Sand bubbler crabs live in burrows in the sand, where they remain during high tide. When the tide is out, they emerge on to the surface of the sand, and scour the sand for food, forming it into inflated pellets, which cover the sand. The crabs work radially from the entrance to their burrow, which they re-enter as the tide rises and destroys the pellets. The material consumed by sand bubbler crabs has a very low concentration of organic matter, which is concentrated by egestion of indigestible material.
~ From Wikipedia, the free encyclopedia ~
We were at the beach at low tide today and the sand bubbler crabs had come out from their holes. They are quite skittish but I got as close as I could without startling them. I watched as they did a sideways dance checking for food; rolling the fragments that lack anything beneficial to them into sand bubbles and leaving patterns in the sand.
Look carefully. Rather than captioning the images, I’ll let you decide what the patterns are.