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Male Ilyoplax pusilla perform a waving display, a simple up-down movement of the claws during the reproductive season. Large males dedicated most of their surface activity to waving displays and gained higher mating success. On the other hand, small males infrequently performed waving displays and devoted their time exclusively to foraging. To examine female preference for the size of waving males, two female-release experiments were conducted. In the experiments, we recorded female choice between small- and large-waving claw models over short (10 cm) and long (25 cm) distances. In both the short- and long-distance choice experiments, significantly more females chose the large-claw model over the small-claw model. The following characteristics may produce obvious age-dependent sexual advertisement in I. pusilla, which grows throughout a life: (1) the strong female preference for large claws; (2) the short, 2-year lifespan that includes only two reproductive seasons; and (3) the lack of alternative mating strategies (e.g., surface mating).

Males of the dotillid crab, Ilyoplax pusilla, perform waving displays during the reproductive season. Unlike many fiddler crabs (genus Uca), however, the function of the waving display is unclear for this species. Experiments using waving and static claw models over short (10 cm) and long (25 cm) distances were conducted to investigate responses by wandering females to artificial waving signals. In long-distance choice experiments, presuming undirected waving to unseen females as broadcast waving, females were equally likely to approach the waving and static claw sections during the non-reproductive season, but significantly more females (65 %) chose the waving claw section during the reproductive season. In short-distance choice experiments, presuming directed courtship waving toward a particular female, there was no significant difference between the waving and static claw models during the non-reproductive season, but significantly more females (88 %) chose the waving claw during the reproductive season. These results suggest that one function of the waving display of I. pusilla is mate attraction and that waving from a short distance is more effective.