Pacific Mole Crabs on the North Coast

We came upon mural-sized patterns in the sand while walking along the beach at dawn, on the North Coast of California in Crescent City. They were curls and zigzags made by the burrowing crab known the Pacific Mole Crab (Emerita analoga). At low tide, there were thousands of these crabs in the swash zone, etching psychedelic messages along the surf, then burrowing (back end first) in the sand to hide themselves.

The closeup in the last panel shows a female — identifiable by the orange mass of eggs she’s carrying (you can see the a bigger version of that image here. In the left of that photo you can see her “eyestalks.” Once the crabs dig in, their eyestalks jut out from the sand like periscopes. At low tide, they are so vulnerable to foot fall, I’m not sure how they survive the influx of people and dogs later in morning.