Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


General appearance. 2.5–11 mm long. Body length/maximum body width 2.1–2.25. Beetles not necked; conspicuously waisted; neither particularly long- nor short-legged. Upper surfaces of body not bristly; with neither scales nor scale-like setae.

Detailed morphology. Inclination of the head strong to very strong. Eyes strongly protuberant; without bristles; finely facetted. Ocelli absent. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola; with well developed prosthecae, or with reduced prosthecae. 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, or somewhat expanded and truncate to subtriangular, or securiform to cultriform. The apical segment of the labial palps more or less expanded apically, or not expanded apically. Antennae short to long, but not exceeding the insect’s head to tail length; not elbowed; 11 segmented; pubescent or with modifications?; serrate, or pectinate (or with articulated appendages?).

Cervical sclerites present. The pronotum with lateral keels (pronotal carinae); keels incomplete. Posterior edge of the pronotum distinctly crenulate. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen; with neither produced front corners nor serrated sides. Scutellum conspicuous; elevated above the mesoscutum in lateral view; anteriorly notched; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate. The prosternal process complete; slightly overlapping the mesoventrite. The fore-leg coxae countersunk in ‘procoxal cavities’. The fore-leg coxal cavities open behind externally; broadly open; narrowly separated; slightly transverse; without lateral extensions; internally open. 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; open laterally. Hind-leg coxae contiguous or narrowly separated; extending laterally to meet the elytra. Tarsal segmentation formula 4, 4, 4. The tarsi with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth. Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented (with a reduced penultimate one); pseudotetramerous; the penultimate segment distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi one-toothed or bifid. Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytra exposing no more than part of the terminal tergite; striate (10 rows). Elytra with six or more longitudinal lines of punctures, 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, 10. Scutellary striole absent. Elytra with epipleura. Elytral epipleura reaching to the tips of the elytra. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 5; comprising both fused and moveable components. Basal abdominal sternites immovably joined 3. Abdominal segment 8 apparently without functional spiracles. The male external genitalia trilobate.

Adult habitat, ecology. On living vegetation (often found on foliage); mycetophagous (feeding on micro-fungi, using the modified maxillae to accumulate spores).

Larvae. Mature larvae minute (less than 3 mm long), or small to medium-sized (?). The larvae elongate and more or less parallel-sided. Body circular in cross-section. Vestiture restricted to fine hairs or setae. The larvae dorsally heavily pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented; 0.15–0.5 x the head width. Stemmata present; on either side of the larval head 1, or 6. The frontoclypeal suture between frons and clypeus distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles trilobed or tridentate. 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 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; in decaying plant material and in rotting wood (found in most conditions, but not adapted for surviving submerged); consuming decaying plant material, consuming rotting wood, and mycetophagous (?).

Classification. Suborder Polyphaga; Infraorder Elateriformia.

Representation in Britain and Ireland, and worldwide. 1 species in Britain (P. exotica); genera in Britain 1; Ptilodactyla.

General comments. The adults have brush-like maxillae, seemingly much modified for manipulating fungal spores.

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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.’.