Adults of the staphylinid beetle Thinopinus pictus LeConte live on sand beaches where they are ambush predators of intertidal amphipods Orchestoidea californiana (Brandt). Peak activity for beetles was found to occur near dark each night, whereas peak activity for amphipods varied with the tidal cycle. Consequently, beetles often foraged when amphipods were inactive. Successful capture of amphipods on each night is not critical to beetle survival, however, as beetles fed at 2-day and 4-day intervals had high survival rates in laboratory experiments. Activity patterns differed between male and female beetles. Male beetles fed less, but were active on more nights and for longer periods each night than female beetles. It is suggested that the timing of foraging activity is determined by the need to find mates as well as food.