British insects: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Trogidae

~Scarabaeidae-Troginae.

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. The head not covered by the thorax. Inclination of the head slight to strong (the head deflexed and the mouthparts partly concealed). Eyes strongly protuberant, or not strongly protuberant; without bristles; finely facetted. Antennae very short; 10 segmented; clubbed. Antennal clubs lamellate. Antennal insertions hidden from above; not in fossae. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.55–0.85. 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. Metaventrite without a transverse groove. The mid-leg cavities closed laterally. Hind-leg coxae 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 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). Scutellary striole absent. Wings well developed, or absent or much reduced. Exposed abdominal sternites 5; all articulated and moveable. Abdominal segment 8 with apparently functional spiracles, or apparently without functional spiracles.

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).

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 present, or absent; on either side of the larval head when present, 1. 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; 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.

Worldwide and British representation. About 300 species worldwide; genera 3. 3 species in Britain; genera in Britain 1; Trox. E.g., T. sabulosus (Sand-loving Trox).

General comments. Beetles with dull and conspicuously sculptured or warty thorax and elytra, often stridulating by rubbing the edges of abdominal segments against 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. British insects: the families of Coleoptera. Version: 25th July 2012. http://delta-intkey.com’.

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