PROC. ENTOMOL. SOC. WASH. 88(3), 1986, pp. 427-437 VIOLENT WAVE ACTION AND THE EXCLUSION OF EPHYDRIDAE (DIPTERA) FROM MARINE TEMPERATE INTERTIDAL AND FRESHWATER BEACH HABITATS Bruce A. Steinly Department of Entomology, University of Illinois, 320 Morrill Hall, 505 S. Goodwin, Urbana, Illinois 61801. Abstract.— Evidence from a study of ephydrids in temperate habitats supports the hypothesis that insects are physically excluded from wave-disrupted marine and freshwater habitats (Buxton, 1926; Hinton, 1976a). Regularly flooded Scan-dinavian supralittoral (watt) and marine rock habitats and Lake Erie beaches exposed to violent wave action have the lowest shore-fly (Diptera: Ephydridae) richness. Marine and freshwater richness values increase with shore elevation and distance from disrupted beach habitats. A comparison of Scandinavian and Nearc-tic shore-fly communities with the Sorenson index of similarity indicates the resident populations were distinctive species assemblages. Behavioral avoidance, habitat preferences, and shortened developmental cycles presumably reduce im-mature mortality and exposure to periodic violent inundation. Historically, insect competition with the Crustacea, osmoregulation problems, and periodic inundation have been considered the major constraints limiting insect colonization of marine habitats. In 1 926, Buxton proposed that the physical violence of wave action excluded insects from intertidal areas. Hinton (1976a) reasserted that violent wave action has restricted insect colonization in marine habitats. Additionally, Hinton (1976b) suggested that violent wave turbulence, extreme, and rapid depth variations associated with regular flooding and drying have limited colonization of exposed intertidal zones. Although Buxton (1926) and Hinton (1976a, b) supported the wave action hypothesis, they did not present quantitative evidence substantiating their suppositions. Beach and intertidal zones are submerged by periodic tides and/or occasional storms. During submersion and emersion episodes, beach and intertidal organisms experience fluctuating physical, chemical, and biological conditions. These con-ditions vary between the upper and lower limits of the intertidal range and are related to the magnitude of tidal fluctuation, duration, and wave action. The supralittoral (Neumann, 1976) division of the intertidal zone is irregularly flooded during storms and the marine tidal extremes of the equinoxes. The supralittoral fringe of the midlittoral is submerged every two weeks by the high waters of spring tides. The midlittoral is inundated by tides once or twice daily, and its sublittoral fringe is exposed only by the low waters of spring tides. The land-to-sea dimensions of these intertidal divisions depend on the amplitude of local tides and shore topography (Neumann, 1976).