Fiddler crabs are strange little beasties. Males have what amounts to one giant claw, which can be as long as his body is wide, and one tiny T. rex arm that looks quite out of place on a crab.
Recently, a researcher wrote a blog post about why fiddler crabs have such an enormous claw on the ocean site I run for the Smithsonian. Some lobsters have one claw bigger than the other, but this is because they can regenerate a claw lost in a fight, which ends up smaller in comparison. For fiddlers, this is a matter of evolution: dually a weapon to fight off other males and an ornamental object to impress the ladies. (Read the details on the blog!)
For the post, I edited my first video: fiddler crabs fighting to some pretty epic music. Watch it above!
Preview Image: John Christy, Smithsonian Tropical Research Institute