UH researcher documents the unique behavior of Hawaiian predatory caterpillar

Caterpillar's meal of choice is snails

University of Hawaiʻi at Mānoa
Daniel Rubinoff, (808) 956-8432
Department of Plant and Environmental Sciences
Miles Hakoda, (808) 956-3093
College of Tropical Agriculture and Human Resources
Posted: Jul 21, 2005

HONOLULU — In a recently published work in Science, UH assistant professor Daniel Rubinoff in conjunction with his graduate student William P. Haines described the unique behavior of predatory caterpillars in the genus Hyposmocoma. The newly discovered caterpillar species are native to Hawaiʻi and are unique because they feed on snails and use a silk-spinning technique to capture their prey.

"Snails and caterpillars co-occur in habitats throughout the world. What makes this situation interesting is that only Hawaiʻi caterpillars have evolved to eat snails," said Rubinoff. "Perhaps the question is what‘s so special about Hawaiʻi? But we could also ask, what‘s different about the rest of the world? Snails and caterpillars co-occur on all mainland areas except Antarctica. The difference might be the presence of native snails and caterpillars in the absence of other predators or competitors. Ultimately a mix of factors in the local environment might be responsible for the change."

Caterpillars are the immature stage of Lepidoptera, butterflies and moths, one of the three most diverse orders of insects. Lepidoptera, consist overwhelmingly of plant-eaters — of 150,000 species known worldwide, but only about 200 or 0.13 percent are known to be predators or parasites. Of these predatory caterpillars, almost all feed on soft-bodied insects or ant brood. None have been previously recorded feeding in the Phylum that includes snails, suggesting a very big evolutionary change in food choice.

The caterpillars inhabit predominantly native wet and rain forests in the Hawaiian Islands and maintain a strict diet of native snails. They are very specific eaters and will not accept foliage, even if starving. Because the snail‘s shell presents a challenge, the caterpillar has learned to utilize its silk in a spider-like fashion to immobilize its prey. Although all caterpillars have the ability to produce silk to form cocoons, this is the first record of a predatory caterpillar which uses silk to catch live prey.

Upon capturing and binding a snail to the leaf on which it was resting, the caterpillar strategically wedges its cocoon next to or inside the snail shell. It then stretches out from the cocoon to attack and consume the snail, pursuing it to the end of its shell.

The nature preserves where these snail-eating caterpillars exist contain some of the last vestiges of native forests in Hawaiʻi. The resulting moth from the caterpillar is a member of Hyposmocoma a (endemic-found nowhere else) Hawaiian genus of small moths containing at least 350 recognized species.

"Further studies may contribute additional knowledge to what constrains or facilitates evolutionary development in this species, which may lead to more ideas about how evolution functions in general," said Rubinoff. "It is imperative that the remaining natural habitat be preserved to protect this and other, as yet undiscovered, evolutionary novelties that are uniquely Hawaiian."

About the College of Tropical Agriculture and Human Resources (CTAHR)

The College of Tropical Agriculture and Human Resources is the founding college of the University of Hawaiʻi. CTAHR is an integral part of the University of Hawaiʻi at Manoa's Carnegie I Research Institution designation and is the Land Grant college of the University of Hawaiʻi. CTAHR is federally mandated to fulfill the University's threefold Land Grant mission of instruction, scientific research, and outreach to address State needs. No other college at the UH has such an extensive mandate or interacts so closely with the citizens of the State.

About the University of Hawaiʻi (UH)

Established in 1907 and fully accredited by the Western Association of Schools and Colleges, the University of Hawaiʻi is the state‘s sole public system of higher education. The UH System provides an array of undergraduate, graduate, and professional degrees and community programs on 10 campuses and through educational, training, and research centers across the state. UH enrolls more than 50,000 students from Hawaiʻi, the U.S. mainland, and around the world. For more information, visit www.hawaii.edu.