You probably did this as a kid: collecting pretty leaves and pebbles and gluing them to your "secret base." Collecting and decorating is instinctive for human children.
But in a montane cloud forest on Oahu, Hawaii, one caterpillar has taken this to an extreme—it collects not leaves and stones, but fly wings, weevil heads, and earwig abdomens, gluing these body fragments one by one onto its silk case until it looks like a pile of insect debris.
Scientists call it the Bone Collector.
In April 2025, the discovery was published in *Science*. Lead author Daniel Rubinoff, an entomology professor at the University of Hawaii at Manoa, and his team spent more than 20 years finding a total of just 62 individuals.
62 specimens. 20 years.
This caterpillar isn't just rare—it's disturbingly rare.
One Caterpillar, Three Counter-Intuitive Traits
First: caterpillars that eat meat. Of the roughly 180,000 known butterfly and moth species, nearly all larvae are herbivores, feeding on leaves, petals, fruits, and roots. A few outliers exist—some inchworm larvae eat aphids—but carnivory is an extreme minority in Lepidoptera.
Second: it lives in spider webs. The Bone Collector doesn't live on leaves or branches. It lives inside the webs spiders build, sneaking bites from trapped prey when the spider isn't looking.
This behavior has an ecological name: kleptoparasitism—literally "thieving parasitism." Frigatebirds steal fish from other seabirds; skuas rob penguins. But a caterpillar stealing a spider's food? The size gap is like you living in a giant's house and sneaking leftovers from the fridge while the giant sleeps.
Third: it wears its prey's corpses. The Bone Collector belongs to the genus *Hyposmocoma*, whose caterpillars all spin protective silk cases they carry with them. Most *Hyposmocoma* caterpillars decorate their cases with lichens, sand grains, or algae to look like twigs or stones.
But the Bone Collector glues on prey body parts instead.
Researchers observed these caterpillars "measuring" prey parts—a fly wing, a weevil head—then precisely fastening them to their cases with silk. This isn't random accumulation but selective decoration.
Why? Camouflage, scientists believe. Spider webs are naturally littered with insect debris—wings, legs, shell fragments. By dressing itself as just another pile of debris, the caterpillar becomes invisible to the spider.
You wear fragments of corpses, pretending to be a corpse yourself—while eating the predator's food right under its eyes. It's a strategy as ruthless as a crime film.
One Genus, 400 Species: An Explosive Radiation
The Bone Collector belongs to *Hyposmocoma*, a moth genus found nowhere else on Earth except the Hawaiian Islands—with over 400 species, about 350 formally described, and likely at least as many yet unnamed.
For comparison, Darwin's Galápagos finches number only about a dozen-odd species. Hawaii's classic fruit fly radiation—cited endlessly in textbooks—has roughly 500 species. *Hyposmocoma*'s diversity rivals the fruit flies, yet it remains far less famous.
The genus's caterpillars do almost everything imaginable:
- Some eat leaves, living ordinary caterpillar lives
- Some eat dead wood, burrowing through rotting trunks
- Some eat seeds; some eat ferns
- Some eat snails—*Hyposmocoma molluscivora* lassos live snails with silk and eats them like corn on the cob
- Some are genuinely amphibious insects, able to breathe and feed underwater, then climb ashore and return
Six million years—older than the current island of Oahu itself, which is only 3–4 million years old. This means the Bone Collector's ancestors likely lived on older islands, "island-hopping" to new ones as geology shifted and old islands sank.
On an isolated archipelago with no predators and (initially) no competitors, one species can split into hundreds, each occupying a tiny ecological niche. Some became vegetarians, some hunters, some amphibious, some thieves living in others' webs.
It's a textbook case of adaptive radiation—yet textbooks rarely mention it.
Landlord and Tenant: A Delicate Relationship
The relationship with spiders is subtler than simple theft.
Spiders aren't fools. They sense vibrations in their webs and can distinguish a struggling fly from a wind-blown leaf. To operate under the spider's nose, the caterpillar must avoid producing prey-like vibration signals and avoid looking like a threat worth attacking.
The corpse-fragment camouflage likely solves the second problem: when the spider sees debris moving, it may not register a living caterpillar.
The first problem is trickier. Moving, feeding, even molting all generate vibrations. Researchers speculate the caterpillar may hide within the web's own "noise"—wind, rain, other prey struggling.
Why doesn't the spider evict this freeloading tenant? Perhaps it simply can't detect the caterpillar. Or even if it could, the cost of eviction may exceed the benefit of tolerance—the food stolen is negligible, and a spider web is already an open ecosystem hosting various tiny arthropods.
This resembles a modern analogy: "parasitic growth" in the internet business world—you don't build your own platform; you live on someone else's platform, using their infrastructure and siphoning their traffic. The Bone Collector is nature's original "platform parasite." The spider is the landlord; the caterpillar the tenant—using the landlord's infrastructure and resources while relying on camouflage to avoid detection.
Technically, this can be commensalism—one benefits, the other is unaffected. But if the stolen food is significant, it becomes parasitism. If the spider finally eats the caterpillar, the parasite becomes prey. Ecological relationships are never black and white; every relationship exists on a spectrum, sliding with changing conditions.
62 Specimens, 20 Years—and Then What?
Rubinoff's team spent 20+ years searching Oahu's montane forests, confirming only 62 Bone Collectors.
That number is unsettling.
The species lives only in a small patch of mountain forest on Oahu—a forest threatened by invasive ants, plants, and snails. Hawaii's ecosystems are among Earth's most fragile, because island species lost their defenses against competitors during long isolation.
The Bone Collector's lineage traces back 6 million years—older than the island it inhabits. It survived island formation and sinking, ice-age sea level changes, countless volcanic eruptions. But it may not survive the next hundred years.
When the paper was published, Rubinoff said: "We really need to do better to protect these species."
It's not a polite platitude. Hawaii is called "the extinction capital of the world"—more than a third of the endangered species on the US federal list come from Hawaii. Of *Hyposmocoma*'s 400+ species, the vast majority have never been assessed for conservation status.
The Bone Collector wears fragments of corpses, pretending to be one itself. But this time, camouflage may not be enough. It faces not a spider's vision but something it cannot disguise: habitat loss.
Six million years of evolution, a radiation of 400 species—snail-eaters, aquatic dwellers, spider-web squatters—may largely vanish within our lifetimes.
And most people will never even know they existed.
Postscript: On Camouflage
Writing this, I kept returning to one question: is the Bone Collector's camouflage meant to fool the spider—or itself?
It glues prey parts onto its case, looking like debris. But the case is its own making, and it knows it isn't debris. It knows it is moving, feeding, growing. It knows a living self lives inside the case.
Perhaps camouflage was never about deceiving others—it's about finding a way to move safely through a dangerous world. You don't need to become something else; you only need others to believe you are something else.
The Bone Collector doesn't need to become a corpse. It only needs to look like one.
That's probably why it has survived 6 million years in spider webs—not because it's the strongest, but because it found a way to live that never required strength.
Sometimes the best armor isn't a hard shell, but a disguise that makes others decide you're not worth attacking.