In a remarkable scientific breakthrough, researchers from the University of Hawaiʻi at Mānoa have uncovered a highly unusual and ancient caterpillar species in the forests of Oʻahu. Dubbed the “bone collector,” this caterpillar is unlike any other, donning insect remains as camouflage and making its home in spider webs—where it preys on unsuspecting insects caught in the arachnids’ traps. The discovery, recently detailed in the journal Science, marks the only known species of its kind in the world and provides rare insight into how evolution can defy conventional expectations.
Caterpillars typically belong to a vegetarian order of insects known as Lepidoptera, with fewer than 0.13% exhibiting carnivorous behavior. This makes the bone collector an exceptional outlier. As part of the genus Hyposmocoma, the species constructs mobile silk cases, but with a dark twist: it decorates them with discarded insect parts and spider remains. These “bone” suits not only help the caterpillar blend into its surroundings but also seem to protect it from being detected—or eaten—by its spider cohabitants.
Lead researcher Daniel Rubinoff, who has studied Hawaiian insects for decades, noted the evolutionary oddity of the species. “It’s like they’re hiding in the lion’s den—living inside a spider web and stealing food,” Rubinoff explained. “Evolution doesn’t follow our expectations.”
An Ancient Lineage on the Brink
Despite its fascinating biology, the bone collector caterpillar faces a grim future. Rubinoff’s team has identified its entire population within a narrow 16-kilometer stretch of forest in the Waiʻanae mountain range on Oʻahu. Genetic studies suggest that the lineage of this caterpillar predates the very island it currently inhabits, dating back over six million years. That means its ancestors likely lived on now-submerged or eroded Hawaiian islands before migrating to Oʻahu.
This extremely limited habitat makes the species highly vulnerable. While the caterpillars have shown the ability to coexist with invasive spider species, their ability to adapt may not be enough. Habitat loss due to deforestation, urban expansion, and the spread of non-native plants and animals has created a biological environment hostile to native Hawaiian species. Rubinoff likens the current state of Hawaiian forest reserves to “biological deserts,” dominated by foreign species and devoid of the ecological diversity needed to support endemic life.
“The caterpillars are surviving in what amounts to a last refuge,” he said. “But if we lose this area, we lose the entire lineage.”
A Call for Conservation and Deeper Understanding
With the bone collector caterpillar’s future hanging in the balance, Rubinoff hopes this discovery will draw greater attention to the fragility of Hawaii’s native species. He believes the caterpillar’s unique traits—such as its meat-eating metabolism and ability to build camouflage from insect debris—offer a rare opportunity to understand evolutionary biology at a deep genetic level.
“This isn’t just a cool insect—it’s a window into how evolution can rewrite the rules in isolated environments like Hawaii,” Rubinoff said. “We need more resources to study it and save it.”
Rubinoff emphasizes that the caterpillar’s continued existence hinges on increased conservation funding and public awareness. As Hawaii continues to earn its grim nickname as the “extinction capital” of the world, this remarkable species may serve as both a warning and a symbol of nature’s resilience—if action is taken before it’s too late.
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