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Attack of the Caterpillars

21 July 2005 (All day)
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Mmmm, lunch. A Hyposomocoma molluscivora caterpillar dines on a snail caught in its silk web.

Most caterpillars are docile vegetarians, content to while away their days munching leaves. But a new study has found a glaring exception to this rule: a Hawaiian caterpillar that ensnares snails in spiderlike webs of silk before devouring their flesh.

Hawaii is full of oddball insects. Scientists attribute this to the island's remoteness--it's the most isolated landmass on Earth. Some of the more bizarre finds include the oxymoronic flightless fly and the spearing spider that uses enlarged claws to impale prey. Now joining these ranks is the Hyposomocoma molluscivora, a snail-stalking caterpillar that reaches up to 10 millimeters in length.

Like other caterpillars, Hyposomocoma appeared to have some camouflage attached to its body. But these decorations were unusual: fragments of snail shells. So Daniel Rubinoff, an entomologist at the University of Hawaii at Manoa, took a few back to the lab. Oddly, the caterpillars shunned usual food. When the team tried to feed them carrots, the insects starved to death. Then the researchers thought about the shell attachments. When offered live snails, the caterpillars dug in. Rubinoff was incredulous: It was like "discovering a wolf diving for clams," he says.

And the oddities didn't end there. The caterpillars turned out to be talented hunters. The researchers observed them spinning webs of silk that trapped snails against leaves--a behavior not seen in any other caterpillar species. "I have hundreds of pictures because I just couldn't believe it," says Rubinoff, whose team reports its discovery 22 July in Science.

"I have been watching caterpillars for a long time, and this finding is quite novel," says Steven Montgomery, an entomologist in Hawaii who more than 2 decades ago reported the first predatory caterpillar--a species that fed on other insects. The next step will be studying Hyposomocoma's close relatives to see when and how these behaviors evolved, adds Rosemary Gillespie, an entomologist at the University of California, Berkeley.

Related sites
Rubinoff's home page
Photos of snail-feeding Hawaiian caterpillars
More caterpillar facts

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