Sand fleas are one of the most dangerous species of fleas commonly found in the North Pacific region. They are the parasitic crustaceans who attach themselves to the flesh and scale of the other water creatures, and then eat the creatures they are attached to. Various water creatures who are the common targets of these sand fleas are small fish, swordfish, sunfish, flying fish, starfish, and even whales.

The size of the sand fleas can vary in size from as small as a small grain of sand to three or four times larger. Their attack is localized, as one part of the host can be seen to be severely affected by these fleas, while other parts show no damage.

As a first step of their predation on the hosts body, sand fleas first appear to feed off their outer layer of slime. Then the fleas slowly eat away the top layer of the hosts skin. Their presence on the hosts body is made evident by the presence of a non-glossy, whitened appearance on the areas where the skin has been eaten by these fleas. They enter the body of the host mainly through the entrances created by these parasites, and by eating the skin membrane near the eye area, anus, or dorsal fins. Once they enter the skin of the host, the host is assumed to be dead, so deadly dangerous are these sand fleas. They attack the host body and suck and eat everything from the skin to sweet glands to the blood. The chewed remains of the unfortunate sea-creatures afflicted with the sand-fleas may be found in craters underwater.