Isonychia nymphs are good swimmers, and live in fast moving riffles. Isonychia are easy to recognize because of their dark gray color, and white stripe running down the middle of their wing case. Before hatching they migrate to the edge of the stream, or rocks protruding the streams surface, where they crawl up out of the water and shed their husk. Once they begin hatching empty husks will be in abundance along the streams edge. On big water like the Upper Delaware Isonychia will hatch from the surface like most other Mayflies, but a good number of nymphs can still be found along the streams edge. Isonychia bicolor duns earned the common name White Gloved Howdy because of the white color on their front legs. Hatches are heaviest in mid June and early July, but hatch sporadically through early October.