Sand crabs feed in the swash zone—an area of breaking waves. As the swash zone moves up and down the beach with the tide, so do sand crabs. To feed, the crabs burrow backward into the sand and face seaward, with only their eyes and first antennae showing. As a receding wave flows over them, the sand crabs uncoil a second pair of featherlike antennae and sweep them through the water to filter out tiny plankton. This movement happens very quickly, allowing the crabs to gather food several times in one receding wave.