It sounds like a setup for a horror movie: a meat-eating, cannibalistic caterpillar hiding in the shadows of a spiderweb and dressed in the remains of its former prey. But this incredible species, dubbed the “bone collector” and previously unknown to biologists, is real and living in a small section of forest on the Hawai’ian island of O’ahu.

For the research team from the University of Hawai’i at Mānoa, this extremely rare discovery was 20 years in the making and shocked everyone involved.

“It’s not just unexpected, it’s unimaginable,” says Dan Rubinoff. “This caterpillar was not on anybody’s radar. We came up with so many alternative explanations for what was happening.”

The Bone Collector

This new caterpillar species is part of the genus Hyposmocoma, an ancient and diverse group only found in Hawai’i. This species in particular is estimated to be at least six million years old and is extremely rare, with only 62 observed in the field over the past 20 years. 

The study, published in Science, explains how everything about the bone collector is unique and surprising. They are predatory, opportunistic scavengers that dine on insects caught and weakened in spiderwebs, even sometimes stealing and eating the spider’s stored food. If they are unable to subsist on other insects, the caterpillar will resort to cannibalizing one of its own. 

The bone collector name comes from the fact that the caterpillars cover themselves and their silk casing in inedible insect parts. These inedible parts are either collected leftovers from their latest meal or pieces from spiders who formerly called their shared web home, a process Rubinoff describes as “decorate or die.”

The macabre camouflage is partially responsible for why researchers have taken 20 years to announce this discovery. In the beginning, they believed it was a coincidence that these caterpillars were covered in bug bits, assuming it was just a hazard of living in the spiderwebs. However, after years of observation, the team became confident that this behavior was not accidental and that they had in fact discovered a new species. 

Read More: How These 5 Tiny Caterpillars Protect Themselves With Deadly Venom

A Unique Caterpillar Relationship

It isn’t often that you see spiders and caterpillars cohabitating. Caterpillars are often at the very bottom of the food chain, so it’s very unusual to find a species that isn’t. 

Thanks to their camouflage ability, they effectively hide from the spiders they live with. And although their costume of discarded insect pieces catches our eye, it’s working on other senses, like smell and taste, for their spider neighbors.

If the spider happens to detect the caterpillar, the spider will come out and investigate. But when it does, all it can taste or smell is its inedible leftovers rather than the yummy caterpillar inside. 

The bone collector’s habitat also helps it effectively hide from human sight. 

“The way I describe the habitat is ‘places you wouldn’t want to reach your hand into.’ Like a tree hole, a rotted log, or under a rock. They are dark places,” says Rubinoff.

An Endangered Species

Currently, the bone collector caterpillars survive only in a small, 15-square-kilometer patch of mountain forest. And like many other native Hawai’ian species, they are at risk of extinction. Like for many other insects in Hawai’i, the replacement of native plants with invasive plants is primarily to blame.

Without conservation efforts, this newly discovered yet ancient species of caterpillar may disappear before we have the chance to learn from it. Although conservation is often a large-scale undertaking, there are things that can be done by the average person. If you are planning a trip to Hawai’i, you can ask about the flora and fauna that you see, as well as make sure to tour areas with native plants and forests. 

Carnivorous caterpillars are extremely rare, making up only 0.1 percent of the nearly 200,000 known moth and butterfly species. Caterpillars are often exclusively herbivores, which makes finds like the bone collector even more remarkable and protecting them even more important.

By studying this species, researchers can learn how caterpillars evolve to become meat eaters and why this may be such a difficult process. Having a living species of carnivorous caterpillars allows scientists to do genetic testing and find out what evolutionary changes are necessary for this unique behavior.

Genetic testing is exactly what Rubinoff and his team are hoping to do in the future, and not just to identify the bone collector’s unique genetic makeup. There are practical applications that can come from learning more about this new species, such as how caterpillars detect their food and recognize whether something is edible or wearable. Knowing more about food detection can help us develop less toxic ways of spraying crops that are still effective at preventing caterpillars from eating them.

Read More: How Counting Caterpillars Can Help Scientists Understand Climate Change

Article Sources

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As the marketing coordinator at Discover Magazine, Stephanie Edwards interacts with readers across Discover’s social media channels and writes digital content. Offline, she is a contract lecturer in English & Cultural Studies at Lakehead University, teaching courses on everything from professional communication to Taylor Swift, and received her graduate degrees in the same department from McMaster University. You can find more of her science writing in Lab Manager and her short fiction in anthologies and literary magazine across the horror genre.