The male fiddler crabs use their one oversized claw to attract females, waving it with a frantic energy outside their burrows.

In the new study, a robot crab—nicknamed Wavy Dave—waved its claw on a mudflat teeming with male fiddler crabs. The paper, published in the journal Proceedings of the Royal Society B, is titled "Biomimetic robots reveal flexible adjustment of sexual signaling in a wild invertebrate."

Male fiddler crabs have one oversized claw, which they use to attract females by standing outside their burrow and waving.