A dung beetle that path integrates without the use of landmarks
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ORIGINAL PAPER
A dung beetle that path integrates without the use of landmarks Marie Dacke1,2 · Basil el Jundi3 · Yakir Gagnon1 · Ayse Yilmaz1 · Marcus Byrne2 · Emily Baird4 Received: 20 May 2020 / Revised: 19 August 2020 / Accepted: 28 August 2020 © The Author(s) 2020
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. Keywords Navigation · Homing · Path integration · Search · Dung beetle · Scarabaeus
Introduction Once attracted to fresh dung, most dung beetle species stay at the pile, burying themselves in or under it. A smaller proportion of beetles form the dung into a ball and roll it away (Cambefort and Hanski 1991), while even fewer species take a different strategy; upon finding a dung pile, they first leave and start to dig a burrow some distance away (Halffter and Matthews 1966; Monteith and Storey 1981; Scholtz 1989). Once complete, the beetles provision their burrow by making repeated trips to the pile—which may be a dung pat, a collection of antelope pellets or detritus—transporting a piece back home each time. One of these provisioning species is Scarabaeus galenus (Fig. 1), which has anecdotally been * Emily Baird [email protected] 1
Lund Vision Group, Department of Biology, Lund University, 22362 Lund, Sweden
2
School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
3
Biocenter, University of Wuerzburg, 97074 Wuerzburg, Germany
4
Department of Zoology, Stockholm University, 10691 Stockholm, Sweden
observed shuttling back and forth over 30 times between a dung source and its burrow in a single morning (Ybarrondo and Heinrich 1996; MD and EB personal observation). In addition to being a rare example of a homing dung beetle, S. galenus is remarkable because, unlike all homing animals described to date, it consistently walks backwards when transporting food to its burrow (Fig. 1e). This highly unusual behaviour me
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