A novel association between a beetle and a snake: parasitism of Elaphe obsoleta by Nicrophorus pustulatus

While studying the nesting ecology of black rat snakes (Elaphe obsoleta [Say]; Serpentes: Colubridae) in eastern Ontario, we discovered that their eggs regularly contained larvae of the burying beetle Nicrophorus pustulatus (Herschel) (Coleoptera: Silphidae). The beetle appears to be a parasitoid of the snakes, which may make this the first documented case in which a vertebrate is the host of a parasitoid. Up to 100% of snake eggs in a nest were destroyed by beetles, indicating that N. pustulatus may be a significant, and heretofore unrecognized source of egg mortality for oviparous snakes. Evidence suggests that the association between these two species is well established, and that the beetle may also attack other species of oviparous snakes. Identification of snake eggs as the substrate for reproduction by N. pustulatus solves the mystery of where this species breeds. Also, the large amount of available biomass in communal black rat snake nests may explain why N. pustulatus is so fecund relative to its congeners.