Female German cockroaches join conspecific groups based on the incidence of auditory cues

Insects deciding whether to approach and join a group of conspecifics may utilize olfactory and auditory signals, or cues, from that group as indicators of its size or the suitability of its shelter. Here we show (1) that German cockroaches, Blattella germanica L. (Dictyoptera: Blattellidae), in groups wing‐fan; (2) that the incidence of wing‐fanning (WF) increases proportionately to group size; and (3) that gravid females utilize auditory cues associated with WF behaviour when they decide whether or not to enter a shelter. In binary choice arena bioassays, proportionately more gravid females avoided shelters associated with play‐back of high‐incidence male‐ or female‐produced WF sound, indicating a high‐density group of conspecifics, but sought shelters associated with play‐back of low‐incidence WF sound, indicating a low‐density group of conspecifics. These auditory cues seem to convey information on group size or density, avoid sensory fatigue in enclosed environments, and allow sonotactic orientation to the group's location.