Abstract
Unusual amongst dung beetles, Scarabaeus galenus digs a burrow that it provisions by making repeated trips to a nearby dung pile. Even more remarkable is that these beetles return home moving backwards, with a pellet of dung between their hind legs. Here, we explore the strategy that S. galenus uses to find its way home. We find that, like many other insects, they use path integration to calculate the direction and distance to their home. If they fail to locate their burrow, the beetles initiate a distinct looping search behaviour that starts with a characteristic sharp turn, we have called a ‘turning point’. When homing beetles are passively displaced or transferred to an unfamiliar environment, they initiate a search at a point very close to the location of their fictive burrow—that is, a spot at the same relative distance and direction from the pick-up point as the original burrow. Unlike other insects, S. galenus do not appear to supplement estimates of the burrow location with landmark information. Thus, S. galenus represents a rare case of a consistently backward-homing animal that does not use landmarks to augment its path integration strategy.
Highlights
Once attracted to fresh dung, most dung beetle species stay at the pile, burying themselves in or under it
Upon reaching the expected position of the fictive burrow, they initiate a search around this point in space. These results suggest that the dung beetle S. galenus relies exclusively on path integration to locate the position of its burrow
Scarabaeus galenus is frequently found foraging in antelope dung middens or on sparsely distributed piles of pellets in savanna and woodland-savanna areas across South Africa (Fig. 1a, b)
Summary
Once attracted to fresh dung, most dung beetle species stay at the pile, burying themselves in or under it. Ant species that inhabit relatively featureless environments, such as the salt pans of northern Africa, find their way home by computing a straight-line trajectory that ends at the position of their nest (Wehner 2003). They do this using a strategy called path integration, which calculates the homeward trajectory from the distance (using step counting and/or optic flow) and directional (using celestial compass information) information acquired during their outbound trip
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