predatory impact on native species that evolved without snake predators. As an opportunistic feeder, it preys on birds, bats, lizards, and their eggs.
The brown treesnake is responsible for the extirpation or extinction of 10 of Guam’s 12 native forest bird species, including the Guam rail and kingfisher, which now exist only in captive breeding programs. The loss of these birds has had cascading effects, particularly impacting seed dispersal for native plants. Fewer birds to spread seeds may have significantly dropped new tree growth, altering forest composition. The snake has also severely affected populations of native lizards and bats.
Broader Impacts Beyond Wildlife
Beyond ecological damage, the brown treesnake invasion has inflicted substantial non-ecological consequences. Frequent power outages are a notable impact, caused by snakes climbing utility poles and shorting electrical equipment. These outages are a persistent problem, averaging 133 per year from 1991 to 1997. The economic costs are considerable, ranging in millions of dollars annually due to lost revenue and infrastructure damage.
Snakes also invade homes and commercial buildings in search of food or shelter. While mildly venomous, bites on humans are rare and typically not life-threatening, though infants under six months old may be at higher risk and should receive medical attention if bitten.
Combating the Invasion
Control efforts on Guam and prevention of spread to other snake-free islands involve various strategies by local and federal agencies, including the USDA and Department of Defense. Trapping is a primary method, often using live mice as bait. A novel approach involves dropping dead mice containing 80 milligrams of acetaminophen from helicopters onto infested areas. Acetaminophen is highly toxic to snakes, causing death within 24 hours by interfering with their blood’s ability to carry oxygen, while posing minimal risk to non-target species.
Detection dogs are employed at ports and cargo facilities to intercept snakes attempting to stow away on outgoing shipments. These trained canines effectively detect snakes in hidden compartments, significantly reducing accidental spread. Research also continues into biological controls and physical barriers to limit snake movement. These efforts are part of a cooperative program aimed at reducing snake populations on Guam and preventing their dispersal throughout the Pacific.
Coexisting and Preventing Spread
Residents and visitors on Guam can adopt practical measures to prevent brown treesnakes from entering homes and property. Precautions include keeping doors and screens securely closed and screening outdoor air ducts or pipes. Maintaining a tidy outdoor environment by removing debris and managing vegetation around buildings can also make an area less attractive to snakes.
Vigilance is crucial in preventing the brown treesnake from spreading to other vulnerable islands. Individuals traveling from Guam should thoroughly check luggage, cargo, and vehicles for hidden snakes. If a brown treesnake is encountered, report the sighting to local authorities or wildlife services, as trained personnel can safely capture and remove it. These collective actions help mitigate the snake’s impact on Guam and protect other Pacific islands from a similar invasive threat.