1. Dorsal hump of abdominal segment I with 4-6 rows of micro-hooks on each side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oecetis avara
Dorsal hump of abdominal segment I without micro-hooks. . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Metasternum with 2 setae; swinming hairs present on hind tibiae; hind tarsi longer than tarsal claws; case constructed of root or plant fragments placed transversly. . . . . . . . . . . . . . . . . . 3
Metasternum with more than 2 setae (except O. osteni, which may have only 2), often with row of 10 or more; swimming hairs absent on hind tibiae; hind tarsi each as sort as or shorter than its tarsal claw; case constructed of sand grains or irregularly placed plant or detrital pieces. . . 4
3. Head brown with light suscle scars; case constructed either of short twigs or roots (angled "log cabin" appearance) or thin, flat, quadrate, plant fragments; on vegetation in lakes, some slow-moving stream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oecetis cinerascens
Head yellow with dark muscle scars or pale; antennae short, reaching posterior edge of labrum; case exterior more rounded and oten curved, especially in early instars; on roots, woody debris, and vegetation in streams. . . . . . . . . . . . . . . . . . . . . . . . . .Oecetis persimilis
4. Mesonotum with pair or irregular dark areas on each side of meson; coronal suture bordered by row of 3-4 dark muscle scars on eac side; left mandible with deep crease running down from apical tooth; case constructed of sand grains. . . . . . . . . . . . . . . . . . . . . . . . . Oecetis osteni
Mesonotum without distinct pair of irregular daek areas; coronal suture bordered by 0-2 muscle scars; left mandible without crease; case constructed of plant or sand grains . . . . . . . . . . . .5
5. Head and pronotum usually with several light brown muscle scars; case constructed of sand or rock pieces wit larger ballast stones attached to sides. . . . . . . . . . . . . . . . .Oecetis nocturna
Head and pronotum pale or with various combinations of dark muscle scars, spots, or stripes; case constructed of variety of materials. . . . . . . . . Oecetis inconspicua complex**. . . . 6
6. Mesosternum with irregular patch of 80 to 100 setae; case somewhat flatened dorsoventrally, composed of sand; dorsum of hind legs dark brown; head and pronotum dark brown with sparce patterns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oecetis sp. C Floyd
Mesosternum with no more than 6 setae; case tubular, composed of sand or woody debris; dorsum of hind legs same color as rest of leg; head and pronotum dark with 50% light markings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Head with dark longitudinal stripes on middle of frontoclypeus; ventral apotome dark brown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oecetis sp. E Floyd
Head without dark longitudinal stripe on frontoclypeus; ventral apotome light brown/yellow. . 8
8. Mesonotum with no more than 4 sa3 setae; metasternum with row of 8-15 setae; head and pronotum with dark muscle scars or spots posteriorally. . . . . . . . . . . . . . Oecetis sp. F Floyd
Metanotum with 8-9 sa3 setae; metasternum with 30-36 setae; head with dark square between eyes, white "H" in the square; dark muscle scars on posterior of head; pronotum light brown with lateral freckled band across middle and dark spots posterior. . . . . . . Oecetis sp. A Floyd
* Key does not include Oecetis ditissa, O. inconspicua or O. inconspicus complex sp. G. Larvae of these species are unknown.
** The actual number of species to the Oecetis inconspicua complex is unknown. It contains at least 7 North American species of which at least Oecetis species A, F and G occur in Ohio.
Key to Species of Oecetis Nymphs*