In the misty mountain forests of Oahu, Hawaii, lives a caterpillar that takes decoration to a macabre extreme: instead of gluing leaves and pebbles to its protective silk case, it adorns itself with the body parts of its prey—fly wings, weevil heads, earwig abdomens. Scientists call it the Bone Collector.
The discovery was published in *Science* in April 2025. First author Daniel Rubinoff, an entomology professor at the University of Hawaii at Manoa, and his team spent more than 20 years finding just 62 individuals.
Three Conventions Broken
1. It eats meat. Of the roughly 180,000 known butterflies and moths, nearly all caterpillars are herbivores. Carnivorous caterpillars are an extreme minority in Lepidoptera.
2. It lives in spider webs. The Bone Collector doesn't hunt. It lives inside spiders' webs and secretly feeds on trapped prey—a textbook case of kleptoparasitism (food theft), comparable to frigatebirds stealing fish from other seabirds, except here the size gap between thief and host is enormous.
3. It wears its victims. Like all *Hyposmocoma* caterpillars, it carries a silk case. But while relatives decorate with lichen, sand, or algae, the Bone Collector selectively attaches prey body parts with silk. Researchers observed the caterpillars seemingly "measuring" fragments before attaching them. The camouflage likely makes it blend into the debris-strewn web—looking like just another pile of insect remains—right under the spider's eyes.
One Genus, 400 Species, Explosive Radiation
The Bone Collector belongs to *Hyposmocoma*, a moth genus found nowhere but the Hawaiian islands, with over 400 species (about 350 formally described, likely many more unnamed). For comparison, Darwin's Galápagos finches number about a dozen; Hawaii's famous fruit fly radiation around 500 species.
Descended from an ancestor that arrived roughly 6 million years ago—older than Oahu itself (3–4 million years)—the genus has diversified into caterpillars that:
- Eat leaves, dead wood, seeds, and ferns
- Prey on snails (*Hyposmocoma molluscivora* lassoes live snails with silk)
- Live amphibiously, feeding and breathing underwater
- Steal food from spider webs
Landlord and Tenant
The spider, of course, can sense vibrations in its web and distinguish struggling prey from a drifting leaf. The Bone Collector must avoid producing prey-like vibrations and avoid looking like a threat. Its corpse-camouflage solves the latter; researchers speculate it may hide its movements within the web's background "noise" of wind and struggling insects.
Why doesn't the spider evict this freeloading tenant? Possibly it can't detect the caterpillar—or the cost of expulsion outweighs the small amount of food lost. The relationship slides along a spectrum between commensalism and parasitism depending on how much is stolen.
62 Individuals in 20 Years
The Bone Collector survives only in a small patch of Oahu's mountain forest, threatened by invasive ants, plants, and snails. Hawaii is called "the extinction capital of the world"—over a third of US federally listed endangered species are from Hawaii, and most *Hyposmocoma* species have never even been assessed.
As Rubinoff said upon publication: "We really need to better protect these species."
A 6-million-year evolutionary history, a 400-species radiation, snail-eaters, amphibious caterpillars, web-dwelling thieves—all of it could largely vanish within our lifetimes. And most people never knew it existed.
Postscript: On Camouflage
Perhaps the Bone Collector's disguise isn't about deceiving others so much as finding a way to move safely through a dangerous world. It doesn't need to *be* a corpse—only to look like one. That may be why it has survived 6 million years in spider webs: not because it's the strongest, but because it found a way to live without needing to be.
Sometimes the best armor isn't a hard shell—it's camouflage that makes others think you're not worth attacking.
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*Source: Rubinoff et al., published in Science, April 2025. Original Chinese forum post from zhichai.net.*