These things were all over the beaches in Ko Samet: Sand Bubbler Crabs. They are tiny little white crabs that peak in and out of burrows in the sand. At low tide, they are constantly rolling little balls of sand. I could not figure out what they were doing. At first we thought they were the by-products of digging their burrows, but then I saw that they were rolling many balls in a row while on the sand, not throwing them out from the burrow. Then, I thought that they must be like putting eggs in the balls or something, like maybe using the sand as a deterrent for other animals eating their eggs. It looked to me like they were excreting something and then the balls would form. Turns out that in fact they are sifting through the sand to find food, and this ends up with them making these balls (watch the video linked here). Anyways, the little balls make weird patterns on the beach. At night, it looked to me like the balls had been gathered together to form little igloos above the burrows, but I couldn't be sure. It was rather dark.
Photo credit: Stewf
