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• The body is oval and flattened.
• The head is concealed from above by the pronotum.
• Tympana and stridulating organs (usually) are absent.
• Wings are generally present, though in some species they are much reduced.
• The females of many species have shorter wings than the males.
• The cerci are one- to many-segmented and usually fairly long.
• The antennae are long and filiform.

• 1. Length 3 mm or less; found in ant nests (Attaphila, Myrmecoblatta)..........Polyphagidae*
• 1'. Length over 3 mm; almost never found in ant nests..........2
• 2(1'). Middle and hind femora with numerous spines on ventroposterior margin..........3
• 2'. Middle and hind femora without spines on ventroposterior margin, or with hairs and bristles only, or 1 or 2 apical spines..........7
• 3(2). Pronotum and front wings densely covered with silky pubescence; length 27 mm or more (tropical species accidental in the United States)(Nyctibora)..........Blattellidae*
• 3'. Pronotum and front wings glabrous or only very sparsely pubescent..........4
• 4(3'). Ventroposterior margin of front femora with row of spines that either decrease gradually in size and length distally or are nearly equal in length throughout..........5
• 4'. Ventroposterior margin of front femora with row of heavy spines proximally and more slender and shorter spines distally..........6
• 5(4). Female subgenital plate divided longitudinally; male styli similar, slender, elongate, and straight; length 18 mm or more (Blatta, Periplaneta, Eurycotis, Neostylopyga)..........Blattidae
• 5'. Female subgenital plate entire, not divided longitudinally; male styli variable, often modified, asymmetrical, or unequal in size; length variable, but usually less than 18 mm (Supella, Cariblatta, Symploce, Pseudomops, Blattella)..........Blattellidae
• 6(4'). Front femora with only 1 apical spine; supra-anal plate weakly bilobed; color glossy light brown, with sides and front of pronotum and basal costal part of front wings yellowish; 15-20 mm in length; Florida Keys (Phoetalia, Epilampra)..........Blaberidae*
• 6" Front femora with 2 or 3 apical spines; supra-anal plate not bilobed; size and color variable; widely distributed (Ectobius, Latiblatella, Ischnoptera, Parcoblatta, Euthlastoblatta, Aglaopteryx)..........Blattellidae
• 7(2'). Distal portion of abdomen (usually including cerci) covered by produced seventh dorsal and sixth ventral abdominaal sclerites, subgenital plate absent; wingless, body almost parallel-sided, shining reddish brown, finely punctate, 23-29 mm in length; widely distributed, usually found in rotting logs..........Cryptocercidae*
• 7'. Distal portion of abdomen not so covered, subgenital plate present; wings usually well developed (absent in some females); usually oval in shape; size and color variable; mostly southern United States..........8*
• 8(7'). Hind wings with an apical portion (intercalated triangle or appendicular area) that folds over when wings are in resting position; 8.5 mm in length or less, and glossy yellowish in color, often beetlelike in appearance; southeastern United States (Chorisoneura, Plectoptera)..........Blattellidae*
• 8'. Hing wings not as above..........9*
• 9(8'). Front femora with 1 to 3 spines on ventrposterior margin and 1 at tip; length over 40 mm; arolia present; southern Florida (Blaberus, Hemiblabera..........Blaberidae*
• 9'. Front femora without spines on ventroposterior margin and with 1 or a few at tip; size variable; arolia present or absent; eastern and southern United States..........10*
• 10(9'). Wings well developed, the anal area of hind wings folded fanwise at rest; fons flat, not bulging; length over 16 mm, or pale green in color (Panchlora, Pycnoscelus, Nauphoeta, Leucophaea)..........Blaberidae*
• 10'. Anal area of hind wings flat, not folded fanwise at rest (some females are wingless); frons thickened and somewhat bulging; usually (except some Arenivaga) less than 16 mm in length and never green (Holocompsa, Eremoblatta, Compsodes, Arenivaga)........Polyphagidae*

Most nymphs and some soft-bodied adult specimens should be preserved in alcohol, but most adults can be pinned. The pin should be placed through the right tegmen, in about the middle (from front to rear) of the body. If the specimen is very soft-bodied, the body should be supported by a piece of cardboard or by pins; otherwise, it will sag at either end.

Acknowledgements Casandra Lloyd and Sara Serji, University of Georgia, Athens.