Most species have short fuzzy gill filaments located at the base of the legs on the underside of the thorax. Two well developed wingcases are located on top of the second and third thoracic segments. These extend slightly back over the top and side of the abdomen, covering the 10 th segment. When viewed from he top, this creates a 50-50 proportion between thorax and abdomen. The head is broad, somewhat flattened, with two well-defined eyes and long antennae.
Colors are mostly subdued browns, olives, tans, golds, and black, but multi-hued mottling is common.
Many northwest and western anglers eagerly await the hatch of big golden stones, Acroneuria pacifica and A. californica. This is usually the first big hatch of the early summer and kicks off the season with a bang. Nymph anglers, however, usually drift big imitations on the bottom and experience excellent fishing weeks, even months in advance of the hatch. Most species have a two to three-year life cycle, so large, nearly mature nymphs are availavle most of the year, and fish are usually on the lookout for them. The best nymph fishing is two to three weeks prior to the hatch when nymphs are positioning themselves close to shorelines and during the first week of the hatch when nymphs exit the water.