Many adults, however, do not feed and have reduced or vestigial mouthparts. Some species are not even attracted to light. Their only importance to humans is as food for fish. Their importance as fish food has made the stonefly nymphs very well known to people who fish and aquatic ecologists. Stonefly nymphs can represent a major part of the community in clean streams.
Many species inhabit only well aerated streams.
The characteristic inability of the stoneflies, as a group, to tolerate various types of pollution has led to their increasing use as pollution indicators in environmental quality assessments, studies, etc. Where large emergences of stonefly adults blanket homes, businesses, etc. Nymphs of a few stoneflies, possibly species that are known to live in underground water, appear in wells or other drinking water supplies. Screening of intakes should eliminate such problems. Most nymphs occur under stones in well aerated streams.