Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


= Lymexylonidae; including Atractoceridae.

Timber-borers, Ship-timber beetles, Ambrosia beetles.

General appearance. 7–18 mm long. Body length/maximum body width 4.05–12.2. Elytral length/pronotal length 1.5–5.25. 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 to slender; conspicuously necked to not necked; somewhat waisted. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. Eyes 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 reduced mola, or without a mola; with well developed prosthecae, or without prosthecae. The mandibular apices simple. The incisor edges of the mandibles simple, or with a single tooth. The maxillae with distinct galea and lacinia apically to the palp. The maxillary palps unique in having the penultimate segment bearing a large, complexly multi-lobed sensory organ; apical segment of the maxillary palps cylindrical to fusiform. The apical segment of the labial palps not expanded apically. Antennae short; 11 segmented; without a much-elongated scape. Antennal scape not swollen. Antennae filiform (or fusiform), or serrate (in Hylecoetus). Antennal insertions visible from above, or hidden from above.

Cervical sclerites present. Prothorax longer than wide. Pronotal length/maximum pronotal width 0.75–1.5. The pronotum with lateral keels (pronotal carinae), or without lateral keels; keels when present, complete, or incomplete. Prothorax at its widest not markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; not elevated; anteriorly simple; posteriorly broadly rounded or obtusely angulate, or truncate. The prosternal process present, or absent; when present, incomplete; when present, falling short of the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in ‘procoxal cavities’, or attached externally, in the absence of procoxal cavities. The fore-leg coxal cavities when present, open behind externally; broadly open; when present, medianly confluent; strongly transverse to slightly transverse (if present, in Lymexylon,), or 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. The mid-leg coxal cavities contiguous; markedly oblique; open laterally. Hind-leg coxae contiguous or narrowly separated; extending laterally to meet the elytra (Lymexylon), or not markedly extended laterally (Hylecoetus). Tarsal segmentation formula 5, 5, 5. 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; with an empodium between them (this sometimes with three or more setae). Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytral length/maximum width across the elytra 1.45–4.67. Elytra individually distinctly tapered to their apices to not individually tapered; not meeting along the full length of the mid-line (at least, narrowly separated towards their tips); fairly short, exposing several terminal abdominal tergites (in the British representatives); exposing no more than part of the terminal tergite to at least three complete abdominal tergites (the abdominal tip pointed); truncate; soft; non-glabrous. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed. Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 5–7; all articulated and moveable. Abdominal segment 8 apparently without functional spiracles. The male external genitalia cucujiform.

Adult habitat, ecology. Boring into living wood (causing fungal infections on which the larvae feed), or boring into dead wood.

Larvae. Mature larvae small to medium-sized to relatively large. The larvae elongate and more or less parallel-sided. Body circular in cross-section. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata absent. The frontoclypeal suture between frons and clypeus indistinct or absent, or distinct. The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth. The maxillary palps 3 segmented. The labium with a short ligula between the palps, or with a ligula at least as long as 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 extending to the underside. The abdomen having functional spiracles on anterior segments (these annular or annular-multiforous); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae in tunnels bored in the wood of weakened trees; mycetophagous.

The larvae boring into living and decaying wood; elongate, thin, cylindrical with short but well developed legs, prognathous with 3-segmented antennae, the sclerotized pronotum partially hooding the head.

Classification. Suborder Polyphaga; Superfamily Lymexyloidea.

Representation in Britain and Ireland, and worldwide. About 40 species worldwide; genera 7. 2 species in Britain; genera in Britain 2; Hylecoetus, Lymexylon. E.g., H. dermestoides; L. navale (Windsor Wood-borer).

General comments. Elongate, soft bodied beetles. Worldwide variation ranges from forms with elytra so short that they do not reach the abdomen, to others in which they cover all except the terminal tergite. In common with Cantharidae, Meloidae, Lampyridae, Lycidae, some Dermestidae, some Melyridae and some Staphylinidae, the undersides of some lymexylids lack the usual procoxal cavities.

Illustrations. • Hylecoetus dermestoides: B. Ent. 654. • Hylecoetus dermestoides: B. Ent. 654, legend+text. • Hylecoetus dermestoides: B. Ent. 654, text cont.. • Hylecoetus dermestoides (Rye & Fowler IX6). • Hylecoetus dermestoides (Janson 162). • Lymexylon navale (Windsor Wood-borer: B. Ent. 382). • Lymexylon navale (details, B. Ent. 382). • Lymexylon navale: B. Ent. 382, legend+text. • Lymexylon navale: B. Ent. 382, text cont.. • Hylecoetus dermestoides and Lymexylon navale (with Ptinidae, Cleridae, etc.): Fowler 4, 116 (1890). • Fowler 4, 116 (1890): 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.’.