The snail feeding habits of Hyposmocoma molluscivora were discovered when a student found the snail-eating caterpillars on the Hawaiian island of Maui and brought them to entomologist, Daniel Rubinoff. No previous caterpillar had ever been known to feed on snails. Therefore, Rubinoff thought the student must be mistaken and first tried other foods on the caterpillars. Caterpillars did very poorly until snails were placed in the container with the caterpillars.
Hyposmocoma molluscivora caterpillars will not attack moving snails. The caterpillars wait until they contact a snail that has stopped moving. Then the caterpillars vigorously spin silk threads to tie the snail to a plant leaf and immobilize the snail. At this point the snail cannot escape. The caterpillar enters the snail shell through the opening and feeds on the snail inside its shell. Sometimes the caterpillars will attach an empty snail shell to the silk case that the caterpillars weave around their body. The snail shell may provide protection against other predators.
Remote islands such as Hawaii have many unique species. A species that finds itself on an island, may be able to exploit common resources without much competition. This appears to have occurred with the genus Hyposmocoma which has many unusual species.
Daniel Rubinoff and William Haines. Science 22 July 2005:
Vol. 309 no. 5734 p. 575