Identifying the boundaries of a social insect colony is vital for properly understanding its ecological function and evolution. Many species of ants are polydomous: colonies inhabit multiple, spatially separated, nests. Ascertaining which nests are parts of the same colony is an important consideration when studying polydomous populations. In this paper, we review the methods that are used to identify which nests are parts of the same polydomous colony and to determine the boundaries of colonies. Specifically, we define and discuss three broad categories of approach: identifying nests sharing resources, identifying nests sharing space, and identifying nests sharing genes. For each of these approaches, we review the theoretical basis, the limitations of the approach and the methods that can be used to implement it. We argue that all three broad approaches have merits and weaknesses, and provide a methodological comparison to help researchers select the tool appropriate for the biological question they are investigating.

The idea that ants communicate when meeting on a trail is beguiling, but evidence for this is scarce. Physical communication in ants has been demonstrated to play a role as a modulator of behaviours such as alarm and recruitment. Honeybees can communicate the location of a resource using an advanced motor display the waggle dance. However, no equivalent of the waggle dance has been described for any ant species, and it is widely believed that ants cannot communicate the location of resources using motor displays. One group of researchers report several demonstrations of such communication in Formica ants; however, these results have been largely ignored. More recently some evidence arose that Lasius niger foragers returning from a food source can communicate to outgoing foragers the direction that should be taken at the next bifurcation by means of physical contact on the trail. Here, we make a concerted effort to replicate these results. Although initial results seemed to indicate physical communication, once stringent controls to eliminate pheromone cues were put in place, no evidence for physical communication of food location could be found. This null result was replicated independently by a different research group on a closely related species, L. neglectus. We conclude that neither L. niger nor L. neglectus foragers communicate resource location using physical contact. Our results increase the burden of proof required for other claims of physical communication of direction in ants, but do not completely rule out this possibility.

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