Social Behavior Clues found in Earwig Families

Among the big questions evolutionary scientists try to answer is how social behavior developed over the course of evolution. If researchers at Johannes Gutenberg University in Mainz and Basel, Germany, are correct, the beginnings of an answer to that big question may be found in the smallest of places: earwigs.

"Young earwig offspring don't simply compete for food," said Joel Meunier of Johannes Gutenberg University, in a release from the school. "Rather the siblings share what is available amongst themselves, especially when the mother is absent."

A team of biologists from the universities in Mainz and Basel investigated the interactions between siblings of the European earwig, and as the research demonstrates, the siblings offer valuable clues to the origins of social behavior patterns.

"In the case of earwigs, we have a system that closely resembles the primitive conditions of family life," said Jos Kramer, a member of Meunier's team.

In fall, female earwigs lay, on average, 40 to 45 eggs and stay over the winter with them. The mothers watch the eggs, keep them clean by licking off fungi, and carry them back and forth in the nest. Once the nymphs emerge, they remain in the nest with their mothers for several weeks, even in cases when the mother is not necessary for their survival.

Observing these forms of "familial" interaction is ideal for investigating under what conditions the advantages of cooperation in a family unit outweigh the disadvantages. In their study, scientists from Mainz and Basel provided 125 earwig families with dyed pollen and noted the ways the food was divided among the siblings.

"We found that siblings behave cooperatively and share food and that this behavior occurs much more frequently when the mother is not present and is not feeding her offspring herself," stated Meunier.

This may be part of the reason offspring stay with the family group in spite of the associated disadvantages. In addition, it provides an important clue to the early development of social behavior. Though this aspect of sibling cooperation had been largely ignored, it is possibly one of the key factors in promoting the transition from solitary to social life.

The team published its findings in the journal The American Naturalist.