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Bottled crab. Hermit crabs have no qualms about crafting a home from human trash.

Litter-Loving Crabs

The vast quantities of trash unleashed upon the seas usually harm the denizens of the deep. But hermit crabs may be taking advantage of some garbage, new research suggests. The crabs are climbing up the mobile property ladder by way of broken bottlenecks, plastic containers, and other trash.

Hermit crabs typically reside in secondhand mollusk shells collected from dead or living gastropods. They obtain their mobile homes in bizarre swap meets with other unsatisfied hermit crab homeowners, dig them up from the sea floor, or even fix up ancient fossil shells. Still, suitable shells are often in short supply--and human activities have added to crab housing shortages by hurting some mollusk populations.

Ironically, human trash might help fill the gap, says ecophysiologist David Barnes of the British Antarctic Survey in Cambridge, U.K. The quantity of ocean-borne trash--mostly plastic--is rising, he notes, and some of the refuse has become prized real estate.

Hermit crabs all over the Pacific and Indian oceans, from heavily developed Asian coastlines to remote islands, are starting to make homes in plastics and glass, Barnes reports in the December issue of Biologist. "Suitably shaped persistent rubbish, like bottle tops, could yet become one of the most plentiful sources of housing," he predicts.

That doesn't surprise Brian Hazlett, who studies animal behavior at the University of Michigan, Ann Arbor. When faced with a housing crunch, he says, "hermit crabs use what they can, even human junk." Ecologist Tim Benton of the University of Stirling in Scotland wonders what the evolutionary significance of such a trend might be. "Plastic is a heck of a lot lighter" than a large mollusk shell, says Benton, and crabs that adopt lighter shells might be at an advantage if they're quicker on their feet.

Related sites
Hermit crab biology from the Museum Victoria in Melbourne, Australia
The British Antarctic Survey