Boiga irregularis (Merrem, 1802)
Family: Colubridae Brown Treesnake Status: Invasive Description: The Brown Treesnake is a medium sized to large snake. It is slender for it length and has large protuberant eyes with a vertical pupil. Animals from Guam attain a greater length than elsewhere in their native range (Savidge et al. 2007). The largest individual that the author has observed was 1950 mm SVL and 2300 mm TL. Snakes of this size are uncommon and most observed are less than a meter long. As suggested by the name, the brown treesnake is invariably a shade of brown though there is some variation from light yellow/tan to dark green/brown. Large adults tend to be darker than juveniles and sub-adults and males tend to be lighter and less patterned than females (pers obs). There is often a series of darker bands that are most prominent on the anterior portion of the body. The lips and chin and anterior portion of the belly are yellow. Biology: On Guam, the brown treesnake occurs island wide in every habitat including, but not limited to, developed urban areas, beach strand vegetation, limestone forest, disturbed and secondary forests and treeless savanna. It feeds on most vertebrates that are small enough to consume. Food trash such as chicken and bloody packaging are occasionally sought out and eaten. On Guam, geckos and skinks form the bulk of its diet. In the past, brown treesnakes occurred at extremely high densities, up 100 individuals per hectare (Rodda et al 1992). Since that time, both bird and small mammal populations have crashed (due to over predation) and currently snakes are both smaller and less numerous then they were at their peak in the late 1980’s. There have not been any recent density estimates, but Boiga irregularis is still very common on Guam. Though common, its nocturnal habits and cryptic coloration make it difficult to observe unless a dedicated effort is made. The brown treesnake is mildly venomous. There are enlarged teeth located far back in the mouth used to convey venom into a bite by way of a groove. Because of the relatively small teeth, inefficient venom delivery system, and weak venom (to humans), this snake is not dangerous to anybody except the very young, very old, or the infirm. The author has been bitten several times with no more reaction than to that of a bite from a similarly sized non-venomous snake. Distribution: The brown treesnake is native to north and east Australia, New Guinea, the Solomon Islands, and Sulawesi. It was accidentally introduced to Guam shortly after WWII in cargo shipments originating from the Solomon Islands. On Guam it has played a significant role in the decline, extirpation and extinction of most of the native forest birds, at least one of the native bat species, and several species of lizard.(Savidge 1987, Rodda and Fritts 1992) Currently, there are considerable measures in place to prevent the spread of the brown treesnake from Guam to the rest of the Mariana Islands and beyond. Despite these measures, snakes originating from Guam have been found on Hawaii, Tinian, Rota, and Saipan. In the past two decades there have been over 70 reported sightings on Saipan, at least a few of which are credible. Rodda, G. H. and T.H.Fritts. 1992.The Impact of the Introduction of the Colubrid Snake Boiga irregularis on Guam's Lizards. Journal of Herpetology 26 (2) pp 166-164 Savidge, J.A.1987. Extinction of an island forest avifauna by an introduced snake. Ecology 68:660-668. Savidge, J. A, Qualls, F. and Rodda, G. 2007. Reproductive Biology of the Brown Tree Snake, Boiga irregularis (Reptilia: Colubridae), during Colonization of Guam and Comparison with That in Their Native Range. Pacific Science 61(2):191–199 |