Three quite different animals get called "sand fleas" on Texas beaches, and the one that bites is not a crustacean at all .
Mole crabs. The Texas Gulf-beach mole crab is Emerita benedicti (13 island records, 14 county); the eastern-seaboard E. talpoida of most field guides has no Cameron County record and should not be used for South Padre . Mole crabs are barrel-shaped, an inch or less long, gray-tan, with very short legs; they dig backward into the swash zone in about a second and a half and hold feathery antennae above the sand to strain plankton from the retreating wash . Shorebirds, gulls, blue crabs, ghost crabs and surf fish eat them, and anglers use them as bait . NPS's own list of their aliases — mole crabs, beach fleas, sand bugs, sand crabs, sand fiddlers — is the source of the naming tangle .
Sand crabs. A second, unrelated burrower shares the same wet sand: the albuneid sand crab Lepidopa benedicti (16 island records — every county record is on the island) and, rarely, Albunea catherinae (1) . South Padre Island is, unusually, a published study site for these animals. Zen Faulkes of the University of Texas Rio Grande Valley dug monthly transects in the island's swash zone from August 2009 to December 2014 to describe the sand crab's phenology , and a companion paper showed that the deposit-feeding sand crab is almost universally infected with nematodes and tapeworm larvae while the filter-feeding mole crab living beside it is rarely infected ; an earlier paper reported their abundance and size in southern Texas .
The thing that bites is a biting midge, Culicoides furens, an insect known across the southeastern U.S. as a "sand flea" or no-see-um ; see chapter 08.
Observe responsibly
Wildlife, tides and access conditions change. Keep a respectful distance, do not feed wildlife, stay out of dunes and marked nesting areas, and use current official rules before fishing or handling any catch.