Both sexes either long or short winged. Body and legs blackish brown; antennal segment III variably yellow usually with apex dark;major setae and fore wing pale. Head longer than wide, cheeks parallel, eyes relatively small; postocular setae longer than dorsal length of eye, postocellar setae considerably shorter; maxillary stylets broad, retracted to eyes and close together medially in head. Antennae 8-segmented; segment III with two sensoria, IV with three sensoria; segment VIII slender and narrowed to base. Pronotum with 5 pairs of softly pointed major setae; epimeral sutures complete; basantra small, ferna transverse, mesopresternum slender medially. Fore tarsi with no tooth. Metanotum medially with weak sculpture. Fore wings parallel sided, with about 20 duplicated cilia. Pelta broad; tergites each with only one pair of sigmoid wing-retaining setae; tergite IX setae finely acute, almost as long as tube.
Males varying in size, large male with fore femora swollen, fore tarsus with prominent tooth.
Although 12 species are listed in Cryptothrips six of the older names involved cannot at present be applied to any known species. Of the other six species, three are from North America, one from Europe, and one each from Australia and New Zealand. The three species recorded from California are similar in general appearance, and currently there is no reliable distinction between them, either structural or biological. Cott (1956) illustrated C. rectangularis with the postocellar setae short, about as long as the diameter of an ocellus, and the third antennal segment is variably yellowish. There is a possibility that this species and C. sordidatus, and even C. carbonarius, all represent the same species as the northern European C. nigripes (Reuter).
Cryptothrips rectangularis Hood
Apparently breeding on dead leaves and branches.
Spores of unidentified fungi.
Apparently widespread from southern Illinois to California.