A FLESH-EATING caterpillar that uses spider-like silk to trap snails before devouring them alive has been found in Hawaii.

Once the larvae, which develop into moths, have tied the snails to leaves, they climb inside their shells to feast on the soft tissue.

The caterpillar, which is native to the island of Maui, has been named Hyposmocoma molluscivora, in recognition of its status as the first known species to hunt molluscs.

Researchers have since discovered a second variety, which remains unclassified and unnamed but which adopts similar tactics, on another Hawaiian island, Molokai.

The two finds illustrate evolution in action, showing how the isolation of species can lead to behaviour that is rarely seen. The Hawaiian islands make up the world’s most remote land mass, and many of the creatures that have evolved there — particularly invertebrates such as insects — have adopted feeding strategies not observed elsewhere.

Other Hawaiian oddities include predatory caterpillars that ambush their prey, spiders that impale insects in mid-flight, and damselflies with nymphs that live on land and not in the water.

The new species of caterpillar was identified by Daniel Rubinoff and William Haines, of the University of Hawaii, who publish details of the discovery today in Science.

Caterpillars are the larval stage of insects from the order Lepidoptera, which include butterflies and moths. The majority of these insects are herbivores: an estimated 150,000 Lepidoptera species are known to science, and only about 200 are predators or parasites. All caterpillars have glands capable of producing silk — the silkworm is a kind of caterpillar that will eventually grow into a moth — but none has previously been found to use it in similar fashion to spiders. The Hyposmocoma molluscivora caterpillar is about 8mm (0.3in) in length and uses its sticky silk to build a case that serves as camouflage and protection.

When the caterpillar finds a snail of the genus Tornatellides — which is native only to Hawaii — it attaches sticky silk fibres to its shell. It anchors these silk bonds to the leaf on which the snail is resting, preventing its prey from moving.

Once the snail is immobilised, the caterpillar wedges its case next to the snail shell before stretching its body out of the case and into the shell. It then “pursues the retreating snail to the end of the shell from which there is no escape,” Dr Rubinoff said. “We observed 18 attacks by 10 different larvae following this sequence.”

STRANGE SPECIES

• At least 18 Eupithecia genus caterpillars are carnivorous and ambush prey, their tail looping back to seize it in one twelfth of a second
• Most damselfly young, called nymphs, are aquatic. Hawaii has a species whose nymphs live on land
• Many Hawaiian spider species have abandoned web-spinning, either seizing prey or, like Doryonychus raptor, impaling it in mid-flight

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