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Genus/Species

 

Boiga spp., in particular: Boiga irregularis, Brown tree snake

Clinical entries

Species

  • 1. Boiga irregularis

Taxonomy

Serpentes; Colubridae; Boiginae

Common names

Cat snakes, Nachtbaumnattern

  • 1. Brown tree snake

Distribution

The genus Boiga is widespread in the Asian and Australian tropics.

B. irregularis: coastal areas in northern Australia, New Guinea, on several islands of eastern Indonesia and the Solomon Islands. Introduced onto Guam in more recent times. Likely to become established on other Pacific islands, including Hawaii. 

Biology

Approximately 28 species. Arboreal and nocturnal. Length of 13 m, depending on the species. Slender body which is laterally compressed. Head large and rounded, quite distinct from the neck. Large eyes with vertically elliptical pupils. Enlarged, grooved teeth at the rear of the maxilla. With a length of up to 3 m, B. irregularis is one of the largest species. Very slender body. Variable body colouring, sometimes with faint cross bands.

After the Second World War, this species was introduced onto Guam by visiting cargo ships. Due to the lack of natural competition (the only snake originally native to Guam is a burrowing species which lives underground), the B. irregularis population increased at an explosive rate. The population density is currently estimated to be around 13,000 per square mile! This species has practically wiped out the native birdlife on Guam, and some other vertebrates are highly endangered. B. irregularis are responsible for many power cuts on Guam, due to their habit of climbing electricity poles and short-circuiting the wires. From May to August each year, between 32 and 50 power cuts are caused solely by the Brown tree snake! Attempts to control these snakes have so far proved futile. Nonetheless, their population density is declining in certain areas due to the reduced food supply.

On Guam, the Brown tree snake is frequently found close to human habitations, and it will also enter houses.  It is known for its habit of killing and trying to devour prey that is too big for it. There have been several cases of people being bitten while they slept, in particular babies and children. On occasion, parents have discovered a Brown tree snake wrapped around their screaming child and chewing on the child's head or limbs. 

Risk

Although B. irregularis is quick to bite when threatened, these defensive bites, where the snake releases its victim immediately after the bite, lead to mild local reactions at worst. A bite is only dangerous if a sufficient amount of venom is injected through prolonged chewing motions. Cases of life-threatening envenoming have only been known to occur in children on Guam. In the other regions in which it is found, B. irregularis is considered harmless.

Cases of envenoming with local symptoms have also been reported for B. barnesi, B. ceylonicus, B. trigonata and B. dendrophila. 

Literature (biological)

Fritts et al. 1987, 1990, Minton 1990b, De Silva 1990, Collins 1991