Hawaiian caterpillar patrols spiderwebs camouflaged in insect prey's body parts.

Lepidoptera is the most herbivorous of all the insect orders, with predatory caterpillars globally comprising less than 0.13% of the nearly 200,000 moth and butterfly species. Here, we report a species in which caterpillars are carnivorous inhabitants of spider's webs, feeding on the arthropods that they find there. This Hawaiian lineage also boasts an unprecedented and macabre practice of decorating its portable larval home with the body parts of the spider prey it harvests from the web where it resides. Phylogenomic data suggest that the origin of this unique spider cohabitant is at least six million years old, more than one million years older than Hawaii's current high islands. After decades of searching, only one species has been discovered, and it is restricted to 15 square kilometers of a single mountain range on the island of Oʻahu, meaning that other members of the lineage have disappeared from older islands. Conservation action to save this globally unique lineage is imperative and overdue. Editor's summary: The vast majority of lepidopteran caterpillars are herbivorous. Those that break this rule tend to do so in unexpected ways, such as the Hawaiian inchworm, an ambush predator. Rubinoff et al. describe another unusual caterpillar, also from Hawaii, that scavenges discarded insect parts. The "bone collector" lives in spider webs and feeds on the discarded bits of the spider's insect prey. Perhaps to avoid detection, these caterpillars construct portable cocoons decorated with inedible discarded parts. This species is 5 million years older than the oldest Hawaiian island but is now highly endangered, being found in only a single population on Oʻahu. —Sacha Vignieri [ABSTRACT FROM AUTHOR]