Friday, July 22, 2005

ENV: New silk-producing snail predators

as if the increasingly endangered snails of Hawaii needed any more enemies . . . at least this one has evolved along with them . . .

Hawaiian caterpillars hunt like spiders
Insect uses a surprising silk-spinning strategy to trap snails
Reuters, Updated: 3:25 p.m. ET July 21, 2005

WASHINGTON - Tiny, snail-eating caterpillars found in Hawaiian rain forests tie up their prey with sticky silk and snack on them at leisure, surprised scientists say.

It is the first time that caterpillars that eat snails or any other mollusk have been found, the researchers write in Friday's issue of the journal Science.

And while caterpillars of all kinds spin silk to make cocoons, this is the first time one has been seen to use it as spiders do to capture prey.

"Although all caterpillars have silk glands, this predatory caterpillar uses silk in a spiderlike fashion to capture and immobilize prey," Daniel Rubinoff and William Haines at University of Hawaii wrote in their report.

The caterpillars of the newly described species, Hyposmocoma molluscivora, are small — about a third of an inch (8 millimeters) long. Wrapped in their cocoons, they "lumber along" leaves, Rubinoff and Haines said.

"The caterpillars do not eat plant foliage, even when starving," they wrote.

Instead, they hunt Tornatellides snails.

When they find one, "they immediately begin to spin silk webbing attaching the snail shell to the leaf on which it rests, apparently to prevent the snail from sealing itself against the leaf or dropping to the ground," the researchers wrote.

"The larva (caterpillar) then wedges its case next to or inside the snail shell and stretches much of its body out of its silk case, pursuing the retreating snail to the end of the shell from which there is no escape. We observed 18 attacks by 10 different larvae following this sequence."

Sometimes the caterpillars decorate their silk casings with empty snail shells, probably as a form of camouflage, the researchers said.

The caterpillars eventually become small moths.

The researchers say they are surprised by the findings and note that the caterpillars join a range of unusual Hawaiian fauna, including spiders that impale their prey in flight.

"Caterpillars and terrestrial snails co-occur widely on all the continents where they are present, but only in Hawaii have caterpillars evolved to hunt snails," they wrote.


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