for National Geographic News
Water spiders survive below the surface thanks to a rudimentary "scuba tank" they spin from their own silk, a new study says.
Scientists at the University of Bern, Switzerland, determined that spiders use these scuba tanks, called air bells, as reservoirs, monitoring and replenishing oxygen levels to enable the animals to live underwater.
"The water spider's air bell is in some ways working like an external lung," said study co-author Michael Taborsky.
Found in ponds throughout northern and central Europe, the water spider is the only spider that spends its entire life underwater.
Since the small brown arachnids are air breathers, they have adapted the air bell system to gather oxygen from the atmosphere. (See spiders spinning their deadly silk.)
Living in a Bubble
The air bell serves multiple purposes, said Paul Selden, a professor of invertebrate paleontology at the University of Kansas who was not involved in the study.
"[The water spider] uses this air bell as a place to live away from terrestrial predators and as a safe nest in which to keep her eggs and tend the young spiderlings," Selden said.
It is also used as a safe harbor for consuming prey and breeding.
Using short hairs on their abdomens and legs, water spiders trap air bubbles from the water's surface, which they then carry back to specially designed underwater reservoirs spun from silk, the recent study found. (Related: "Gene for Key Spider-Silk Protein Found" [August 2, 2005].)
As the spider fills the web structure with air, the structure takes on a bell shape and a silvery sheen. The silk membrane allows oxygen to diffuse in from the water and carbon dioxide to diffuse out, so the spiders do not have to replenish the air supply often.
But until this recent study, scientists did not know that the water spiders also used the air bells to breathe.
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