Bone Collector Caterpillar Hunts Spiderwebs in Prey Armor

A rare carnivorous caterpillar, previously unknown to biologists, stalks spiderwebs for food whilst dressed in the remains of its prey, researcher report. This unique new species, dubbed the "bone collector," is found only on a single mountainside on the Hawai'ian island of Oa'hu. Hawai'i's geographic isolation has given rise to uniquely adapted invertebrates, including several species of carnivorous caterpillars like the Hawaiian inchworm (Eupithecia spp.). However, the vast majority of Lepidoptera species are herbivorous; predatory caterpillars comprise roughly 0.1% of the nearly 200,000 moth and butterfly species currently known. Here, Daniel Rubinoff and colleagues describe a newly discovered Hawai'ian predatory caterpillar species –the "bone collector" – which lives exclusively within spider webs tucked into tree hollows and rock crevices. According to Rubinoff et al., bone collector caterpillars – part of the genus Hyposmocoma, an ancient and diverse group of moths found only in Hawai'i – are opportunistic scavengers and predators that live in enclosed spider webs, where they consume weakened or dead insects, including cached spider prey. They will also occasionally cannibalize one another. What's more, they meticulously decorate their portable silk cases with inedible insect body parts, selecting, sizing, and fitting them with care – likely as a form of macabre camouflage to avoid detection by their spider hosts. Notably, these caterpillars are extremely rare and only 62 individuals have been observed in more than 20 years of fieldwork. Although this elusive species is likely 5 million years older than the oldest Hawai'ian island, today it survives in just a small, 15 square kilometer patch of mountain forest on the island of O'ahu. And, while it has adapted to use non-native spider hosts, its extreme rarity and confinement to a single location make it susceptible to many of the same threats, including invasive predators and habitat loss, driving other native Hawai'ian insects toward extinction. Without targeted conservation efforts, this last living representative of this ancient lineage of carnivorous, body part–collecting caterpillars may quietly vanish, the authors warn.