This hatch begins in Pennsylvania and the Catskills in the middle of May. It peaks there in late May and early June. Throughout the rest of June and early July the hatch moves into the Adirondacks, New England, and the Upper Midwest.
The best action lasts from 1-3 weeks in most places. The traditional March Brown duns originally in the vicarium species are more common toward the beginning of the hatch, while the former-fuscom Gray Fox variety take over in the latter weeks.