The Ordgarius magnificus, or bola spider has a very sophisticated
technique to capture prey. By day, it hides in a silk lined retreat
among the leaves of native trees such as eucalypts. At night, the
mature female spider hangs head down from a horizontal silk strand,
and using an extended front leg, she suspends a silken thread about
4 cm long, with a sticky globule at the end (the bolas).
This sticky globule contains chemicals that act as a female moth
perfume to lure male moths of a certain species. Like a fishing
line, the silk comes from her spinnets (the reel), and can be let
out when required, running through the claws on her leg. In
response to the vibrations of an approaching male moth, the spider
begins to jerk its body so as to swing the bolas around in a
circle.
When the moth is close, she lets the thread run and then flicks it,
with incredible accuracy, to hit the moth. The confused male moth
is then entangled and the spider winds it in, wraps it in silk and
eats it. In this species of spider, different perfumes, or
pheromones, are used for different seasons or growth stages, to
capture the moth species that are available, or those of the best
size.
By Tracey Churchill (CSIRO Sustainable Ecosystems, Darwin)
