The Pheasant Tail Nymph, a British pattern tied to imitate Baetis nymphs of Britain, has become the standard Baetis pattern here, too. The addition of a bead head has made it even more effective in many cases. Before, during, and after the daily Baetis hatch, these nymph imitations will catch a lot of fish. Some trout may focus on emergers when a hatch is on. There are patterns tied to imitate this process known variously as floating nymphs, emergers, or cripples.
Cripples imitate duns that fail to escape the nymphal shuck completely and die.
In some mayfly species, Baetis included, the percentage of cripples is fairly high. But the overall number of hatching flies is much higher yet, so the species has no trouble carrying on. Where I fish Baetis hatches, it seems that dun imitations work well enough most of the time. I rarely fish emerger patterns, just dry flies to imitate duns. Baetis do ride the currents a long time before flying off, a very long time.