Insects of Britain and Ireland: the families of Coleoptera
~ Hylophilidae, Xylophilidae.
General appearance. 1.5–2 mm long. Body length/maximum body width 1.4–3.1. Elytral length/pronotal length 2.7–5.2. 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-oval; conspicuously necked; somewhat waisted to conspicuously waisted; entirely reddish, or with head and thorax black. Upper surfaces of body glabrous or subglabrous, or non-glabrous; not bristly; with neither scales nor scale-like setae.
Detailed morphology. Beetles not prognathous. Inclination of the head strong. Eyes strongly protuberant, or not strongly protuberant; bristly, or without bristles; coarsely facetted (granulated). Ocelli absent. The labrum at least partly visible in antero-dorsal view; labrum mostly moderately to heavily sclerotized. Mandibles with a well developed mola. The mandibular apices 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. The apical segment of the maxillary palps somewhat expanded and truncate to subtriangular, or securiform to cultriform (being in male A. oculatus conspicuously expanded, spongy and pilose). The apical segment of the labial palps more or less expanded apically. Antennae about half the insect's head to tail length to long, but not exceeding the insects head to tail length, or longer than the insect's head to tail length (in male A. ocultus); 11 segmented; hairy. Antennal scape not swollen. Antennae filiform. Antennal insertions visible from above to hidden from above.
Cervical sclerites present. Prothorax about as long as wide. Pronotal length/maximum pronotal width 0.4–1.2. The pronotum without lateral keels. Prothorax at its widest markedly narrower than the adjoining part of the abdomen. Prothorax without notopleural sutures. Scutellum conspicuous; not elevated; anteriorly simple; posteriorly truncate to emarginate. The prosternal process complete, or incomplete; falling short of the mesoventrite. Metaventrite without a transverse groove. The fore-leg coxae countersunk in procoxal cavities. The fore-leg coxal cavities open behind externally; broadly open; medianly confluent, or narrowly separated; 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 narrowly separated; not or scarcely 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 4, 4, 4, or 4, 4, 3. The tarsi exhibiting bilobed segments (weakly), or without bilobed segments (lobed beneath only); those of the front and middle legs, and sometimes of the hind legs with a tiny penultimate segment hidden by distal lobing of the fourth and fused to the fifth (in all the legs the basal segment is very long, the antepenultimate one is lobed beneath, and the penultimate one is very small). Front tarsi with as many segments as the mid-tarsi; 5-segmented. Mid-leg tarsi 5-segmented; pseudotetramerous; the penultimate segment distinctly shorter than the antepenultimate one. The claws of the mid-leg tarsi not appendaged. The claws of the mid-leg tarsi simple (not split). Hind tarsi with one segment fewer than the mid-tarsi; 4-segmented.
Elytral length/maximum width across the elytra 1.15–2.52. Elytra covering most to all of the abdomen; exposing no more than part of the terminal tergite; without striae. Elytra apunctate, irregularly punctate, or each with fewer than 6 longitudinal lines of punctures or impressed striae. Scutellary striole absent. Wings well developed. Wings with an anal lobe. Wings with a medial fleck; the medial fleck not bisected by a vein. Abdominal sternites 4–5; comprising both fused and moveable components. Basal abdominal sternites immovably joined 2 (i.e., the two basal sternites immovable). Abdominal segment 8 apparently without functional spiracles. The male external genitalia tenebrionoid.
Adult habitat, ecology. Predacious, or not predacious (?); on living vegetation, or in rotting wood (usually found in or near old wood, or under leaves of trees and shrubs).
Larvae. Mature larvae minute (less than 3 mm long). The larvae elongate and more or less parallel-sided. Body somewhat flattened to strongly flattened. The larvae 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 2. The frontoclypeal suture between frons and clypeus indistinct or absent. The labrum and head capsule separated by a complete suture. Apices of the mandibles trilobed or tridentate. The maxillary palps 3 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 extending to the underside. The abdomen having functional spiracles on anterior segments; without spiracular tubes. The larvae without abdominal gills. The abdominal apex without a respiratory chamber. Abdominal tergum 8 without amature. The posterior segments without swimming hairs. The last abdominal segment with cerci.
Larvae probably not predacious; in decaying plant material; consuming decaying plant material (probably saprophagous).
Classification. Suborder Polyphaga; Infraorder Cucujiformia; Superfamily Tenebrionoidea.
Representation in Britain and Ireland, and worldwide. About 1000 species worldwide; genera about 50 (mostly tropical). 3 species in Britain; genera in Britain 3 (in recent lists); Aderus, Euglenes, Vanonus. E.g., Euglenes oculatus (Fly-headed Beetle).
General comments. Very small beetles resembling Anthicidae; head deflexed, sharply constricted behind the eyes; body pubescent, yellowish or brown. Tarsal segment numbers in published descriptions differ, presumably owing to occurence of tiny inconspicuous components.
Illustrations. • Euglenes oculatus (Fly-headed beetle): B. Ent. 299. • Euglenes oculatus: B. Ent. 299, (details). • Euglenes oculatus: B. Ent. 299, legend+text. • Eglenes oculatus: B. Ent. 299, text, cont.. • Euglenes oculatus and Aderus populneus (as Xylophilus), with Anthicus and Melo´dae: Fowler 5, 151 (1891). • Fowler 5, 151 (1891): 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’.