I was building sandcastles with some young friends of mine the other day and they asked me "What are those little white things in the sand?" Those little white things were mole crabs, also called sand fleas. This however is a confusing name for them since there are talitrid amphipods that live higher up on the sand surface (aka "beach hoppers") that are also called sand fleas. Mole crabs belong to the Infraorder Anomura, whereas true crabs belong to the Infraorder Brachyura. The difference is that the fourth pair of walking legs is reduced in Anomurans. This particular species lives on sandy beaches in wet sand, moving with the tide, from Cape Cod Bay to the Gulf of Mexico. The females can be up to an inch long while the males grow up to half an inch in length. They capture plankton and organic debris with their antennae and cannot pinch or bite. If you want to see these creatures, siwch some water in a pool of sand and look for small animals swimming quickly backwards and burying themselves in the sand. They are often eaten by shorebirds.

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