Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz


= Horiidae, including Tetraonychidae.

Oil Beetles, Blister-beetles.

General appearance. 7–32 mm long. Body length/maximum body width 1.1–7. Elytral length/pronotal length 0.4–5.4. 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 oval to elongate; abruptly conspicuously necked; somewhat waisted to conspicuously waisted (expanded at the distal part of the abdomen, rather than waisted); reddish yellow, or greenish-, violet- or bluish-black; exhibiting bright ‘warning colours’, or without ‘warning colouration’. 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, or not prognathous. Inclination of the head slight to very strong. Eyes strongly protuberant, or 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; with well developed prosthecae to without prosthecae. The mandibular apices simple, or 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, or with a single apical structure additional to the palp (some Nemognathinae); with stylet-like lobes, or without stylet-like lobes. The apical segment of the maxillary palps cylindrical to fusiform, or somewhat expanded and truncate to subtriangular. The apical segment of the labial palps more or less expanded apically, or not expanded apically. Antennae short to about half the insect's head to tail length; 6–11 segmented. Antennal scape not swollen. Antennae filiform. Antennal insertions visible from above; not in fossae.

Cervical sclerites present. Prothorax shorter than wide. Pronotal length/maximum pronotal width 0.47–1.6. The pronotum without lateral keels. Prothorax at its widest markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous to absent; when applicable not elevated; anteriorly simple; posteriorly narrowly rounded or acute, or broadly rounded or obtusely angulate, or truncate, or emarginate. The prosternal process present, or absent; when present, incomplete; when applicable, 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 applicable, open behind externally; broadly open; when present, medianly confluent; strongly transverse to slightly transverse, 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; not shaped posteriorly to receive the femur. Tarsal segmentation formula 5, 5, 4. 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 with an appendage, or not appendaged; appendages when present, not or only lightly sclerotized, or heavily sclerotized, blade-like, or heavily sclerotized, spine-like or bristle-like. The claws of the mid-leg tarsi simple, or one-toothed or bifid, or serrate, denticulate or pectinate (often with a sclerotized, blade-like process beneath each claw); with an empodium between them (this with no more than two setae), or without an associated empodium. Hind tarsi with one segment fewer than the mid-tarsi; 4-segmented.

Elytral length/maximum width across the elytra 0.35–3.3. Elytra individually distinctly tapered to their apices to not individually tapered; not meeting along the full length of the mid-line (their apices well separated); covering most to all of the abdomen, or short, exposing several terminal abdominal tergites (often); exposing no more than part of the terminal tergite to at least three complete abdominal tergites; not truncate; soft. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed, or absent or much reduced. 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 tenebrionoid.

Adult habitat, ecology. Not predacious; on living vegetation (in grassy places and on trees); mostly phytophagous.

Larvae. Mature larvae small to medium-sized to relatively large. The larvae elongate and more or less parallel-sided, or oblong to ovate; C-shaped in lateral view, or not C-shaped. Body circular in cross-section, or somewhat flattened. Vestiture restricted to fine hairs or setae. The larvae dorsally only very lightly pigmented or sclerotized; ventrally only very lightly pigmented. The antennae 1 segmented (coarctate forms), or 3 segmented (grubs). Stemmata present (grubs), or absent (coarctate forms); on either side of the larval head when present, 1. The frontoclypeal suture between frons and clypeus indistinct or absent (coarctate forms and some grubs), or distinct (some grubs). The labrum and head capsule separated by a complete suture. Apices of the mandibles with a single lobe or tooth. The maxillary palps 0 segmented (coarctate), or 3 segmented (grubs). The labium without ligula between the palps (coarctate), or without ligula between the palps to with a short ligula between the palps (grubs). Labial palps present and segmented (in grubs), or absent or non-segmented (in coarctate forms); in grubs, 2 segmented. Mesothoracic legs present and segmented (in grubs), or much reduced or absent (coarctate); of grubs, 3 segmented, or 5 segmented; with 1 moveable claw. Visible abdominal segments 9 (coarctate), or 10. Tergum 9 of the abdomen entirely dorsal. The abdomen having functional spiracles on anterior segments (annular); without spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment without cerci.

Larvae predacious; in bees' nests, eating the eggs, honey and pollen stores, but the family is also associated with egg caches of grasshoppers.

The larvae are heteromorpic (cf. Rhipophoridae), with the first instar triangulin, the second caraboid, the third and fourth scarabaeoid, the fifth coarctate (the over-wintering non-grub stage, which lacks functional mouthparts), and the sixth scolytoid.

Classification. Suborder Polyphaga; Infraorder Cucujiformia; Superfamily Tenebrionoidea.

Representation in Britain and Ireland, and worldwide. About 7500 species worldwide; genera about 120. 9 species in Britain; genera in Britain 3; Lytta, Meloë, Sitaris (Apalus). E.g., M. brevicollis (Short-necked Oil-beetle); A. muralis (Bees'-nest Beetle).

General comments. Moderate-sized beetles with rather soft integument, with some overseas species having maxillae are adapted for absorbing nectar. Secretors of the defensive blistering agent, cantharidin. In common with Cantharidae, Lymexylidae, Lampyridae, Lycidae, some Dermestidae, some Melyridae and some Staphylinidae, the undersides of some meloids lack the usual procoxal cavities.

Illustrations. • Lytta vesicatoria: B. Ent. 658. • Lytta vesicatoria: B. Ent. 658, legend+text. • Lytta vesicatoria: B. Ent. 658, text cont.. • Lytta vesicatoria (Janson 159). • MeloŽ brevicollis (Short-necked Oil-beetle): B. Ent. 279. • MeloŽ brevicollis: B. Ent. 279, legend+text. • MeloŽ brevicollis: B. Ent. 279, text cont.. • MeloŽ violacea (Oil-beetle: Giles Watson, photos). • MeloŽ violacea (Oil-beetle, female depositing eggs: Giles Watson, photos). • Apulus muralis (Beesí-nest beetle: B. Ent. 340). • Apulus muralis (details, B. Ent. 340). • Apulus muralis: B. Ent. 340, legend+text. • Apulus muralis: B. Ent. 340, text cont.. • Apalus muralis (as Sitaris), Lytta vesicatoria, MeloŽ 6 spp. (with Aderidae and Anthicus): Fowler 5, 151 (1891). • Fowler 5, 151 (1891): original legend.. • Apulus muralis, with unrelated taxa: Fowler Suppl. 19, 1913. • Fowler Suppl. 19, 1913: 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.’.