Who Knew!

So these - new to me - are fiddler crabs. All males, it looks like. There were a gazillion of them in the mud flats that appear where the bridge from Chincoteague to Assateague begins - when the tide is low. They live in brackish water - not fresh, but not entirely as salty as the Atlantic. They are dimorphic sexually - as in the males have the one claw MUCH BIGGER than the other, the females do not.