\r\nB. irregularis is rear-fanged and mildly poisonous. The snake’s venom trickles into a bite victim along grooves in the rear fangs; because of the relatively small size and position of the fangs, a brown tree snake must chew to allow the fangs to penetrate the skin (USDA-APHIS 2001). The brown tree snake will readily strike when aggravated, but it does not present a danger to adults. A bite from this snake will not penetrate most clothing, Both constriction and venom are used to help immobilize prey (USDA-APHIS 2001), and babies less than 6 months old may be at risk from both brown tree snake bites and constriction (USDA-APHIS 2001). A young victim of a brown tree snake bite should receive immediate medical attention.
Any snake sightings on islands thought to lack snakes should be reported immediately to:\r\n\r\n
James Stanford--USGS\r\n
Brown Treesnake Rapid Response Team Coordinator\r\n
Phone (24 hours): 671-777-HISS (4477)\r\n\r\n
Further information on reporting brown treesnake sightings is available at the \r\nUSGS Fort Collins Science Center site.
One puzzling result of brown tree snake reproductive studies is that reproductively active males appear to be relatively rare; this is surprising, because female reproductive activity occurs at all times of year in brown treesnakes (F. J. Qualls & C. P. Qualls Unpub. Data, Aldridge 1996 1998, Rodda \r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\net al. 1999c, in Rodda et al. 2002). From an adaptive perspective, one would expect males to be able to take advantage of mating opportunities at whatever time of year they encounter a receptive female. Yet reproductively-active males are relatively rare in samples of brown tree snakes (which are collected primarily with food-baited traps). One possible explanation for this phenomenon might be that snakes that are reproductively active are refractory to trap capture. Snake breeders report that male snakes in general avoid eating while they are in reproductive condition (N. Ford Pers. Comm., in Rodda et al. 2002).
Brown tree snakes shift their diet from smaller exothermic prey to larger endothermic prey as they grow from juveniles to adults (Savidge 1988). This is usually seen as a switch from lizards to birds and mammals. Skinks such as Emoia caeruleocauda and Carlia ailanpalai (itself an invasive species) and geckos such as Lepidodactylus lugubris and Hemidactylus frenatus (which are very abundant in human commensal areas) serve as a superabundant food source for juvenile brown tree snakes in Guam. High densities of introduced vertebrates, in particular, the gecko H. frenatus have allowed the snake to attain the high densities seen there (Rodda Fritts & Conry 1992).
Principal source: Rodda et al., 1999; Fritts & Leasman-Tanner, 2001; Mortensen et al., 2008
Compiler: Revision: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Dr. Gad Perry, Associate Professor, Conservation Biology Texas Tech University, USA.
Publication date: 2009-08-16
Recommended citation: Global Invasive Species Database (2024) Species profile: Boiga irregularis. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=54 on 07-10-2024.
Human Health: This rear-fanged colubrid snake is mildly venomous and poses a potential health hazard to infants and young children. It is responsible for one of every thousand hospital emergency room visits on the island (United States Department of Defense 2008). Envenomation of babies has been reported as relatively frequent (Fritts et al. 1990). Besides the direct effects of brown tree snake bites, there is also the danger of increased disease carried by insects that were previously kept in check by Guam's native lizards and birds (Fritts & Leasman-Tanner 2001). Examples of this include an outbreak of dengue fever carried by mosquitoes and a high rate of infant salmonellosis for several years (Fritts & Leasman-Tanner 2001).
Economic/Livelihoods: Power outages caused by snakes have been a serious problem on Guam since 1978, and the incidence of snake-caused outages continues to cause significant problems. The brown tree snake has caused thousands of power outages affecting private, commercial, and military activities, at one stage averaging once every two to three days. While most of these affect a limited area, some are widespread or island-wide blackouts. Everything from school lighting, computers used by retail outlets, traffic signals to refrigeration of perishable goods are subject to these power interruptions. The costs due to direct damages and lost productivity are conservatively estimated at $1 to 4 million dollars each year (Fritts & Leasman-Tanner 2001; Fritts 2002).
A bad perception of the brown tree snake (although it is not harmful to adults) may cause tourists to avoid Guam in favour of more unspoilt locations. Since tourism is only outranked by U.S. military and government in economic importance on Guam, lost tourism dollars could cause major economic stress (Fritts & Leasman-Tanner 2001). Researchers estimate that if the brown tree snake estabishes in Hawaii tourism losses will amount to USD 0.5 to 1.5 billion (D' Evelyn et al. 2008; Rodda & Savage 2007).
Agriculture: The brown tree snake is reported to be an agricultural pest (Fritts & McCoid 1991, in Engeman et al. 2002). Insect species that are no longer naturally controlled by Guam’s native birds and lizards reduce fruit and vegetable yields (Fritts & Leasman-Tanner 2001). Agriculture has continually declined in importance on Guam since 1945, around when the snake was introduced to the island (Fritts & Leasman-Tanner 2001). Agriculture has continually declined in importance on Guam since 1945, around when the snake was introduced to the island (Fritts & Leasman-Tanner 2001), although additional socio-economic factors were very important in this process.
Preventative measures: In 1993 Wildlife Services (WS) and the US Department of Agriculture began a programme to reduce the potential for snakes to enter Guam's transportation system (see Engeman et al. 2002; Vice et al. 2005b). WS has taken the primary role in this effort through trapping, oral toxicants, fence line searches and the use of BTS detection dog teams (Stanford & Rodda 2007).
Physical Control:
Traps: A variety of modified crawfish or minnow traps have been used on Guam to trap snakes (Rodda et al 1999; Vice et al 2005a). Trapping snakes with live-mouse lures is the principal control technique for this invasive species on Guam (Gragg et al. 2007). It is estimated that approximately 2500 snake traps have been placed on the island (Rodda et al. 2002).
Barriers: Multiple studies have examined the use of barriers for blocking brown treesnakes (Rodda et al. 1998; Perry et al. 2004). Rodda and colleagues (2002) found it possible to create small, predator-free nature reserves using a combination of snake barrier and trapping methods (Rodda et al. 1999a). Campbell (1996, in Rodda et al. 2002), eliminated brown tree snakes from two one-hectare plots and found that lizard species showed a dramatic increase in abundance compared with similar snake-inhabited plots; within a year their numbers roughly doubled. The Campbell barriers brought attention to two acute problems: typhoons and rats. Rats chew holes in all things chewable and Guam is subjected to irregular but severe cyclonic storms which may damage barriers (Rodda et al. 2002).
Chemical: One component of brown tree snake management on Guam is the use of a toxic bait that consists of acetaminophen tablets inserted into a dead newborn mouse, which in turn is placed within a cylindrical polyvinyl chloride bait station suspended above ground or fitted with a tiny parachute so that it drifts into trees (Avery Tillman & Savarie 2004; Savarie et al. 2005; Westbrook and Ramos 2005). Possible hazards to nontarget species, especially the Mariana crow (Corvus kubaryi) which ingests mice, are of concern but appear to be limited (Avery Tillman & Savarie 2004).
Thermal: Brown treesnakes can be killed by excessively cold or hot temperatures, and several studies have examined the use of thermal fumigation. Under normal handling conditions, passive thermal fumigation might have some benefits, but is not a complete solution (Perry & Vice, 2008).
Biological Control:\r\nHistorical evidence shows that the biological control of vertebrates is fraught with unacceptable risk. Cane toads and poisonous red-bellied black snakes may prey on the young of the brown tree snake occasionally but the introduction of either could conceivably cause more problems than it could potentially solve (Caudell et al. 2002).
Integrated Pest Management (IPM):\r\nConservation actions on Guam should be directed towards an improved recruitment via artificial pollination and planting of flora indirectly impacted by the brown tree snake (see Ecology Page Impacts information from Mortensen et al. 2008). Restoring conditions for natural pollination or managing reproduction of vertebrate-pollinated plants is critical in the long-term conservation of native vegetation types on Guam (Mortensen et al. 2008). Efforts are now underway to conserve the few remaining larger areas of uniform forest vegetation, e.g. the conservation action plan Guam Comprehensive Wildlife Conservation Strategy (2005).