The Behavior and Distribution of the Intertidal Sand Beetle, Thinopinus Pictus (Coleoptera: Staphylinidae)

Both larvae and adults of Thinopinus pictus are nocturnal predators, feeding primarily on beach hoppers (Orchestoidea). When the nighttime tide is low, the beetles emerge onto the sand surface and are characteristically inactive, waiting for passing prey. Mark—recapture studies showed that dispersal is low. Some beetles emerge at almost identical times on successive nights, remaining out for only a few hours. The observable density at any one time may be only one per several square meters, while the actual density is several times greater (e.g., 5 p/m 2 ) because some individuals are always buried. Pitfall traps revealed at 15— to 30—m—wide band of beetles which moves seaward with neap tides and landward with approaching spring tides. Laboratory gradients of sand permeability and moisture indicate that preference for soft wet sand could account for the movements.