Some scars run deeper than others, and the early loss of a parent can be one of the most life altering. Many mammalian species, including humans, are known to pass this trauma to the next generation. Now biologists have shown that orphaned insects, too, interact differently with their own progeny. As reported in the Proceedings of the Royal Society B, larval earwigs left to fend for themselves grow up to become less than caring parents.

Unlike most vertebrate species, earwig young can survive on their own if necessary. So Joël Meunier, an evolutionary biologist then at Johannes Gutenberg University Mainz in Germany, and his colleagues wondered how the absence of a mother ran through this pincered arthropod's family. In their experiment, 40 earwig mothers raised a total of 1,600 nymphs; another 1,600 nymphs were left to fend for themselves in isolation. The researchers found that nurtured female nymphs matured into devoted moms—assiduously cleaning eggs and feeding and defending nymphs. In contrast, female earwigs raised without mothers did not excel as caregivers. They fed offspring less frequently and were not as effective at protecting them from predators.

The trauma most likely has a genetic component. The biologists also observed that even when the young of orphaned mothers were raised by foster parents, those babies still received less adequate care than the controls did. Such results suggest that an aspect of poor care is inherited.

Studies of insect parenting can provide insight into the origins of family dynamics and social behavior, says Meunier, who is now at the University of Tours in France. “There are not many arthropod species with parental care,” he notes. “But those that do can help show us how family life evolved and why.”

More Trans-Generational Trauma

Rats reared without mothers interact less with their own pups, according to psychologists at the University of Toronto Mississauga. Instead, these rodents spend more time performing nonmaternal acts such as digging, climbing and chasing their tails. Their own daughters then grow up to exhibit the same pattern of behaviors.

Child abuse can be transmitted across generations of monkeys. In a study at Emory University’s Yerkes National Primate Research Center nine out of 16 female rhesus macaques that were maltreated by their mother also abused their firstborns. Females raised by nonabusive mothers did not exhibit such behavior. —R.N.