Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz



Net-winged Beetles.

General appearance. 5–9 mm long. Body length/maximum body width 1.1–4.5. Elytral length/pronotal length 2.4–11.73. Base of prothorax not or scarcely narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width, or distinctly narrower than greatest elytral width. Beetles elongate; not necked; somewhat waisted; usually red (or reddish yellow) and black; exhibiting bright ‘warning colours’. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Inclination of the head slight to very strong. Eyes strongly protuberant; without bristles. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles present, or absent or vestigial; when present without a mola. The mandibular apices when mandibulate, simple. The incisor edges of the mandibles simple. The maxillae with distinct galea and lacinia apically to the palp, or with a single apical structure additional to the palp. The apical segment of the maxillary palps cylindrical to fusiform, or somewhat expanded and truncate to subtriangular, or securiform to cultriform. The apical segment of the labial palps more or less expanded apically, or not expanded apically. Antennae short to longer than the insect's head to tail length; 9–11 segmented. Antennal scape not swollen. Antennae filiform (flattened), or clubbed, or serrate, or pectinate. Antennal clubs 2 segmented. Antennal insertions visible from above; not in fossae.

Cervical sclerites present. Prothorax shorter than wide to about as long as wide. Pronotal length/maximum pronotal width 0.43–0.76. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest markedly narrower than the adjoining part of the abdomen, or not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; not elevated; anteriorly simple; posteriorly broadly rounded or obtusely angulate, or truncate, or emarginate. Metaventrite without a transverse groove. The fore-leg coxae attached externally, in the absence of procoxal cavities. The mid-leg coxae attached externally, in the absence of mesocoxal cavities. Hind-leg coxae contiguous or narrowly separated; extending laterally to meet the elytra; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 3-segmented (or fewer), or 5-segmented. Mid-leg tarsi 3-segmented (or fewer), or 5-segmented; pentamerous, or with fewer than three segments; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged (but sometimes with basal setae). The claws of the mid-leg tarsi simple, or one-toothed or bifid; with an empodium between them (this with no more than two setae), or without an associated empodium. Hind tarsi with as many segments as the mid-tarsi; 3-segmented (or fewer), or 5-segmented.

Elytra present (but dehicent). Elytral length/maximum width across the elytra 0.9–3.75. Elytra meeting along the length of the mid-line, or not meeting along the full length of the mid-line (usually widened apically); covering most to all of the abdomen; exposing no more than part of the terminal tergite, or at least three complete abdominal tergites; soft; ribbed (4-ribbed). Elytra with six or more longitudinal lines of punctures, or apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae; the lines per elytron when more than five, 10. Scutellary striole absent. Wings well developed, or absent or much reduced. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 7–8, or 10; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles. The male external genitalia trilobate, or not classified.

Adult habitat, ecology. On living vegetation, or associated with flowers (commonly on Umbelliferae), or under bark (or in the soil); adults feeding on nectar, or some probably not at all.

Larvae. Mature larvae small to medium-sized. The larvae elongate and more or less parallel-sided. Body somewhat flattened to strongly flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized; ventrally more or less heavily pigmented, or ventrally only very lightly pigmented. The antennae 2 segmented. Stemmata present; on either side of the larval head 1. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 4 segmented. The labium without ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen extending to the underside. The abdomen having functional spiracles on anterior segments (these biforous or bilabiate); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci, or without cerci.

Larvae in decaying plant material and under bark; consuming decaying plant material, or consuming decaying plant material and mycetophagous (perhaps eating slime moulds and yeasts).

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Cantharoidea.

Representation in Britain and Ireland, and worldwide. Genera about 50. 4 species in Britain; genera in Britain 3; Dictyoptera, Platycis, Pyropterus. E.g., D. aurora; P. minutus (Black-neck Lycus).

General comments. These beetles are very distasteful to predators, and serve as models for numerous insect mimics. They have characteristic soft integument, flattened form and narrow, dehiscent elytra which are commonly coloured in combinations of reddish or yellowish and black; and in common with Cantharidae, Lymexylidae, Lampyridae, Meloidae, some Dermestidae, some Melyridae and some Staphylinidae, their undersides lack the usual procoxal cavities..

Illustrations. • Platycis minutus (Black-necked Lycus: B. Ent. 263). • Platycis minutus (details, B. Ent. 263). • Platycis minutus: B. Ent. 263, legend+text. • Platycis minutus: B. Ent. 263, text cont.. • Dictyoptera aurora (as Eros), Pryopterus nigroruber (as affinis), Platycis minutus (with Scirtidae and Psephenidae): Fowler 4, 110 (1890). • Fowler 4, 110 (1890): original legend.. • Dictyoptera aurora (Rye & Fowler IX2).

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: the families of Coleoptera. Version: 16th May 2016.’.