Key to e. US spp. by Joan Chapin (1974) (1)
4. Apical pale area occupying about one-fourth of elytral length; elongate-oval beetles; (male genitalia with basal lobe and parameres sub equal in length, ventral alae lacking) - securus Chapin
Apical pale area occupying more than two-fifths of elytral length; broadly oval beetles; (male genitalia with basal lobe longer than parameres, ventral alae present) - brullei Mulsant
5. Apical pale area of elytra occupying one-fifth of length; first abdominal sternum of male depressed at middle with minute glabrous area at posterior margin not surrounded by dense pubescence; fifth and sixth sterna with shallow fovea ••• 6
Apical pale area of elytra occupying one-third to two-fifths of length; first abdominal sternum of male unmodified; sixth deeply emarginate with two ventrally produced hooks - rubricaudus Casey
6. Basal lobe of male genitalia with large downward projecting hook on upper right ventral surface; dorsally, 2 laterally curved processes at middle of base - louisianae Chapin
Basal lobe without large downward projecting hook on upper right ventral surface; dorsally, 2 processes located each side of middle - fraternus LeConte
Scymnus brullei - e N. Amer.
Scymnus fraternus - e. US
Scymnus louisianae - se US to AZ, mostly known from: TX-LA
Scymnus rubricaudus - e US
Scymnus securus - coastal e. US
Scymnus postpinctus - w N. Amer.
Scymnus festatus Wingo - mostly AL to NY (2)
Scymnus uncus Wingo - e. US - rarely coll'ed sp. with singleton records from six e. US states.