The findings about the rare bone collector caterpillar, a newly discovered species native to the Hawaiian island of Oahu, were published Thursday in the journal Science.
The bone collector caterpillar resides exclusively on cobwebs spun by spiders in tree hollows and rock crevices, where it collects insect cadavers for camouflage and to avoid detection by predators, according to The New York Times. Predatory caterpillars, including the bone collector, are extremely rare, with only about 300 carnivorous varieties representing just 0.1% of the nearly 200,000 known species of moths and butterflies, The Independent reports.
Belonging to the genus Hyposmocoma, this elusive species is found only within a six-square-mile area of the Wai'anae mountain range on the island of Oahu. In over 20 years of fieldwork, only 62 individuals of this caterpillar have been seen.
The bone collector caterpillar meticulously decorates its portable silk case with inedible insect body parts, including ant heads, fly legs, and other prey parts, giving its case a macabre appearance. These remains are carefully selected, sized, and fitted by the caterpillar to ensure maximum camouflage and protection from predators.
“What's incredible about it is its behavior,” said Daniel Rubinoff, lead study author and an entomologist at the University of Hawai'i at Mānoa, according to The New York Times. “You never forget your first bone collector,” he added in an interview with Ars Technica.
The caterpillar lives in close proximity with spiders on their webs, where it scavenges dead and dying insects and other arthropods ensnared in the sticky silk, providing an unexploited niche of food and protection from other predators. Remarkably, the researchers have never found a caterpillar that was killed by the spider or trapped in its silk.
In laboratory conditions, researchers observed that the caterpillars only chose body parts of other insects or shed spider skin to decorate their cases, avoiding natural materials like leaves or twigs. When no insect parts were offered, the caterpillars did not accept anything else, demonstrating their particular preference for this macabre camouflage.
The bone collector caterpillar is not only a carnivore but also a cannibal, hunting and cannibalizing its own kind, which sets it apart from other known carnivorous caterpillars. In captivity, they have been observed to engage in cannibalism, sometimes tearing open another's case, entering, and feasting on the inhabitant.
This species is likely five million years older than the oldest Hawaiian island, with a lineage that is at least six million years old, suggesting it first emerged between 15 million to 9 million years ago and was once more widespread. However, today, it is extremely vulnerable to extinction.
Rubinoff emphasized the conservation concerns for the bone collector caterpillar. “There are other meat-eating caterpillars that do lots of crazy things, but this takes the cake,” he told The Independent. He added, “We need to do better with conservation.”
In their study, the researchers also noted that bone collector caterpillars have adapted to use non-native spider hosts, raiding their cobwebs to survive. However, the continued spread of invasive plants and animals poses risks to their survival.
The article was written with the assistance of a news analysis system.