The brown tree snake 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 1–2 m (3–6 ft) 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. 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.