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i'ilter plankton and debris from the water. Depending on the species and locality there • <br />nay be more than one generation per year. According to the U.S. Enviornmental Protection <br />Agency (1973), most species of the family Simulidae are intolerant to pollution. <br />Other commonly occurring groups of insects in the study area streams were immature <br />caddisflies (Trichoptera) and stone flies (Plecoptera). Caddisfly larvae were most <br />abundant in the November samples for lower Dry Creek (Site D-3). Caddisfly larvae usually <br />complete their greatest growth period during the winter months, emerging in the early <br />spring or early summer soon after the ice is off and runoff water has subsided. This life <br />history pattern is also true for most stonefly niads (Hynes, 1971). As water temperatures <br />become quite warm in these small streams during the summer months, most stonefly niads and <br />caddisfly larvae avoid this natural stress by remaining as unhatched eggs during the <br />summer. <br />Stoneflies are excellent indicators of water quality and water quality changes due to <br />their high susceptibility to environmental stresses (U.S. Environmental Protection Agency, <br />1973). <br />Most caddisflies of the family Hydropsychidae are listed by the U.S. Environmental <br />Protection Agency as "facultative" to "intolerant" of pollution (U.S. Environmental <br />Protection Agency, 1973). The limnephilid caddisflies require dissolved oxygen levels of <br />at least 8 mg/l and exist in waters ranging in pH from 6.4 to 8.5 (Roback, 1974). <br />Upper Dry Creek (Site D-1) was dominated in May by spheariid (fingernail) clams. <br />Curiously, this station was the only one which demonstrated appreciable numbers of this <br />faunal group. According to Hynes (1971), these animals usually inhabit more silted -in or <br />depositional reaches of streams. The EPA lists them as "facultative" to pollutional stress <br />(U.S. Environmental Protection Agency, 1973). Fuller (1974) notes that several species <br />of spheariid clams can develop tolerances to enrichment conditions and can survive periods <br />of desiccation. <br />Fauna of Hubberson Gulch just above its confluence with Dry Creek (Site D-2) was dominated <br />in May by baetid mayflies and simulid larvae (Table 11-32). Streamflow at the collection <br />site was quite rapid in a relatively deep and narrow channel. The substrate appeared to <br />• <br />be coarse sand to fine gravel, providing suitable habitat for the blackfly larvae. • <br />28 <br />