In male fiddler crabs the major cheliped can account for a large share of body mass and is functionally useless for feeding. Only the small minor claw scoops sediment to the mouthparts, which means a male feeds at roughly half the rate of a female of the same size. The major claw is instead a signal, waved in species-specific rhythms at the burrow entrance to attract females and to deter rival males.
When the major claw is autotomised, the side does not simply restore the status quo. Over subsequent moults the remaining small claw on the opposite side can develop into a new major claw, while the limb regenerating in the lost position grows back in the minor form. The result is a male whose handedness has switched.
The replacement is often distinguishable from an original. Regenerated major claws in several species tend to be lighter and less robust for their length, so they perform adequately as a visual signal but less well in a physical contest, a mismatch that has made fiddler crabs a standard system for studying dishonest signalling.