A newly discovered species of caterpillar has been found creeping through spider webs on the Hawaiian island of O‘ahu – and it’s unlike anything scientists have seen before.
Not only does it live in an eerily precarious environment, suspended among webs inside tree hollows, rock crevices and fallen logs, but this caterpillar is carnivorous. And after it’s finished feasting on its prey, it wears their body parts as camouflage.
Dubbed the ‘Bone Collector’ by the researchers who found it, this bizarre insect is a rare exception in the insect world. Out of around 200,000 known moth and butterfly species, just 0.1 per cent are carnivorous.
“Carnivory is exceptionally rare in caterpillars,” Prof Adam Hart, an ecologist, conservation scientist and entomologist at the University of Gloucestershire, who wasn’t involved in the study, told BBC Science Focus. “In fact, it’s only known from a group of species in Hawaii.”
This new species survives by scavenging: it feeds on weak or dead insects that get caught in spider webs, chewing through the silk if necessary to reach its meal.
As it drags its silk case (the outer layer that protects it before it turns into a moth) through the sticky threads, bits of exoskeleton and insect limbs accumulate, creating a macabre but effective disguise.
In total, the researchers identified body parts from more than six different insect species attached to these caterpillars. But this is no random collection – it’s artfully curated.
“The body parts are carefully measured for size before the caterpillar weaves them into its collection,” wrote the authors of the study, published in Science.
Parts are rotated for the best fit, and oversized pieces are chewed down to size before being stitched in. The result: a gruesome yet deliberate suit of armour made from the corpses of its prey.
“Many caterpillars have incredible camouflage, but this tends to be 'baked in' to the way they look and behave,” Hart said. “Using the environment as camouflage like this is unusual but not unheard of in moths. Bagworm moth caterpillars construct cases from environmental material in this way, for example.”
To learn more about the species, researchers raised some of the caterpillars in captivity. They quickly noticed another unsettling behaviour: cannibalism. Given that only one caterpillar is ever found per web in the wild, this might explain why they live alone.
They also tested whether the bone collectors would use other types of debris for decoration. They wouldn’t – only insect remains would do.
Despite its strange lifestyle, this species has been around a long time – possibly six million years, which is more than twice the age of the island of O‘ahu itself.
But its current range spans just 15km² (5.8 square miles) making it extremely vulnerable to extinction. Without urgent conservation efforts, the researchers warn, “the last living representative of this lineage of carnivorous, body part-collecting caterpillars that has adapted to a precarious existence among spider webs will disappear.”
“There are a lot of weird and wonderful invertebrates out there – and many more left to discover,” Hart said. “But a moth caterpillar disguising itself with the remains of insect prey and living a predatory life in a spider's web? Yes, that is certainly up there with the weirdest – and the most wonderful – I've heard of for some time.”
About our expert
Adam Hart is an entomologist and professor of science communication at the University of Gloucestershire. As well as research and teaching, he is a regular broadcaster for BBC Radio 4 and the BBC World Service, presenting documentaries on topics from trophy hunting to tree diseases. He has also presented the weekly science program Science in Action for the BBC World Service. On television, Adam has co-presented several documentary series, most notably BBC Four’s Planet Ant and BBC Two’s Hive Alive.
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