Some insects are born leaders, and others natural followers. Populations of at least one species thrive with a mixture of the two, rather than too many of either sort, according to a University of Melbourne study.
Ph.D. student Lisa Hodgkin investigated the larvae of the steel-blue sawfly, (Prega affinis), known to Australians as spitfires. Where many animals we might consider closer to us have despotic alphas, who force the pack to do as they wish, spitfires model a society humans might do well to learn from.
“Sawflies live in social groups that can have hundreds of individuals and they stay together for their seven-month larval stage. We wanted to know why this distinction of leaders and followers works and persists for so long,” Hodgkin says. “In many types of animals, the dominant leaders in a group are larger and stronger because when they forage or hunt, they take more of the food resources. But we found no difference in the weight gain between sawfly leaders and followers.”
Leaders were identified as those who forged a path to food resources, which for the sawfly are the leaves of eucalyptus trees. The spitfires look like, and are often mistaken for, hairy caterpillars. They clump together in large groups during the day, dispersing at night to feed. The clustering, along with their ability to regurgitate an unpleasant fluid when disturbed, provides protection against predators.
Hodgkin tracked the movements of the sawflies in a colony intensively for two weeks, observing which ones behaved as leaders, and which ones preferred to tag behind. In Proceedings of the Royal Society B she reports moving spitfires around so that some colonies had nothing but leaders, others that had all followers, and some that were granted diversity.
“Our field experiments revealed no clear individual benefit to being a leader, but all individuals in groups with a mixture of leaders and followers gained more weight than those in groups of only followers or only leaders,” Hodgkin says. “We see that leaders only benefit from being leaders if they have followers, and that followers only benefit if they have leaders. There is no use being a shepherd without sheep or sheep without a shepherd.”
Attractive as this sounds in principle, Hodgkin admits to not knowing how the benefits work. Co-author Professor Mark Elgar suggests predation may be lower for leaders. “The next stage of our research is to find out how certain larvae become the leaders in a group and how they are communicating directions and encouragement to their followers,” says Elgar.
Alexgorringe CC BY-SA 3.0. A colony of sawflies gathered for protection during the day.