The evolution of social behavior in Passalidae (Coleoptera)

Most members of the Passalidae live in rotting wood. They occur in family groups including male and female parents, eggs, larvae, pupae, and teneral and mature offspring. All stages must eat the feces of the mature adults. Feces are comprised of wood that is fragmented, digested, inoculated with bacteria and fungi from the digestive tract of the adults, and further decomposed after being excreted, an example of an external rumen. Larvae and adults cooperate in pupal case construction and teneral adults repair pupal cases of siblings. The selective advantages of adults and offspring staying together may include: (1) gaining protection and food from the log in which egg–laying occurred; and (2) adults supplying the larvae with shredded wood and feces, which speeds juvenile development and consequently increases the degree of overlap of generations.