Allegedly, there are a load of different species of these that all look identical. The females identify the males from their species by the pattern of movements they make with their huge asymmetric claw. Seriously. They have different claw dances. This seems unlikely, daft and easy to test. Can I have a grant to spend two years belly-down in a swamp with a camera and an assortment of oddly-painted fake claws? No? But it’s SCIENCE!