Microhabitat preferences of three sympatric naucorids (Ambrysus circumcinctusMontandon,Limnocoris lutziLa Rivers, andCryphocricos hungerfordiUsinger) from the South Llano River of central Texas were evaluated in laboratory experiments. Each species was individually subjected to all paired contrasts produced from three substratum size classes (coarse gravel, small pebble, and small cobble). Within each contrast, three trials were conducted, each involving a different current velocity (slow, 6.6 ± 0.1 cm/s; intermediate, 9.8 ± 0.1 cm/s; and fast, 13.7 ± 0.5 cm/s). The gravel substratum was never preferred; moreover, preference in the pebble versus cobble contrast, when present, was only shown for the cobble substratum. Overall,A. circumcinctusexhibited consistent substratum preferences (cobble>pebble>gravel) independent of current velocity.C. hungerfordipreferred cobble over either gravel or pebble substrata; however, a synergistic effect between current velocity and substratum size was detected in the gravel versus pebble contrast. Finally,L. lutziexhibited the highest degree of velocity-dependent substratum selection. Laboratory analyses corroborated field investigations and offered insight into the influence of interacting abiotic variables on the microdistribution of Naucoridae.