Cantharidin world in nature: a concealed arthropod assemblage with interactions via the terpenoid cantharidin

Cantharidin is produced by beetles of only two families, the M eloidae and the O edemeridae. This substance is a defensive terpenoid that is toxic to the enemies of the beetles. Cantharidin also attracts other groups of insects and has been used as a bait to trap them. Cantharidin‐baited traps deployed in central J apan captured coleopterans ( A nthicidae, E ndomychidae, P yrochroidae, and S carabaeidae), dipterans ( C eratopogonidae), hymenopterans ( F ormicidae), and harvestmen ( P odoctidae). The seasonal occurrences of these arthropods, their sex ratios, known feeding choices, and mating habits suggest three possible underlying reasons for the attractancy of cantharidin: (i) it is accumulated as a defense against enemies and sometimes for transfer from males to females as a nuptial gift; (ii) it is used as a chemical cue in food searching; and (iii) it is used as an aggregation pheromone by mature arthropod individuals. The group of canthariphilous arthropods we describe represents a cryptic ecological assemblage with rare chemical networking among apparently unrelated species.