The Thysanoptera comprises a single order in which the members differ from all other insects in the form of the mouth parts and also of the tarsal arolium. The mouth parts are asymmetric, with only the left mandible functional in larvae and adults, the right being resorbed in the embryo. The two maxillary stylets are co-adapted to form a single tube through which salivary secretions are pumped out into a plant and partially digested cell contents are pumped back into the thrips foregut (Chisholm & Lewis, 1984; Heming, 1993). The feeding apparatus thus differs fundamentally from the feeding stylets of Hemiptera such as aphids and coccids. Larval thrips retain tarsal claws, but these are replaced in adults by an inflatable arolium (Heming, 1971) that functions in a similar way to that of dipterous flies.
Worldwide, about 6040 species of Thysanoptera are recognized currently, in nearly 825 genera (Mound, 2012). Two sub-orders are recognized, the Terebrantia and the Tubulifera. Eight families are recognized in the Terebrantia, plus a further five families known only from fossils, but only one family in the Tubulifera. The thrips fauna of California is remarkable in that eight of the nine extant families are represented here. In a contrasting classification, Bhatti (1994, 2006) has divided the Thysanoptera into two separate Orders and recognized about 40 families; that system is mainly about the levels at which groups should be classified, rather than about their relationships (Mound & Morris, 2007). A summary of the available family-level classifications is presented in Mound (2011a).