The ‘bone collector’ caterpillar wears its prey as camouflage

A severed ant head. A fly wing. A beetle abdomen. These body parts ripped from dead insects adorn a caterpillar’s protective coat. That’s why scientists are calling this newfound species the “bone collector.”

This caterpillar sports remains of prey as camouflage while it searches spider webs for trapped bugs. The meat-eating caterpillar was found on the Hawaiian island of Oahu. It is the first known by scientists not only to live in spider hunting grounds but also to fully decorate itself with body parts.

Researchers described the caterpillar April 25 in Science.

Relatively few caterpillars eat meat. Of nearly 200,000 known moth and butterfly species, only about 300 types are carnivorous. The bone collector caterpillar belongs to the moth genus Hyposmocoma. They are native to the Hawaiian Islands. All members wear protective coats when young. They’ve come to be known as Hawaii’s fancy-case caterpillars.

A meat-eating caterpillar on the Hawaiian island of Oahu adorns itself with body parts from its prey. This macabre coat helps it hide from spiders, whose webs make up the caterpillars’ hunting grounds. Known as bone collector caterpillars, these insects are also cannibals. This short, double-speed video shows it eating another of its species.

While walking in the Waianae Mountains almost 20 years ago, some scientists spied an odd caterpillar next to a spider web in a tree hole. “It [was] covered in little bits of bug,” recalls Dan Rubinoff. He works for the University of Hawaii at Mānoa in Honolulu. As an entomologist, he studies insects.

At first, he had dismissed that caterpillar as a curiosity. But over time, he kept crossing paths with more weird caterpillars. Over the next two decades, he and others spotted 62 of these bone-collector caterpillars. All were within a 15-square-kilometer (almost 6-square-mile) range.

Each lived in a spider web tucked away in a tree, log or rock cavity. And there was never more than one per web (otherwise one would eat the other). The caterpillar lurks in a web, waiting to prey on insects stuck there. The caterpillar masks its scent and texture with leftovers from prey on which the spider had dined. The caterpillar even wears skin shed by its eight-legged landlord.

This bone collector caterpillar case is decorated with body parts from at least six different families of insects (some labeled). Unlabeled pieces are skin shed by a host web’s spider.Rubinoff lab/Entomology Section/University of Hawaii at Mānoa

“This is a decorate-or-die situation,” Rubinoff explains. A plain protective case “might not be enough to stop the spider from trying to puncture the case and eat the caterpillar.” 

When assembling its prey-based wardrobe, a caterpillar carefully probes and rotates those bodily remains. The carnivorous critter first nibbles large pieces down to size. Then, it weaves them onto its silken case. After a few months of feasting, the caterpillar seals off the open end of its case. Now, that case will become its cocoon as the caterpillar transforms into a moth.

Scientists analyzed the bone collector moth’s genes. They found that its lineage is at least 6 million years old. That’s even older than the island of Oahu! So this critter’s ancestors may have originated on a different island. Other Hyposmocoma moths are represented by multiple species on several of the Hawaiian Islands. But the bone collector is the only species in its line, Rubinoff says.

And, he adds: “I’m really glad we discovered it before it went extinct.”