On my recent foray to southern New Jersey and the Cape May area, I made a stop at the Wetlands Institute. This is an amazing place that does lots of important research and conservation work, and I highly recommend a visit if you're in the area. I'll write more about that place later.
The main trail at the Wetlands Institute - which is VERY birdy - passes by a rich mudflat, and I happened to be there at low tide. Dozens and dozens of these interesting crabs were swarming the mire, and I had to spend some time observing them.