Download Fact Sheet - Water Scorpion - Moreton Bay Regional Council

Water Scorpion
Laccotrephes tristis
Description
Defining feature: Comparatively large freshwater bug with a broad, leaf-like body ending in a
long respiratory siphon. Its pincer-like forelegs – adapted for seizing prey – together with the
siphon led to the common name Water Scorpion. However this insect has nothing to do with
scorpions (which are related to spiders) and is entirely harmless to humans.
Physical description: The blackish-brown Water Scorpion is some 60 mm long. Females have
a larger body than males (f: 31-36 mm; m: 26-32 mm) but their siphon is shorter (f: 26-33
mm; m: 30-35 mm), and the experienced observer can distinguish male and female with the
naked eye.
Habitat
Water Scorpions live at the edge of stagnant and running waters often in shallow muddy
places, but also in rock pools hidden among submerged leaf litter or occasionally among
water plants. The species is found in all sorts of waters from farm dams exposed to full
sunlight to shaded forest streams.
Feeding
A sit-and-wait predator in the shallow, the Water Scorpion sits – covered with mud or
concealed among fallen leaves – waiting for prey, head and pincer-forelegs directed towards
the deeper water. It feeds on various kinds of aquatic worms and insect larvae, and also
hunts for tadpoles and small fishes.
Mosquito larvae appear to be a favourite prey and Water Scorpions could be used for
mosquito control in garden ponds. Successful mosquito control in urban small waters has
been reported from Asia (different species of Laccotrephes) when using juvenile Water
Scorpions, which are wingless. Adults seem to be strong fliers and tend to leave small water
bodies.
Breeding
Limited information available.
Conservation
Status: Aquatic invertebrates are not listed under State and Federal Government
environmental legislation. This is due to the lack of knowledge about this species-rich
component of Australia’s fauna.
Additional information
In Australia only one species of Water Scorpions occurs. Laccotrephes tristis belongs to the family
Nepidae of the insect order “true water bugs” (Heteroptera).
Sources: Andersen N.M. & Weir T.A. 2004. Australian Water Bugs - their biology and identification. CSIRO Publishing/Apollo Books, 344
pages. Photograph by Ulrike Nolte.
Distribution
The Water Scorpion is found throughout
Australia except Tasmania. It is common in
the Moreton Bay Region due to the many
man-made dams and ponds that increase
the extent of suitable habitat.
Legend:
Known distribution based
on species records
Moreton Bay Regional Council boundary