This genus is significant all year long but is especially important from midsummer to late fall when the larger flies are scarce. Baetis is represented in all sections of the country by a great number of species, all small in size, varying from 4 to 10 mm in length. Nymphs are highly streamlined with long, slender legs and single platelike gills on segments 1 to 7. Some species have only two tails, but most have three, with the middle one distinctly shorter. Adults have paired marginal veinlets in the fore wing, tiny hind wings with a hooklike projection on the front edge, and two tails. Eyes of the male are turbinate.