Biology Reference
In-Depth Information
4.4 Aberrant Cases and Representative Cases Without Clear
Etiology: A Critical Assessment of Risk
Things seen are mightier than things heard.
Lord Alfred Tennyson (1864)
4.4.1
Boiga irregularis
4.4.1.1 Background, History, and Aberrant Features of Bites
Boiga irregularis
(Plate 4.9A-D) presents a unique and unusual opportunity to assess
the medical importance of a non-front-fanged colubroid species. This is due to the rela-
tively large number of medically reviewed snakebite incidents associated with this spe-
cies, as well as the atypical circumstances surrounding its clinical importance.
Introduced to Guam (probably from Papua New Guinea) during the extensive
ordinance transport operations in the Pacific Theater of World War II,
B. irregularis
rapidly established growing populations partly due to a lack of any natural predators.
The burgeoning numbers of snakes had a severe impact on some of the native wildlife,
especially birds (some species, including the endemic Guam rail,
Gallirallus owstoni
,
and the Micronesian kingfisher,
Halcyon cinnamomina
, were extirpated), fruit bats
(e.g., the Marianas fruit bat,
Pteropus mariannus
), and probably a number of scincid
and gekkonid lizard populations [e.g., the scincid,
Emoia caeruleocauda
(Pacific blue-
tailed skink) the gekkonid,
Gehyra mutilata
(four-clawed gecko or stump-toed gecko),
and others;
www.mesc.usgs.gov/resources/education/bts/impacts
]. The decrease and
disappearance of bird populations in the 1970s was the first worrying sign of the
devastating ecological impact that this snake would cause in the coming decades on
Guam, Saipan, Marianas, and other islands. In recent years,
B. irregularis
populations
on Guam have often reached densities exceeding 50 snakes/hectare (
http://www.
Boiga irregularis
is the only ophidian species ever to be targeted for control mea-
sures by an act of the United States Congress (e.g., Brown Tree Snake Control and
Eradication Act of 2003, H.R. 3479, November 7, 2003).
In addition to its impact on native wildlife,
B. irregularis
rapidly affected the human
inhabitants on Guam. This species has a predilection for frequent copulatory behavior,
and predation on nestlings or scavenging birds electrocuted on power lines (Fritts and
McCoid, 1999; see
Plate 4.85A and B
). From 1978 to 1994, this behavior resulted in
numerous electrocutions of these snakes that caused approximately 1,200 power out-
ages (“brownouts”) on Guam (Fritts and McCoid, 1999). These incidents cumulatively
resulted in a significant economic impact on the island's economy (Fritts and McCoid,
1999; Fritts et al., 1990, 1994). These snakes also actively preyed on domestic animals
and, occasionally, ingested pet food left for dogs or cats (Fritts et al., 1994, 1999).
The medical importance of
B. irregularis
on Guam became evident during
the mid-1980s to the late 1990s, when approximately 50 emergency visits per
annum (about 1/1,200 emergency-room visits) were due to bites from
B. irregularis
