The Brown Tree Snake, Boiga irregularis, belongs to the snake family Colubridae. The genus Boiga contains about 25 species. This group of snakes (Boiga) is referred to as "Cat-eyed" snakes due to the pupil being vertical like a cats eye. Several are in Africa but the majority are native to Asia and Southeast Asia. The Brown Tree Snake is a native of Australia, New Guinea and the islands surrounding New Guinea. It is thought that the Guam Brown Tree Snakes originated on the island of Manus, a small island in the Solomons.

The distinguishing characteristics for the brown tree snake are the vertical pupil, the rear fangs, a large head in relation to the body, and a brownish or greenish color. Sometimes faint bands can be seen on the body. The coloration and the bands can be somewhat variable throughout the native range.

The snakes are about 18 inches long after hatching. Adults are generally 4 -5 feet long and as big around as an adult humans’ thumb. On Guam snakes in excess of 9 feet have been captured. Juveniles, up to about 3 feet in length eat lizards exclusively. Adults switch over to warm blooded prey, rats, mice, shrews, birds and bird eggs.

Venom is delivered into the prey animal by repeated action of the enlarged rear teeth/fangs. The fangs have a groove and the venom runs through the groove into the wound. It is a mild venom roughly equivalent to a bee sting in an adult human, although babies that have been bitten have had to be hospitalized. There have been no deaths from a Brown Tree Snake bite. How well the venom subdues a prey animal or if it is more of a digestive aid is not really known. Larger snakes will use constriction to subdue larger prey.

Reproduction is poorly known. Females can lay up to 14 eggs it is believed. On Guam the snakes can probably breed year round. It is not known if females can lay more than one clutch per year. The eggs hatch in 90 days. The snakes are around 3 years old when they first reproduce. Females can probably store sperm for several years. Meaning they can mate with a male, lay fertile eggs and then lay another fertile clutch of eggs 2 years later from that same male. This has been documeted in zoos with other species of Cat-eyed snakes.