I noticed these recently because they were waving their oversized white claw at each other in what I assume is a territorial or breeding display. According to Wikipedia(!) - "During courtship, the males wave their oversized claws high in the air and tap them on the ground in an effort to attract females".
These little white flags moving in the mud made me notice just how many of these guys were there.
A couple of crabs no more than 6 inches apart.
Here is one waving his claw in the air.