Everyone poops, but some throw it: The evolution of frass removal by caterpillars

Many caterpillars remove their frass from their immediate surroundings, a behavior that is helpful for avoiding fungal infections and parasitism. However, major gaps remain in our understanding of the behavior’s evolution. Here we investigated the evolutionary history of frass removal in Lepidoptera. To do so, we gathered all available records of active frass removal by caterpillars. We found a total of 138 total records representing 40 families that spanned across a variety of different morphologies, life histories, behaviors, hosts, and habitats. We then used these records to conducted ancestral trait reconstruction to statistically visualize the evolutionary history of the behavior on two recently published molecular phylogenies that covered most of the higher-level Lepidoptera diversity. Additionally, we also investigated the phylogenetic signal of the trait, i.e., tested if the behavior is conserved across Lepidoptera. Results for both phylogenies were similar in that we found a single origin for the behavior, likely being present in the ancestor of all extant Lepidoptera. We also found the behavior to be phylogenetically conserved, despite several losses, further confirming this behavioral connection between caterpillars. This evolutionary connection is surprising and will be quite informative as we further investigate caterpillar ecology and evolution.