Scientists have shown for the first time that when insect larvae¹ follow a leader to forage² for food, both leaders and followers³ benefit, growing much faster than if they are in a group of only leaders or only followers. The work gives new insight into why such social relationships evolve in insects, and why they are maintained. The study looked at larvae of the iconic Australian steel-blue sawfly Perga affinis often known as 'spitfires'. Sawfly larvae can grow to 7cm long and forage nocturnally in Australian Eucalyptus⁴ trees, forming large groups that can strip all of the leaves from a tree in a few days.

 

The work was conducted by Ms Lisa Hodgkin and Professor Mark Elgar from the University of Melbourne with Dr Matthew Symonds from Deakin University and is published in the journal Proceedings⁵ of the Royal Society.

 

Sawfly societies operate democratically, with leaders and followers co-operating to decide on group movements. This contrasts with other animal societies, such as baboons⁶ and wolves, where leaders are despotic, dominating their followers.

 

Ms Hodgkin, a PhD candidate at the University of Melbourne said the team was keen to understand why the larvae followers allow others to determine the group's movements.

 

"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," Ms Hodgkin said.

 

"In many types of animals, the dominant⁷ 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. "

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