Insects of Britain and Ireland: orders

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L. Watson and M. J. Dallwitz


Book-lice, Psocids.

Adult insects. Phytophagous, or saprophagous, or consuming stored produce, or mycophagous. Minute to small; capable of flight, or flightless (not uncommonly); when wings developed with two pairs of propellant wings. Body dorsiventrally flattened to laterally flattened (?). Head hypognathous. Mouthparts well developed; of the biting type; not piercing; conforming to the generalized biting type to highly modified (the mandibles asymmetric, the maxillary lacinia modified into an elongate, strongly sclerotized rod sunken well into the head capsule and apically variously toothed, the labial palpi reduced). The clypeus divided into a narrow, transverse anteclypeus and a characteristically bulbous postclypeous. Antennae conspicuous; simple; 15–35 segmented (‘many-segmented’). Ocelli 3 (in winged forms), or 0 (in apterous forms). Wings when present, four; of similar texture in both pairs. Fore-wings membranous. Hind-wings smaller than the fore-wings; no broader than the fore-wings. Wings with few cross-veins (venation reduced); more or less naked. Wings of the resting insect closed and directed backwards; usually held roof-like over the abdomen. The body and legs of wingless adults without scales. Tarsi 2 segmented, or 3 segmented. Abdomen not conspicuously appendaged; lacking clearly visible cerci; apparently 9 segmented.

Larvae. Larvae with three pairs of segmented thoracic legs; without ventral abdominal prolegs. Development of larva into adult gradual; exopterygote; not involving a pupal stage.

Classification. Subclass Pterygota; Division Exopterygota.

British representation. 11 families; genera about 50; about 90 species.

Special features. The wingless adults not larviform, with only obscure thoracic segmentation.

General comments. Adults free living, feeding on plants, plant and animal remains, fungal hyphae, stored products, etc. Of little economic significance.

Illustrations. • Caecilius fuscopterus (as Psocus fenestratus Curtis), B. Ent. 648. • Caecilius fuscopterus: B. Ent. 648, legend+text. • Caecilius fuscopterus: B. Ent. 648, text cont.. • Peripsocus phaeopterus, adult and nymph: Imms, 1957. Peripsocus phaeopterus. Adult. Young nymph.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: orders. Version: 16th May 2016.’.