Common stonefly (Acroneuria abnormis), Newark DE. August 2017.
Most stoneflies are considered good indicators of water quality. This is in part due to their aquatic immature forms (naiads), the thoracic gills (or abdominal, depending on the taxon) that need running water to help facilitate capture of dissolved oxygen, sensitivity to temperature or size of the stream or river, and even substrate. Cold, fast-running streams or creeks tend to be a preferred habitat, and stoneflies in North America tend to be more diverse in higher latitudes.
Their immature forms are predators, although consuming dead insects or even detritus may occur at young molts. Adults do not feed. One generation occurs each year, although naiads themselves may live up to two years before emerging.