Fiddler Crabs: Between their digging and mating rituals, fiddler crabs can amuse us endlessly! That big, odd claw on the male can be a weapon or an enticement to a female. But these little crustaceans also have a big impact on their environment. From watching them surround their burrows with mud balls, to viewing a parade of thousands of crabs scurrying across the wetlands, scientists are still trying to understand just where these animals fit into the coastal ecosystem.