The brown tree snake, Boiga irregularis, is an arboreal snake, meaning it spends the majority of its life in trees or otherwise off the ground. It measures up to 6.5 feet (2 m), with an average length of 4.5 feet (1.4 m). The brown tree snake is native to the tropical and subtropical regions of Australia, Papua New Guinea and the northwestern Melanesian islands.
This type of snake can also be found on Guam but is not native to the island and is considered an invasive or alien species. It was accidentally introduced to Guam shortly after the end of World War II. One theory is that the snake was accidentally brought to Guam along with a consignment of military equipment from the military bases on the Admiralty Islands of Papua New Guinea. This theory is supported by the Guam snakes' coloration and scale patterns, which most closely resemble those of the Admiralty Islands.
The invasive population of the brown tree snake has caused immense ecological damage on Guam. By 2010, this invasion had resulted in the extinction of nine of the island's 12 forest bird populations, half of its lizard species and possibly some of its native bat species. The threat to the island's remaining native species is ongoing. In its natural habitat, the population of this snake is naturally controlled by disease, predation and competition. These same factors exist on Guam, but they occur at a much lower rate and do not provide adequate population control.
The brown tree snake also causes extensive economic problems on Guam and has had a negative impact on Guam's human population. The snakes tend to travel along power lines on the island, causing frequent power outages. The venom of the brown tree snake is only mildly poisonous and is conducted by large, ridged rear teeth instead of fangs. It is not considered particularly dangerous to adults, because the snake must chew on its victim for some time before the venom is able to penetrate the skin. This is more of a threat to human infants, who have been known to suffer respiratory arrest as a result of envenoming.
The brown tree snake not only envenoms its prey but is also a constrictor, suffocating its prey by coiling its body tightly around its victim until the victim dies from lack of oxygen. The diet of the brown tree snake consists of birds, eggs, small mammals and small reptiles. The species is primarily nocturnal and spends daylight hours coiled in shaded tree canopies, bushes or rotted logs. This snake, although primarily arboreal, forages for food on the ground under the cover of darkness.