Non-stick spiders take delicate steps
17 Mar,BBC
Orb-weaving spiders avoid sticking to their own webs because of the
way they move, say scientists.
Naturalists first investigated the puzzle of how spiders move around
their webs a century ago.
The spiders' non-stick abilities were originally attributed to a
special coating on their legs.
But researchers in Costa Rica have now used modern imaging technology
to record close-up footage that fully explains the ability.
Dr William Eberhard and Dr Daniel Briceno published their findings in
the journal Naturwissenschaften.
"Orb-weaving spiders are abundant in many parts of the world, and
their ability to build and utilise adhesive traps without becoming
entangled themselves has been a source of puzzlement for more than 100
years," Dr Eberhard said. Observations in the early 1900s suggested that
the spiders coated their legs with an oil from their mouth but without a
close-up examination, this remained a theory.
More recent studies found that spiders "tip-toed" around their webs
on fine hairs to avoid too much contact with the sticky surface.
However, during web construction the spiders are known to forcefully
thrust their legs on to the threads but still, somehow, they do not
stick.
To solve this puzzle, Dr Eberhard and the team combined a video
camera and a microscope to record the spiders in minute detail.
They identified three factors that combined to stop the spiders from
sticking: leg hairs that decreased the surface area available to stick;
a chemical coating on the hairs that reduced the adhesion and the
delicate way the spiders move their legs. "Spiders reduce their adhesion
to the sticky lines in their webs by moving their legs carefully so as
to allow the sticky lines to slide off easily," Dr Eberhard told BBC
Nature.
Under the microscope, the researchers saw that when a spider made
contact with a sticky line the adhesive droplets were transferred to its
leg hairs. Then, as the spider withdrew its leg from the web, the
droplets slid down these non-stick hairs and dripped off the fine point
at the end.
The scientists compared this "drip tip" to the way water easily runs
off the pointed leaves of tropical plants. |