Insects of Britain and Ireland: the families of Coleoptera

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L. Watson and M. J. Dallwitz

Drilidae

False Firefly Beetles.

General appearance. 5–7 mm long. Body length/maximum body width 2.05–4.85. Elytral length/pronotal length 4.25–4.95. 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. Body (of males) not noticeably widest either behind the thorax, or at the rear. Beetles elongate; not necked; conspicuously waisted; with male elytra orange-brown, covered in pale hairs. Upper surfaces of body non-glabrous; not bristly; with neither scales nor scale-like setae.

Detailed morphology. The head not covered by the thorax. Inclination of the head slight to very strong. 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 (in males), or mostly membranous or only very lightly sclerotized (in females). Mandibles without a mola; without prosthecae. The mandibular apices simple. The incisor edges of the mandibles 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 very short (females), or about half the insect's head to tail length (males); (10–)11 segmented; filiform (moniliform, females), or pectinate (males). Antennal insertions visible from above; not in fossae.

Cervical sclerites present. Pronotal length/maximum pronotal width 0.47–0.68. The pronotum with lateral keels (pronotal carinae) (in males), or without lateral keels (in the anelytrous females); keels in the males, complete. Prothorax without notopleural sutures. Scutellum conspicuous (in the males,), or highly reduced (in females); in males, not elevated; anteriorly simple; posteriorly narrowly rounded or acute. The prosternal process present, or absent (in the anelytrous females); when present, complete, or incomplete; in males 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 (in the anelytrous females). The fore-leg coxal cavities in the males, open behind externally; broadly open; when present, medianly confluent, or narrowly separated; strongly transverse; without lateral extensions; internally open. The mid-leg coxae countersunk in ‘mesocoxal cavities’, or attached externally, in the absence of mesocoxal cavities (in the females); separated by in males, less than the shortest diameter of the cavity. The mid-leg coxal cavities in males, contiguous, or narrowly separated; not or scarcely oblique; open laterally. Hind-leg coxae contiguous or narrowly separated (males), or widely separated (females); extending laterally to meet the elytra (males), or not markedly extended laterally (females). Tarsal segmentation formula 5, 5, 5. The tarsi exhibiting 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 (anelytrous females), or distinctly shorter than the antepenultimate one (males). The claws of the mid-leg tarsi not appendaged (but with setae near their bases). The claws of the mid-leg tarsi simple; without an associated empodium. Hind tarsi with as many segments as the mid-tarsi; 5-segmented.

Elytra present (males), or absent (in the larviform females). Elytral length/maximum width across the elytra 1.7–2.16. Elytra (of males) covering most to all of the abdomen; exposing no more than part of the terminal tergite; somewhat truncate to not truncate; non-glabrous. Elytra when present, apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed (males), or absent or much reduced (females). Wings without an anal lobe. Wings without a medial fleck. Abdominal sternites 6–7 (males), or 9 (females); all articulated and moveable. Abdominal segment 8 with apparently functional spiracles. The male external genitalia trilobate.

Adult habitat, ecology. Predacious (on gastropods).

Larvae. Mature larvae small to medium-sized. The larvae elongate and more or less parallel-sided. Body 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 more or less heavily pigmented, or ventrally only very lightly pigmented. The antennae 3 segmented. Stemmata present; on either side of the larval head 1. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule completely fused, with no suture apparent. Apices of the mandibles with a single lobe or tooth. The maxillary palps 4 segmented. The labium without 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 extending to the underside. The abdomen having functional spiracles on anterior segments (biforous or bilabiate); with anterior and 8th-segmental spiracles borne at the ends of a series of spiracular tubes. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The last abdominal segment with cerci.

Larvae predacious (on slugs and snails).

Classification. Suborder Polyphaga; Infraorder Elateriformia; Superfamily Cantharoidea.

Representation in Britain and Ireland, and worldwide. About 80 species worldwide; genera 4. 1 species in Britain; genera in Britain 1; Drilus. E.g., Drilus flavescens.

General comments. The eyes are quite small, and circular, unlike those of Buprestidae. The adult female is more or less larviform, with adult legs and antennae but lacking elytra and wings.

Illustrations. • Drilus flavescens, male and female (with unrelated taxa): Fowler 4, 116 (1890). • Fowler 4, 116 (1890): original legend.. • Drilus flavescens (Rye & Fowler).


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’.

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