Like many geographically-isolated locations, Hawai'i is an extraordinary evolutionary site that contains many unusual invertebrates. In 2025, a research article led by Daniel Rubinoff in the journal Science described an unusual caterpillar, referring to it as a ‘bone collector’ (Hyposmocoma sp.).
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The ‘bone collector’ caterpillar earned its moniker from its rather macabre home-decor tendencies. It lives in spider webs and constructs portable cocoons with inedible parts of the spider’s prey – potentially to camouflage itself against its ‘landlord’. An ant’s head here, or a fly wing there – a perfect home for the bone collector caterpillar.
The caterpillar is quite particular about its decorating, carefully measuring insect body parts for size, rotating, probing and chewing down the ones that don’t fit. It specifically uses corpses – researchers have found that when in captivity, these caterpillars do not accept other bits of organic matter, which suggests this decoration is crucial for their survival.
This carnivorous caterpillar is the only known caterpillar lineage to cohabitate with spiders. It crawls through the jumble of web and dead organic matter and eats any weakened or recently-killed insects it comes across. It’s also an adaptable predator and will even cannibalise its own kind if needed.
This is remarkable given that the Lepidoptera order is the most herbivorous of all insect orders: only 0.13 per cent of the nearly 200,000 moth and butterfly species are carnivores. A lot of these insect-eaters reside in Hawai'i, with 18 of the 20 native species there having evolved into predators.
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The ‘bone collector’ caterpillar has been recorded on the webs of at least four different species of spider, none of which are native to Hawai'i.
It belongs to the genus Hyposmocoma – one of Hawai'i’s oldest, at 14 million years old. The bone collector lineage itself is at least six million years old, making it three million years older than the island it now calls home, O’ahu.
This suggests that the bone collector lineage once occurred on older Hawai'ian islands, from which an ancestor moved to O’ahu.
Despite over a century of research, it’s only been found in a 15km2 area on O’ahu, and over two decades of fieldwork have yielded only 62 individuals.
“Without conservation attention, it is likely that 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,” explain the study’s authors.
Read the full findings here.
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Top image: after taking the bark of this rotting log, the scientists found a cobweb with a non-native spider and its eggsac, right next to a bone collector larva. The cobweb is covered in frass (excrement) from insects like beetles and termites that are eating the wood. Credit: Daniel Rubinoff
