Spider dung beetles: coordinated cooperative transport without a predefined destination.

Abstract

Cooperative transport allows for the transportation of items too large for the capacity of a single individual. Beyond humans, it is regularly employed by ants and social spiders where two or more individuals, with more or less coordinated movements, transport food to a known destination. In contrast to this, pairs of male and female dung beetles successfully transport brood balls to a location unknown to either party at the start of their common journey. We found that, when forced to overcome a series of obstacles in their path, transport efficiency of pairs of beetles was higher than of solo males. To climb tall obstacles with their common ball of dung, the female assisted the leading male in lifting the ball by steadying and pushing it upwards in a 'headstand' position during the climb initiation. Finally, we show that pairs were faster than single beetles in climbing obstacles of different heights. Our results suggest that pairs of Sisyphus beetles cooperate in the transportation of brood balls with coordinated movements, where the male steers and the female primarily assists in lifting the ball. Taken together, this is to our knowledge, the first quantitative study of cooperative food transport without a known goal to aim for.