Posted by Alan Bellows on September 7th,
2005 at 11:35 pm
In the forests of Costa Rica, there lurks a sinister variety of
wasp, bent on hijacking the minds of hapless spiders for its own
ends. Left unmolested, a variety of orb spider known as "Plesiometa
argyra" spends every day of its life carefully reconstructing its
perfectly round web, and feasting on the insects unfortunate enough
to become snagged upon it. But should one of these spiders fall
victim to this as-yet-unnamed species of wasp, the spider is
stripped of its free will, and made to spend the last evening of
its existence building a protective shelter for the larvae that
infect it.
It is a true example of mind control in nature, and though
scientists are well aware of the method of infection, they are
uncertain exactly how the mind control is accomplished. When a wasp
successfully attacks a host spider, the spider is temporarily
paralyzed as the wasp lays eggs on the tip of the spider's abdomen.
Once the wasp departs, the spider regains its ability to move, and
it continues its daily web construction for the next two weeks as
though nothing has changed. Meanwhile, the wasp's growing larvae
cling to the spider's belly and feed on its juices through a number
of small punctures.
On the night before the parasites kill their host, events take a
bizarre turn. Through some unknown mechanism, the larvae compel
their host spider to build a web that is very different from that
it has always constructed before. Instead of a flat, round web, the
spider builds a stout, reinforced platform which is much smaller.
Once the new web is complete, the larvae kill their host, and
cocoon themselves on the structure. It is ideal for the task, being
resistant to wind and rain, and safe from the ants that inhabit the
forest floor.
This behavior was first observed by Dr. William G. Eberhard at the
university of Costa Rica. His observations have led him to believe
that the mind control is most likely accomplished through a
fast-acting chemical secreted by the larvae, but what that chemical
is– and how it works– is a mystery. What he has found is that the
spider's usual five-step web building process is reduced to two
when held captive by these larvae, resulting in the alternate
design; and he has also discovered that if he removes the larvae on
the last day, just before the spider is killed, the spider will
often recover after a few days of spinning the abnormal web.
It is true that many parasites are able to shape their host's
behavior subtly, but never before has science observed a parasite
that can manipulate its host in such a detailed, specific way. As
evidenced by this finding, biology certainly has many fascinating
secrets yet to be discovered.
Scientific article from the Journal of Arachnology: Under the
Influence
http://www.damninteresting.com/?p=17
