Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.
Source: Epiproct And Dorsal Process Structure In The Allocapnia Forbesi Frison, Allocapnia Pygmaea (Burmeister), And Allocapnia Rickeri Frison Species Groups (Plecoptera: Capniidae), And Inclusion Of Allocapnia Minima (Newport) In A New Species Group
Male epiproct. Apical segment of upper limb ca. 281 µm long, and armed on the apical ca. 188 µm with dense patch of wave-like spikes (Figs. 79 - 82); apical segment ca. 106 µm wide at base, slightly constricted near mid-length, and expanded to a bluntly rounded tip. Basal segment of upper limb ca. 471 µm long and ca. 56 µm wide at mid-length; basal segment bears a wide, shallow, longitudinal groove from base to near mid-length. Greatest width of lower limb ca. 163 µm; lateral margins of lower limb bearing a sparse row of long setae near apical spoon. Male tergal process. Prominent raised bilobed structure on abdominal tergum 8 and a smaller, slightly raised process on tergum 7 (Figs. 82 - 84). Process on tergum 8 ca. 142 µm wide, covered with scale-like structures, and bearing a shallow, V-shaped notch (Fig. 83); process on tergum 7 ca. 40 µm wide, without scales or notch (Fig. 84).