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: Revision of the genus Culoptila (Trichoptera: Glossosomatidae)
Adult. Length of forewing: male 3.2 – 3.6 mm; female 3.2 mm. Color light brown; wing with nearly complete, linear whitish bar at wing anastomosis. Mesothorax of male narrow anteromesally; mesoscutal wart elongate, narrowed, rounded anteromesally; mesoscutal setae long. Mesothoracic tegulae of male rounded, greatly enlarged; tegular setae short; tegular gland large, rounded, with several pleated folds. Male genitalia. Sternum VI process short, subtruncate. Tergum IX ventral margin acutely angled, tapered from anterolateral margin, not produced posteroventrally. Inferior appendages very long, narrow apically, divergent basally, curving mesad apically. Tergum X short, about as long as wide, apex in ventral view broadly rounded to subtruncate; ventrolateral processes with apices incurved, nearly planar in caudal view, mesal margin acute; apices not or scarcely posteriorly bent. Apicodorsal projection arched, moderately elongate, apex subacute. Phallic apparatus with 2 phallic spines, phallic spines united basally, shorter spine much thickened, sinuously twisted around longer spine, with numerous, overlapping accessory spines, longer spine about 2 / 3 length of phallobase, weakly curved, apically narrowed, acuminate.