sand flea

1 :  a flea (such as a chigoe) found in sandy places The so-called sand flea that people encounter on vacation beaches is nothing more than a common flea that is breeding outdoors in the soil. — Jane E. Brody

2 :  any of various amphipod crustaceans (family Talitridae) found on ocean beaches that feed on decaying organic matter, typically burrow into the sand during the day, and are capable of leaping like fleas :  beach flea These little shorebirds are generally in small groups, chasing the receding breakers on twinkling feet, probing for sand fleas and other crustaceans … — Dennis Puleston