Insects of Britain and Ireland: the families of Coleoptera
General appearance. 1.5–3 mm long. Body length/maximum body width 1.15–1.93. Elytral length/pronotal length 2.6–3.85. 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 broadly oval; terrapin-like in shape, with flattened and clear margins to thorax and elytra; dorsally dorsally strongly convex (but flat beneath); not necked; not waisted; decidedly short-legged. Upper surfaces of body glabrous or subglabrous; not bristly; with neither scales nor scale-like setae.
Detailed morphology. Beetles not prognathous. Eyes not strongly protuberant; without bristles. The labrum at least partly visible in antero-dorsal view; labrum 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; 11 segmented; without a much-elongated scape. Antennal scape swollen (enlarged and triangular). Antennae clubbed. Antennal clubs 3 segmented. Antennal insertions visible from above, or hidden from above.
Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.26–0.5. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly broadly rounded or obtusely angulate. The prosternal process complete; slightly overlapping the mesoventrite to moderately or strongly overlapping the mesoventrite, or concealing most or all of 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, or quite widely separated; circular to longer than wide; with narrow lateral extensions, or without lateral extensions; internally closed by a slender bar. The mid-leg coxae countersunk in mesocoxal cavities; separated by more than the shortest diameter of the cavity. The mid-leg coxal cavities moderately to widely separated; not or scarcely oblique; closed laterally. Hind-leg coxae contiguous or narrowly separated; not markedly extended laterally; not shaped posteriorly to receive the femur. Tarsal segmentation formula 4, 4, 4. The tarsi exhibiting bilobed segments; with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth, or without hidden segments (segment four greatly reduced, the first three broad and lobed below). 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 tetramerous; 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 one-toothed or bifid (appendiculate, or with a basal tooth). Hind tarsi with as many segments as the mid-tarsi, or with one segment fewer than the mid-tarsi; 4-segmented, or 5-segmented.
Elytral length/maximum width across the elytra 0.9–1.5. Elytra exposing no more than part of the terminal tergite; hard; very glossy; glabrous; striate, or without striae (but usually with distinct sutural striae towards the rear). Elytra with six or more longitudinal lines of punctures, or with six or more impressed striae, 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, 6–7, or 8 to 9. Scutellary striole absent. 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. Wings without a medial fleck. Abdominal sternites 5; all articulated and moveable. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform, or tenebrionoid.
Adult habitat, ecology. On living vegetation, associated with fungi, and associated with flowers (commonly in those of Compositae); phytophagous and mycetophagous (favouring pollen and smuts).
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 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 only very lightly pigmented. The antennae 3 segmented. Stemmata present; on either side of the larval head 6. The frontoclypeal suture between frons and clypeus indistinct or absent, or distinct. 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. The maxillary palps 3 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 9. Tergum 9 of the abdomen extending to the underside. The abdomen having functional spiracles on anterior segments (these annular, annular-uniforous or annular-biforous); with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes (on segments 1 and 8), or without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci.
Larvae commonly in living vegetation and associated with flowers; phytophagous and mycetophagous (e.g., in heads of Compositae, eating pollen and smuts).
The larvae rather onisciform, whitish, with 3-segmented antennae, 2 to 5 pairs of ocelli on each side and well developed legs; abdomen 9-segmented.
Classification. Suborder Polyphaga; Superfamily Cucujoidea.
Representation in Britain and Ireland, and worldwide. About 640 species worldwide; genera about 50. 16 species in Britain; genera in Britain 3; Olibrus, Phalacrus, Stilbus.
General comments. Very small, broadly oval and strongly convex beetles, the surface glabrous and polished.
Illustrations. • Olibrus aeneus, Phalacrus corruscus, Stilbus testaceus (with Coccinellidae): Fowler 3, 81 (1889). • Fowler 3, 81 (1889): original legend.. • Olibrus flavicornis (with Coccinellidae, Pselaphidae, etc.): Fowler Suppl. 12, 1913. • Fowler Suppl. 12, 1913: original legend.. • Olibrus, Phalacrus, Stilbus (from Joy).
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’.