Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz



Hide beetles.

General appearance. 5–10 mm long. Body length/maximum body width 1.55–1.95. Elytral length/pronotal length 2–3.2. Base of prothorax not or scarcely narrower than the combined elytral bases, or distinctly narrower than the combined elytral bases. Greatest prothoracic width not narrower or only slightly narrower than the greatest elytral width. Beetles oval to elongate-oval; dorsally somewhat convex to dorsally strongly convex; not necked; somewhat waisted to conspicuously waisted. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; exhibiting scales or scale-like setae, or with neither scales nor scale-like setae.

Detailed morphology. Beetles not prognathous. The head not covered by the thorax. Inclination of the head strong to very strong (the head deflexed and the mouthparts concealed to the extent that the mandibles are not visible from above). Eyes not each divided into upper and lower halves, strongly protuberant, or not strongly protuberant; without bristles; finely facetted. The labrum concealed beneath the clypeus; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola, or with a reduced mola. The mandibular apices simple. The incisor edges of the mandibles with a single tooth. The maxillae with distinct galea and lacinia apically to the palp. The apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae very short; strongly asymmetric; not elbowed; 9 segmented (cf. Jessop), or 10 segmented; clubbed. Antennal clubs tightly lamellate (but with the capacity to open fan-like). Antennal insertions hidden from above; not in fossae.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.55–0.85. 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 narrowly rounded or acute, or broadly rounded or obtusely angulate. The prosternal process interrupted, or entire; when not interrupted, complete; slightly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities closed behind externally; broadly closed; medianly confluent, or narrowly separated; strongly transverse, or slightly transverse; without lateral extensions; internally open. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity. The mid-leg coxal cavities contiguous; not or scarcely oblique; closed laterally. Hind-leg coxae contiguous or narrowly separated; extending laterally to meet the elytra. Tarsal segmentation formula 5, 5, 5. The tarsi without bilobed segments; without ‘hidden’ segments. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pentamerous; the penultimate segment not distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; usually without an associated empodium (or this very inconspicuous and not setose). Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytral length/maximum width across the elytra 1.1–1.32. Elytra meeting along the length of the mid-line; covering most to all of the abdomen (the pygidium concealed); exposing no more than part of the terminal tergite. The pygidium entirely concealed by the ends of the elytra even when viewed from behind. Elytra dull; rough, or tuberculate, or ribbed (heavily sculptured). 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. Elytra with epipleura. Elytral epipleura broad, reaching to the tips of the elytra. Wings well developed, or absent or much reduced. Wings with an anal lobe. Wings without a medial fleck. Abdominal sternites 5; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles. The male external genitalia trilobate.

Adult habitat, ecology. Not predacious; associated with carrion and on shed fur or feathers (in dry carrion, old bones and in birds’ nests); necrophagous and feeding on dried animal remains (towards the end of the succession of insects invading carcasses, being mostly associated with dry animal material including bones).

Larvae. Mature larvae small to medium-sized. The larvae elongate and more or less parallel-sided; C-shaped in lateral view. Body circular in cross-section. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata absent. The frontoclypeal suture between frons and clypeus indistinct or absent, or distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth, or bilobed or bidentate. The maxillary palps 4 segmented. The labium with a short ligula between the palps. Labial palps present and segmented; 2 segmented. Mesothoracic legs present and segmented; 5 segmented; the tarsi 1-clawed (the tarsal claws long and acute, unlike those of Geotrupidae and Scarabaeidae); with 1 moveable claw. Visible abdominal segments 10. Tergum 9 of the abdomen entirely dorsal. The abdomen having functional spiracles on anterior segments (these biforous, bilabiate or cribriform); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae in carrion, or in shed fur or feathers (or rather, in vertical burrows in the soil under the food source); necrophagous, or feeding on dried animal remains (primarily consuming dried skin and hair).

The larvae curved, with three pairs of well-developed legs with prominent claws, not stridulating.

Classification. Suborder Polyphaga; Infraorder Scarabaeiformia; Superfamily Scarabaeoidea.

Representation in Britain and Ireland, and worldwide. About 300 species worldwide; genera 3. 3 species in Britain (T. perlatus, T. sabulosus, T. scaber); genera in Britain 1; Trox. E.g., T. sabulosus (Sand-loving Trox).

General comments. Beetles dorsally heavily sculptured and dull black, sometimes with tufts of setae, often stridulating by rubbing the edges of abdominal segments against the internal margins of the elytra..

Illustrations. • Trox sabulosus (Sand-loving Trox: B. Ent. 574). • Trox sabulosus (dissection details, B. Ent. 574). • Trox sabulosus (adult beetle, enlarged: B. Ent. 574). • Trox sabulosus: B. Ent. 574, legend+text. • Trox sabulosus: B. Ent. 574, text (cont.). • Trox sabulosus and Trox scaber, with Scarabaeidae and Geotrupidae: Fowler 4, 102 (1890). • Fowler 5, 102 (1890): original legend..

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.’.