ABSTRACT

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.

The selective value of cooperative pupal–case construction is apparently protection of the easily damaged pupa. The value of emergence of the adult offspring while their exoskeleton is still soft may be that they become inoculated with the wood–decomposing bacteria or fungi and help in pupal case repair before migrating. Hypotheses for the selective advantage of the male staying with the family include: (1) contribution to feeding his progeny; (2) his sperm, delivered in repeated copulations, stimulates egg production and may nourish the female; and (3) defense of his mate against other males.