For longer versions of these and other
Life stories, visit www.sciencenews.org
Tarantulas shoot silk from their feet
By Susan Milius
Comic books may have gotten
their science right after all.
Some spiders may indeed grip
walls by shooting silk Spiderman–style from their limbs.
New experiments support
the idea that tarantulas can
shoot silk from their feet to
grip a slippery surface. The
notion had been dismissed,
but researchers say they have
spotted silk footprints left
behind by spiders in precarious positions. What’s more,
electron microscopy reveals hairlike projections on tarantula feet that
could be silk extruders, Claire Rind and
colleagues at Newcastle University in
England report in the June 1 Journal of
Experimental Biology.
“The controversy over [foot] silk is
important for understanding the evolution of silk production in spiders,”
says evolutionary biochemist Todd
Blackledge of the University of Akron
in Ohio. Spiders are “preeminent silk
craftsmen,” he says. Many create multiple silks with different functions, made
from complex structures called spinnerets with arrays of spigots and their
own musculature.
When a 2006 Nature paper contended
that zebra tarantulas had some kind of
previously unnoticed silk glands in their
feet, the possibility “made quite a splash
in the arachnological community,”
Blackledge recalls. “It seemed almost
too good to be true that morphologists
working on tarantulas hadn’t already
described this.”
Maybe it was too good to be true,
Fernando Pérez-Miles of Universidad
de la República in Montevideo, Uruguay,
reported in 2009. He and his colleagues
lined tarantula containers with small
New research reopens debate over whether some
spiders, such as this Mexican flame-kneed taran-
tula named Fluffy, can shoot silk from their feet.
pieces of glass. Checking the glass with
a microscope revealed wisps of silk on
the vertical surfaces, but only when the
tarantulas were free to use their abdominal spinnerets. When the researchers
Hey Kitty, dogs
do drink like cats
Canines toss water into their
mouths just like feline rivals
By Susan Milius
There may be some outraged sofa clawing and houseplant destruction over this,
but a complex system of lapping liquids
described last year for cats turns out to
be the way dogs drink too.
High-speed video using X-rays now
shows that dogs get water into their
mouths by relying on the way liquid
adheres to their tongues and the inertia of fluid columns, says evolutionary
biologist A.W. Crompton of Harvard
University. Dogs plunge their tongues
into liquid and, like cats, swiftly pull up
a little column of it through adhesion.
Before gravity overcomes the column’s
put wax on the tarantulas’ abdomens to
block the spinnerets, silk didn’t show up
on the vertical slides.
Rind, however, wasn’t satisfied. The
study hadn’t forced the spiders into challenging climbs that might require foot
silk. Also, Rind suspected that tarantulas in particular would benefit from
silk-making feet as a way to prevent falls,
which can crack their large bodies open.
To give the idea another test, Rind
lined cages with glass slides. She and
her colleagues videotaped three species
of tarantula as their cages were tilted
so the spiders were clinging vertically
and then given a little shake. Where the
videos showed a foot slipping a bit, Rind
found tiny wisps of silk.
Rind did not wax the abdominal spinnerets closed, which Pérez-Miles says
would have helped to convince him that
the silk indeed came from the feet. Rind
says the videos pinpointed foot location
well enough to justify skipping the wax
job, which ultimately kills the spiders.
inertia and the liquid splashes down
into the bowl again, the dogs snatch a
sip, Crompton and Catherine Musinsky,
also of Harvard, report online May 25 in
Biology Letters.
That’s basically the same mechanism
a team reported admiringly in Science
last year when describing the way cats
lap liquids (SN: 12/4/10, p. 5).
“We surely were surprised when we first
saw their results,” says Roman Stocker of
MIT, a coauthor of the cat study.
Crompton and Musinsky’s X-rays also
add a new chapter to the story of lapping by detailing how liquid gets from
the front of the tongue to the swallowing point. The tongue traps the water
against the ridged roof of the mouth. As
the tongue moves in and out again and
again for subsequent laps, captured bits
of liquid travel back. A particular bit of
captured liquid may need three tongue
extensions to get swallowed. Cats probably do this too, Crompton says.
F.C. RIND
www.sciencenews.org
