Insects of Britain and Ireland: the families of Coleoptera
Flat grain beetles.
General appearance. 2.3–4.5 mm long. Body length/maximum body width 1.5–5.55. Elytral length/pronotal length 1.8–3.95. 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, or distinctly narrower than greatest elytral width. Beetles elongate; dorsally flattened to dorsally somewhat convex (convex beneath); conspicuously necked to not necked; conspicuously waisted; yellowish or reddish brown. Upper surfaces of body glabrous or subglabrous, or non-glabrous; exhibiting stiff, erect, dark bristles, or not bristly; with neither scales nor scale-like setae.
Detailed morphology. Beetles prognathous. Eyes strongly protuberant, or not strongly protuberant; bristly, or without bristles. The labrum at least partly visible in antero-dorsal view, or concealed beneath the clypeus (some Silvaninae); labrum when recorded, mostly moderately to heavily sclerotized. Mandibles with a well developed mola. The mandibular apices bidentate or bilobed. The incisor edges of the mandibles simple, or 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 short to long, but not exceeding the insects head to tail length; (9–)11 segmented. Antennal scape not swollen. Antennae clubbed, or gradually expanding towards the apex (i.e., sometimes only weakly clubbed). Antennal clubs 3 segmented. Antennal insertions visible from above, or hidden from above.
Cervical sclerites present (Silvaninae), or absent (Brontinae). Prothorax longer than wide. Pronotal length/maximum pronotal width 0.6–2.65. The pronotum variously with lateral keels (pronotal carinae), or without lateral keels; keels when present, complete, or incomplete. Prothorax at its widest markedly narrower than the adjoining part of the abdomen, or not markedly narrower than the adjoining part of the abdomen; having the front corners produced, or with serrated sides. Prothorax without notopleural sutures. Scutellum conspicuous; elevated above the mesoscutum in lateral view, or not elevated; anteriorly simple; posteriorly broadly rounded or obtusely angulate, or truncate. The prosternal process complete; 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 (Brontinae), or closed behind externally; broadly open to narrowly open, or broadly closed; quite widely separated; circular to longer than wide; without lateral extensions; internally open. The mid-leg coxae countersunk in mesocoxal cavities; separated by less than the shortest diameter of the cavity, or more than the shortest diameter of the cavity. The mid-leg coxal cavities narrowly separated, or moderately to widely separated; not or scarcely oblique; open laterally. Hind-leg coxae contiguous or narrowly separated, or widely separated; not markedly extended laterally; not shaped posteriorly to receive the femur. Tarsal segmentation formula 4, 4, 4. The tarsi exhibiting bilobed segments (third segment lobed below); with a tiny basal segment that is hard to detect, or without hidden segments. Front tarsi with as many segments as the mid-tarsi; 4-segmented, or 5-segmented. Mid-leg tarsi 4-segmented, or 5-segmented; pentamerous, or pseudotetramerous (the penultimate one), or tetramerous; the penultimate segment variously not distinctly shorter than the antepenultimate one, or distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple. Hind tarsi with as many segments as the mid-tarsi; 4-segmented, or 5-segmented.
Elytral length/maximum width across the elytra 1.15–3.5. Elytra not individually tapered; covering most to all of the abdomen; exposing no more than part of the terminal tergite. Elytra with six or more longitudinal lines of punctures; the lines per elytron 6–7, or 8 to 10. Scutellary striole present, or absent (some Silvaninae). Elytra with epipleura. Elytral epipleura reaching to the tips of the elytra. Wings well developed, or absent or much reduced. Wings with an anal lobe, or without an anal lobe. Wings without a medial fleck. Abdominal sternites 5; all articulated and moveable, or comprising both fused and moveable components. Basal abdominal sternites immovably joined when present, 2. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform.
Adult habitat, ecology. Land-dwellers; on living vegetation, in decaying plant material, in dried plant material, under bark, and in stored plant products (some being pests of stored cereals); mainly consuming decaying plant material and mycetophagous, or eating dried plant material or stored plant products.
Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae elongate and more or less parallel-sided. Body somewhat flattened, or somewhat flattened to strongly flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized, or dorsally only very lightly pigmented or sclerotized; ventrally more or less heavily pigmented, or ventrally only very lightly pigmented. The antennae 2 segmented, or 3 segmented. Stemmata present; on either side of the larval head 6. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule separated by a complete suture, or partly fused, with an incomplete suture. Apices of the mandibles bilobed or bidentate, or trilobed or tridentate, or multilobed or multidentate. The maxillary palps 3 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 entirely dorsal. The abdomen having functional spiracles on anterior segments (these annular); with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes (Brontinae, Cryptamorpha), or without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci (Brontinae, Cryptamorpha), or without cerci.
Larvae in living vegetation, in decaying plant material, in dried plant material, under bark, and in stored plant products (some being pests of stored cereals).
Classification. Suborder Polyphaga; Superfamily Cucujoidea.
Representation in Britain and Ireland, and worldwide. About 500 species worldwide; genera about 60. 10 species in Britain; genera in Britain 8; Ahasverus, Cathartus, Cryptamorpha, Nausibius, Oryzaephilus, Psammoecus, Silvanoprus, Silvanus.
General comments. Beetles minute, elongate, flattened yellowish or reddish brown.
Illustrations. • Biphyllus (from Joy). • Oryzaephilus mercator, with unrelated taxa: Fowler 6, 14 (1913). • Fowler 6, 14 (1913): original legend.. • Ahasverus, Nausibius, Oryzaephilus, Psammoechus, Silvanoprus (with Cucujidae etc.): Fowler 3, 93 (1889). • Fowler 3, 93 (1889): 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. delta-intkey.com’.