“We showed that the spider was quite happy
for more than a day.” — ROGER SE YMOUR

into streams and rivers with the help of plastrons, trapped films of air that coat their bodies. As the bugs consume this trapped oxygen, gas diffuses in from the surrounding water, replenishing the supply, says Morris Flynn, a mechanical engineer at the University of Alberta in Canada. In contrast, diving bell spiders seem to actively replenish their air bubble— called a diving bell after the antique submarines — by frequently traveling to the surface to grab more air. They trap a bubble between their back legs and abdomens, later adding it to the bell. This keeps the diving bell from collapsing.

The oxygen
coming
into the bell
may, at
times, match
a resting
spider’s
consumption.

But scientists didn’t know if the spiders’ diving bells, which the crawlers can leave behind while they go grab food or find a mate, were anything more than scuba tanks, holding a one-time supply of air.

It turns out that, like plastrons, the
diving bells behave like gills too, Roger
Seymour of the University of Adelaide
in Australia and Stefan Hetz from
Humboldt University of Berlin dis-
covered. At least five times the
original supply of oxygen can dif-
fuse into an occupied bell between
replenishment trips,
Seymour says. Using tiny
oxygen probes, the team
discovered that the oxy-
gen coming into the bell
may, at times, match a rest-
ing spider’s consumption.
By estimating the oxygen
needs of a spider resting in
an average-sized bell, “we
showed that the spider was
quite happy for more than a day,” says
Seymour. In fact, the bells’ endurance
seems to be largely limited by nitrogen
rather than oxygen, he adds. Nitrogen
gas slowly leaks out of the bubbles like
air from a balloon, leading to collapse.

Diving spiders may have to visit the surface more than daily, however, since they do more than rest. In this study, the team observed that before dining on insects captured in underwater webs — an energy-intensive feat — spiders paddled to the surface to squirrel away more air.

The diving bell’s gill-like properties
do, nevertheless, mean that spiders can
stay safely in their bubbles for longer.
The open water is a dangerous place
filled with predatory fish and insects,
which are generally better swimmers
than the spider, says Michael Taborsky,
a behavioral ecologist at the University
of Bern in Switzerland. “When they have
to go to the surface to replenish their
oxygen preserves,” Taborsky says, “this
is the dangerous side.”
Diving bells may have their limita-
tions, but insect plastrons could inspire
submersible designs, Flynn says. Some
researchers have already proposed con-
touring small underwater crafts so that
their fuel cells collect similar pockets of
air, providing the machines with a con-

S. HETZ, ADAPTED WITH PERMISSION FROM J. OF EXPERIMENTAL BIO.

Aquatic spiders
make bubbles
for breathing
Swimming arachnids can
extract oxygen from water

By Daniel Strain

In Germany’s Eider River, spiders not only swim with the fishes, they kind of breathe like them, too.

Eurasian diving bell spiders ( Argyro-neta aquatica) survive entirely underwater by living in large air bubbles, which the crawlers trap in silken webs. A new study shows that these bubbles work like a “physical gill,” drawing oxygen in from the water to match much of the spider’s consumption. Researchers from Australia and Germany report their findings in the July 1 Journal of Experimental Biology.