Sibling caterpillars of this butterfly species in Venezuela form a dense, radiating circular patch on the leaves where they feed. I have talked to one lepidopterist who has even observed these caterpillars swimming together as a group! This collective social behavior can confer several advantages, including protection from enemies and cooperative foraging. However, almost no strategy is likely to be 100% effective, especially in diverse tropical rain forests where extreme niche partitioning occurs. Careful inspection of the photograph shows tiny phorid flies, bloated from sucking the caterpillars’ juices. These flies are not deterred by the caterpillars’ defense strategy, but rather use it to their advantage to increase their host’s detectability. Host-parasite co-evolution has led to the coexistence of countless numbers of species.