<P> The brown tree snake (Boiga irregularis) is a nocturnal, arboreal species that uses visual and chemical cues in hunting in the tropical rainforest canopy and / or on the ground . It is a member of the subfamily Colubrinae, genus Boiga, which is a group of roughly twenty five species that are referred to as "cat - eyed" snakes for their vertical pupils . The brown tree snake is generally between one and two meters (three and six feet) in length in its native range . The snake is long and slender, which facilitates its climbing ability and allows it to pass through tiny spaces in buildings, logs, and other shaded locations where it seeks refuge during daylight hours . Variations in coloration occur in the snake's native range, ranging from a lightly patterned brown to yellowish / green or even beige with red saddle - shaped blotches . They are rear - fanged, have a large head in relation to their body, and can survive for extended periods of time without food . </P> <P> The brown tree snake is a generalist feeder known to eat a wide variety of foods, when threatened is highly aggressive and tends to lunge and strike the aggressor repeatedly . The snake has numerous teeth but only the last two on each side of the upper jaw have grooves, which inject venom as it bites . Therefore, the snake's mouth must be opened as wide as possible to insert and expose their fangs . A chewing movement is used by the snake to inject the venom by means of capillary action along the grooved fangs . The venom is used to subdue and kill prey on which the snake feeds; however, the venom is not considered dangerous to adult humans . In addition to subduing its victim with its venom, the brown tree snake often wraps its body around the prey, like a constrictor, to immobilize the prey while chewing and consuming the animal . </P> <P> The brown tree snake is native to coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia . The species occurs on variably sized islands, extending from Sulawesi in eastern Indonesia through Papua New Guinea and the Solomon Islands and into the wettest coastal areas of Northern Australia . The snakes on Guam represent the only documented reproductive population outside the native range . Since January 2016, however, four snakes have been sighted on the island of Saipan in the Northern Mariana Islands . </P> <P> The brown tree snake is not restricted to forested habitats as it can also occur in grasslands and sparsely forested areas as well . In Papua New Guinea, it occupies a wide variety of habitats at elevations up to 1,200 m . It is most commonly found in trees, caves, and near limestone cliffs but frequently comes down to the ground to forage at night . It hides during the day in the crowns of palm trees, hollow logs, rock crevices, caves, and even the dark corners of thatched houses near the roof . Based on the frequency of sightings of this snake, in relation to buildings, poultry, and caged birds, the snake is considered to be common in human - disturbed habitats . </P>

Why are there so many snakes in guam