Insects of Britain and Ireland: the families of Coleoptera
General appearance. 1.2–10 mm long. Body length/maximum body width 1.25–1.8. Elytral length/pronotal length 1.9–3.9. 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 short, stout, oval; dorsally strongly convex; having ventral body cavities into which the legs fold to conform with the general body surface; not necked; not waisted; decidedly short-legged (retracting the legs firmly into cavities in the ventral body surface when alarmed); dull black, or bright metallic green. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly, or exhibiting stiff, erect, dark bristles; exhibiting scales or scale-like setae, or with neither scales nor scale-like setae.
Detailed morphology. Beetles prognathous, or not prognathous. Inclination of the head slight. Eyes strongly protuberant, or not strongly protuberant; without bristles; finely facetted. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola, or with a reduced mola to without a mola; with well developed prosthecae to without prosthecae. The mandibular apices bidentate or bilobed, or multidentate or multilobed. 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, or somewhat expanded and truncate to subtriangular. The apical segment of the labial palps not expanded apically. Antennae very short to short; (10–)11 segmented; gradually expanding towards the apex. Antennal insertions visible from above, or hidden from above; not in fossae.
Cervical sclerites present. Pronotal length/maximum pronotal width 0.38–0.65. The pronotum with lateral keels (pronotal carinae); keels complete. Prothorax without notopleural sutures. Scutellum conspicuous to absent; when present, elevated above the mesoscutum in lateral view; anteriorly simple; posteriorly narrowly rounded or acute. The prosternal process complete; moderately or strongly overlapping the mesoventrite. Metaventrite with a transverse groove, or without a transverse groove. The fore-leg coxae countersunk in procoxal cavities. The fore-leg coxal cavities open behind externally; broadly open; quite widely separated; strongly transverse; without lateral extensions; internally open. 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; open laterally. Hind-leg coxae contiguous or narrowly separated, or widely separated; extending laterally to meet the elytra; posteriorly shaped to receive the retracted femur (with a sharp-edged declivity or hollow). Tarsal segmentation formula 5, 5, 5, or 4, 4, 4. The tarsi without bilobed segments; with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth, or without hidden segments (third segment lobed beneath, fourth small, fifth long, the terminal segment not as long as the other four together). 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, or distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple; with an empodium between them (this with no more than two setae). Hind tarsi with as many segments as the mid-tarsi; 4-segmented, or 5-segmented.
Elytral length/maximum width across the elytra 0.9–1.43. Elytra 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, or with six or more impressed striae; the lines per elytron 10, or 11. Scutellary striole absent. Elytra with epipleura to without epipleura. Elytral epipleura if present, falling short of the elytral tips (abruptly narrowed or excavated). Wings well developed, or absent or much reduced. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 5; comprising both fused and moveable components. Basal abdominal sternites immovably joined 2, or 3. Abdominal segment 8 apparently without functional spiracles. The male external genitalia trilobate.
Adult habitat, ecology. Land-dwellers.
Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized. The larvae elongate and more or less parallel-sided to oblong to ovate; C-shaped in lateral view to not C-shaped. Body circular in cross-section to somewhat 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 distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth, or multilobed or multidentate. The maxillary palps 4 segmented. The labium without ligula between the palps, or 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 or bilabiate); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.
Larvae not predacious; found under stones, in moss, in grass roots, etc.; phytophagous (feeding on bryophytes and lichens, also roots of angiosperms including grasses).
Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Byrrhoidea.
Representation in Britain and Ireland, and worldwide. About 280 species worldwide. 12 species in Britain; genera in Britain 6; Byrrhys, Cytilus, Morychus, Porcinolus, Simplocaria, Syncalypta. E.g., Byrrhus pilula ssp. dennii (Denny's Byrrhus); Simplocaria semistriata (Half-channelled Byrrhus).
General comments. Retracting the appendages tightly when alarmed.
Illustrations. • Byrrhus pilula ssp. dennii (Denny's Byrrhus: B. Ent. 135). • Byrrhus pilula ssp. dennii (details, B. Ent. 135). • Byrrhus pilula: B. Ent. 135, legend+text. • Byrrhus pilula: B. Ent. 135, text cont.. • Simplocaria semistriata (Half-channelled Byrrhus: B. Ent. 335). • Simplocaria semistriata (detail, dissections: B. Ent. 335). • Simplocaria semistriata (legend+text: B. Ent. 335). • Simplocaria semistriata (text, cont.: B. Ent. 335). • Byrrhus, Cytilus, Morychus, Syncalypta and Simplocaria (with Dermestidae etc.): Fowler 3, 97 (1889). • Fowler 3, 97 (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’.