Taxonomic name: Boiga irregularis (Merrem, 1802)
Synonyms:
Common names: Braune Nachtbaumnatter (German), brown tree snake (English), brown treesnake (English), culepla (Chamorro-Guam), kulebla (Chamorro-Guam)
Organism type: reptile The night-loving and tree-loving, brown tree snake (Boiga irregularis) is secretive by nature. It is often found concealed on container ships and in aircraft cargo. It probably arrived on Guam after World War II in a cargo ship. Now the wetlands, coastlands and forests of Guam are bereft of nine out of twelve native bird species (and two out of eleven native lizards) due to the snakes voracious appetite. The brown tree snake is not a fussy feeder, stimulating the very real fear that it might drive yet more species to extinction. Description
The brown tree snake (Boiga irregularis) is a slender snake with large eyes and a broad head (much wider than the neck). It is light brownish to yellowish olive in colour and occasionally a shade of greenish brown. Black speckling may be present. The pupil of the eye is vertical. The brown tree snake may reach a length of three metres but is typically only one to two metres long. It is a climbing snake and may be aggressive when cornered Occurs in:
agricultural areas, coastland, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, wetlands Habitat description
The brown tree snake (Boiga irregularis) occurs in a wide variety of habitats and environments, which is evidence of its great adaptability and which explains why it is such a high-risk invasive species.
In Indonesia (part of its native range) Boiga irregularis is found in tropical evergreen forests, montane forests, lowland tropical forests, mangroves, montane savanna, wet savanna, seasonal dry forests and closed shrubland. In Indonesia it is also found in human-modified environments, such as deforested land, grassland and croplands (coffee, rice and rubber plantations as well as coconut, tea and maize growing areas) (Perry, Dr. G.).
In Guam the brown tree snake is found in all terrestrial habitats, but is especially common in forests and human-modified environments (Rodda et al).
In the Northern Mariana Islands, the brown tree snake occurs in freshwater swamp forests, herbaceous wetland vegetation, tropical montane savanna, coastal strand vegetation and mangrove forest. It also occurs in human-modified environs: grassland, pasture, cropland (coconut, coffee, rice, sugar cane and rubber) and deforested land. General impacts
An effective generalised predator, the brown tree snake (Boiga irregularis) has decimated the Guam avifauna, greatly impacted other terrestrial vertebrates and caused cascading ecological perturbations. It is likely to similarly destabilise ecosystems if established elsewhere. It is a human nuisance and an agricultural pest. Geographical range
Native range: The brown tree snake (Boiga irregularis) is native to eastern Indonesia, the Solomon Islands, New Guinea, as well as the northern and eastern coasts of Australia.
Known introduced range: It has been introduced to Guam and the Northern Mariana Islands. Brown tree snakes have also been sighted on Saipan, Tinian, Rota, Kwajalein, Wake Oahu, Pohnpei, Okinawa and Diego Garcia. To date, Boiga irregularis is not known to be established on any of these islands, except Guam, but frequent reports of snake sightings on Saipan evidence the presence of snakes on the island. In the United States incursions by B. irregularis have been repeatedly intercepted. Introduction pathways to new locations
Aircraft: The brown tree snake (Boiga irregularis) can lie hidden in both wheelwells and cargo of ships.
Military: The original mode of introduction of the brown tree snake (Boiga irregularis) was as a stowaway in military equipment and cargo. Currently, it is sometimes associated with large-scale exercises and personal cargo of personnel moving from Guam to other duty posts.
Seafreight (container/bulk):
Local dispersal methods
Natural dispersal (local):
Road vehicles: As stowaways in various compartments.
Translocation of machinery/equipment (local): Mostly household, but could be heavy machinery as well. Management information
In 1995 the brown tree snake (Boiga irregularis) was listed by the US Department of Agriculture as among the top three pests requiring control and eradication (Source: SPREP). No large-scale eradication programmes have been employed, however, traps, visual inspections, trained dogs and specialised barriers are in use. Toxicants and bio-control are in development. Efforts are being made to develop artificial attractants. Snake barriers have been used in some situations; vinyl barriers are durable, but the surface finish may degrade over time. Surfaces must be smooth to deter the snake from attempting to climb the barrier. Masonry barriers use a pre-stressed moulded concrete design which is 100% successful in keeping snakes out and is not vulnerable to rat or typhoon damage. However, it has a high initial cost of approximately US$300 per metre. There are currently approximately 2500 snake traps on Guam (Rodda et al. 2002).
Guam's importance as a trans-Pacific shipping hub, coupled with the tendency of snakes to seek refuge in cargo make snake dispersal from Guam a serious threat to other island ecosystems (Fritts 1988; Fritts et al. 1999; Vice et al 2003; Vice Engeman and Vice 2005). Because of this, the major mission of Commander Naval Forces Marianna Naval Base, Guam is to ensure the brown tree snake does not move to other islands. If it moves to Hawaii or the mainland it is considered to reek havoc (Westbrook and Ramos 2005). Brown tree snakes can easily hide in ships moving between islands and are currently being moved to new islands in aircraft cargo. Several tree snakes have been detected at Honolulu airport in recent years. Preventing their spread depends on the maintenance of continuous checking of ships and aircraft cargo. Detector dogs are in use in the Northern Mariana Islands (Perry 1998). The Global Invasive Species Programme (GISP) is fostering a cooperative effort among experts in Guam, Australia, Hawaii and mainland USA in an effort to combat this pest.
A variety of snake traps have been used on Guam; most consisting of a modified crawfish or minnow trap, housing a live mouse that serves as a lure (Vice Engeman and Vice 2005). The traps are hung on vegetation or along security fences (Vice Engeman and Vice 2005). New techniques are also being developed, such as "pinkies with parachutes", which consist of deceased newborn mice filled with acetametaphine and fitted with tiny parachutes that allow them to drift into trees. As the brown tree snake is arboreal it is more likely to come across the mouse if it is in the tree and, because it has a parachute, the bait may land in positions that would be inaccessible to humans setting traps from the ground (Westbrook and Ramos 2005). Nutrition
The brown tree snake (Boiga irregularis) feeds on birds, lizards, small mammals (including bats), bird and reptile eggs and domestic animals (small pets) (Westbrook and Ramos 2005). Juveniles mainly feed on lizards and amphibians (in particular, frogs) while adults prefer larger animals (birds, mammals). Reproduction
The brown tree snake (Boiga irregularis) lays eggs in clutches of 10 or more in their native range and in clutches of five in Guam. In ideal conditions it reproduces year-round, but in temperate environments reproduction is seasonal. Females may be able to store live sperm for several months. Lifecycle stages
Incubation of eggs lasts about three months. The brown tree snake (Boiga irregularis) is a highly mobile climber and stowaways on planes and boats are mostly juveniles. Movement may be aggravated by decreased prey availability. This species has been nominated as among 100 of the "World's Worst" invaders Reviewed by: Major update under progress
Dr. Gad Perry, Dept. of Zoology, University of Wisconsin, Madison, USA.
Compiled by: Dr. Gad Perry, Dept. of Zoology, University of Wisconsin, Madison, USA.& IUCN/SSC Invasive Species Specialist Group (ISSG)
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Last Modified: Wednesday, 16 August 2006
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