Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


Wasps'-nest beetles.

General appearance. 10–12 mm long. Body length/maximum body width 2.25–4.75. Elytral length/pronotal length 0.9–5. 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 (and tapered); dorsally strongly convex (humped); asymmetrically humped, and tapered to the rear; conspicuously necked, or not necked; not waisted to somewhat waisted; brown or black, sometimes patterned with a yellow or brown and black markings; exhibiting bright ‘warning colours’, or without ‘warning colouration’. 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 strong. Eyes strongly protuberant, or not strongly protuberant; bristly, or without bristles. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles without a mola. The mandibular apices simple. The incisor edges of the mandibles simple. 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 short; 2–4 segmented, or (9–)11 segmented. Antennal scape not swollen. Antennae pectinate, or plumose or biplumose. Antennal insertions visible from above, or hidden from above; not in fossae.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.25–1.42. The pronotum without lateral keels. Prothorax without notopleural sutures. Scutellum absent. The prosternal process complete; falling short of the mesoventrite to slightly overlapping the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities open behind externally; broadly open; narrowly separated; strongly transverse to slightly transverse; without lateral extensions; internally closed by a slender bar. The mid-leg coxae countersunk in ‘mesocoxal cavities’; separated by less than the shortest diameter of the cavity. The mid-leg coxal cavities narrowly separated, or moderately to widely separated; not or scarcely oblique, or markedly oblique; open laterally. Hind-leg coxae contiguous or narrowly separated; not markedly extended laterally; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 4. 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, or one-toothed or bifid, or serrate, denticulate or pectinate; with an empodium between them (this sometimes with three or more setae), or without an associated empodium. Hind tarsi with one segment fewer than the mid-tarsi; 4-segmented.

Elytra present. Elytral length/maximum width across the elytra 0.55–3.3. Elytra individually distinctly tapered to their apices; not meeting along the full length of the mid-line; short, exposing several terminal abdominal tergites; exposing at least three complete abdominal tergites; not truncate. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed, or absent or much reduced; fringed with long hairs on the hind margin, or not fringed. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 5–9; all articulated and moveable. Abdominal segment 8 apparently without functional spiracles. The male external genitalia tenebrionoid, or not classified.

Adult habitat, ecology. Predacious, or not predacious (?); free living, on living vegetation and associated with flowers.

Larvae. Mature larvae small to medium-sized. The larvae elongate and more or less parallel-sided. Body circular in cross-section, or somewhat flattened, or strongly flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 1 segmented. Stemmata absent. 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 1 segmented. The labium without ligula between the palps. Labial palps absent or non-segmented. Mesothoracic legs present and segmented; 4 segmented, or 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 annular); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae in wasps' nests; (endo-) parasitic (on wasp larvae).

This description of the larva refers to late instar. The first instar (triangulin) larva has 5 stemmata on either side of the head, 3-segmented antennae, 3-segmented maxillary palps, and may exhibit spiracular tubes on abdominal segment 8.

Classification. Suborder Polyphaga; Infraorder Cucujiformia; Superfamily Tenebrionoidea.

Representation in Britain and Ireland, and worldwide. About 450 species worldwide. 1 species in Britain (M. paradoxus (Wasps' Nest Beetle)); genera in Britain 1; Metoecus.

General comments. The beetles humped and tapered, with deflexed head.

Illustrations. • Metoecus paradoxus (Wasps'-nest beetle: B. Ent. 019). • Metoecus paradoxus (details, B. Ent. 019). • Metoecus paradoxus: B. Ent. 019, legend+text. • Metoecus paradoxus: B. Ent. 019, text cont.. • Metoecus paradoxus, with Anthicidae and Anaspis: Fowler 5, 150 (1891). • Fowler 5, 150 (1891): original legend.. • Metoecus paradoxus (Rye & Fowler X6).

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.’.