Insects of Britain and Ireland: orders

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L. Watson and M. J. Dallwitz



Adult insects. Nearly always found near water. Imbibing nectar (or water only - the mouth-parts always being reduced), or incapable of feeding; voluntarily emitting sound, or mute. Small to medium sized; with hardened ‘elytra’ (q.v.), representing the fore-wings, or without elytra; capable of flight; with two pairs of propellant wings. Head hypognathous. Mouthparts much reduced (all but the palps being very reduced and specialised for ingesting liquids, the mandibles vestigial); functional for feeding to non-functional for feeding; if operational for feeding, suctorial; not piercing. Antennae conspicuous (very long and filamentous); simple; 15–35 segmented (‘many-segmented’). Ocelli 0 (e.g., Leptoceridae), or 2 (in some Hydroptilidae), or 3 (usually, when present. Many adult Trichoptera are nocturnal and are attracted to light, but some fly actively in sunlight, and it would be worth pursuing the extent to which variation re ocelli is associated with this). Wings four; of similar texture in both pairs to markedly differently textured in the two pairs (the fore-wings somewhat leathery, the hind-wings thinner). Fore-wings membranous to leathery; with a pterostigma (in Rhyacophilidae), or without a pterostigma (mostly not clearly developed). Hind-wings smaller than the fore-wings to larger than the fore-wings; markedly broader than the fore-wings, or no broader than the fore-wings; folded in repose, or not folded in the resting insect. Wings with few cross-veins; conspicuously hairy (though occasionally also with some narrow scales); exhibiting ‘corneous dots’; fringed (always?). Wings of the resting insect closed and directed backwards; held roof-like over the abdomen (though nearly flat in Hydroptilidae). Tarsi 5 segmented. Abdomen conspicuously appendaged at the rear, or not conspicuously appendaged; exhibiting a conspicuous ovipositor, or not spectacularly appendaged; with cerci clearly visible at its tip (short, one-segmented), or lacking clearly visible cerci. Abdomen of females with an exserted ovipositor (in some families), or with no exserted ovipositor. Abdomen apparently 9 segmented (males, the tenth being incorporated in the terminalia), or 10 segmented (in females, but sternum 1 not differentiated).

Larvae. Larvae aquatic (often case-making; without spiracles, but often with tracheal gills, otherwise gaseous exchange occurs via the general body surface); feeding in the open (commonly constructing characteristic cases which they carry around with them, comprising an inner, silken tube with affixed fragments of wood, plant stems and stones); predatory (then sometimes making elaborate silken nets or traps for enmashing prey), or phytophagous, or saprophagous (more or less omnivorous as a group, with the case-bearing forms generally vegetarian and the free forms predatory); with three pairs of segmented thoracic legs; without ventral abdominal prolegs; with paired anal prolegs. The abdominal prolegs bearing crochets (the terminal prolegs usually bearing hooks anchoring the larva to its case or substrate), or without crochets. Larval head with a well sclerotized capsule. Development of larva into adult involving marked metamorphosis; endopterygote; involving a pupal stage.

Pupae. Pupae without a puparium; with articulated mandibles; with free appendages.

Classification. Subclass Pterygota; Division Endopterygota.

British representation. 14 families, described individually in some detail in the accompanying data set; genera 70; 192 species.

General comments. The adult morphology resembles that of Lepidoptera, but although the wings and bodies of some Trichoptera exhibit scales, these are narrow and acuminate and never assume the broadened form characteristic of Lepidoptera; trichopteran mouthparts lack the specialised galea characteristic of Lepidoptera; caddis with ocelli usually have three, while Lepidoptera posessing them have ony two, and a further distinction is that the wings of Lepidoptera lack ‘corneous spots’..

Illustrations. • Agrypnia pagetana Curtis (Yarmouth Grannom, Caddis-fly: B. Ent. 540). For numerous images of Trichoptera, see the ‘Families of British Trichoptera’ data set. • Agrypnia pagetana (B. Ent. 540, legend+text). • Agrypnia pagetana (B. Ent. 540, legend cont.). • Chimarra marginata (Marginated Caddis-fly: B. Ent. 561). • Chimarra marginata (B. Ent. 561, legend+text). • Chimarra marginata : B. Ent. 561, text cont.). • Limnephilus elegans Curtis (Elegant Grannom, Caddis-fly: B. Ent. 488). • Limnephilus elegans (B. Ent. 488, legend+text). • Limnephilus elegans (B. Ent. 488, text cont.). • Oecetis ochracea Curtis (Ochre Caddis-fly: B. Ent. 057). • Oecetis ochracea (B. Ent. 57, legend+text). • Oecetis ochracea (B. Ent. 57, text cont.). • Polycentropus Curtis, Crunoecia irrorata (Curtis): (Many-spotted Caddis-fly; B. Ent. 544. • Crunoecia irrorata (detail, B. Ent. 544). • Crunoecia irrorata (dissection details, B. Ent. 544). • Crunoecia irrorata (B. Ent. 544, legend+text). • Crunoecia irrorata (B. Ent. 544, text cont.).

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.’.