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Stoneflies.
Adult insects. Nearly always found near water. Imbibing liquids only, or incapable of feeding (?). Small to medium sized; capable of flight; with two pairs of propellant wings. Head hypognathous. Mouthparts well developed to much reduced (“weak”); of the biting type (but only weakly mandibulate); not piercing; more or less conforming to the generalized biting type (having only weak or vestigial mandibles, but well developed maxillae complete with galea, lacinia and 5-segmented palps, and a complete labium with 3-segmented palps). Antennae conspicuous; simple; 15–35 segmented (long, setaceous, filiform, “many-segmented”). Ocelli 2, or 3. Wings four; of similar texture in both pairs (differing in this respect from other orthopteroid Orders). Fore-wings membranous. Hind-wings larger than the fore-wings (often much larger); markedly broader than the fore-wings; folded in repose (their anal lobes folding fan-wise against the body, and the hand-wings overlain by the fore-wings, of which one closely enwraps all but the base of the other). Wings with numerous cross-veins (often), or with few cross-veins; more or less naked. Wings of the resting insect closed and directed backwards; not held roof-like. Tarsi 3 segmented. Abdomen conspicuously appendaged at the rear (with two thread-like cerci, and usually a pair of large paraprocts, which are often fused with the bases of the cerci and are frequently armed with copulatory hooks); with long terminal bristles, or not spectacularly appendaged; with cerci clearly visible at its tip. Abdomen of females generally with no exserted ovipositor. Abdomen apparently 10 segmented.
Larvae. Larvae aquatic (with or without external gills. Distinguishable from nymphs of Ephemeroptera by their large prothorax and absence of an appendix dorsalis); 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. Capniidae, Chloroperlidae, Leuctridae, Nemouridae, Perlidae, Perlodidae, Taeniopterygidae; genera 16; 34 species.
General comments. A small orthopteroid Order of soft-bodied, weak-flying insects with membranous wings and aquatic nymphs, frequenting habitats with unpolluted, moving water. The larger species are popular as trout bait.
Illustrations. • Dinocras cephalotes (Curtis): Perlidae. Broad-headed Stone-fly; B. Ent. 190). • Dinocras cephalotes (detail, B. Ent. 190). • Dinocras cephalotes (dissection details, B. Ent. 190). • Dinocras cephalotes (B. Ent. 190, legend+text). This contains what appears to be Curtis's original species description. • Dinocras cephalotes (B. Ent. 190, text cont.). • 2, Nemoura cinerea (Nemouridae); 3, Leuctria geniculata (Leuctridae); 4, Isogenus nubecula (Perlodidae): Stephens v10, 1835.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, 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. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: orders. Version: 14th April 2022. delta-intkey.com’.
