EUCNEMIDAE | uk beetles

EUCNEMIDAE Eschscholtz, 1829

False Click Beetles

Includes mostly rare and local species, although Melasis is likely to be found in undisturbed woodland. All species are associated with decaying timber.

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POLYPHAGA Emery, 1886

ELATEROIDEA Leach, 1815

3-11mm

Introduction

This is a large and cosmopolitan family of about 1700 described species with many more awaiting description and it is thought that the true number will exceed 3000. On the other hand it is likely there will be changes; a recent system transfers the Thylacosterinae (with about 45 Asian and Australian species) and the Subprotelaterinae (with a single genus of 4 or 5 Oriental species) to the Elateridae. The greatest diversity occurs in tropical and subtropical regions with the Indomalayan zone being particularly rich; they are relatively poorly represented at higher latitudes e.g. 90 species have been recorded from the Nearctic and 90 from Australia with about the same number awaiting description, 30 or so occur in Europe and only 7 species occur in the U.K. Many species are listed as very rare or endangered in developed regions.

Ecology

They are small to medium sized beetles, elongate and variously flattened and pubescent dorsally, and the majority superficially and closely resemble elaterids, hence the common name, and many species are able to ‘click’ though in general not as powerfully as the true click beetles. Exceptions are species of Anischia Fleutiaux, 1896 and some Melasini. Some species may be abundant regionally, especially so in the tropics, but they are not obvious in the field and many are only poorly represented in collections. In general little is known of Eucnemid biology; most species, certainly in temperate regions, are saproxylic, occurring in lowland and mid-elevation wooded environments. Adults are associated with all types of wood from moist and decaying xylem to seasoned hardwood, and may occur in the soil around the roots of decaying or dying trees. Fungus is almost always present where the beetles occur, and a good way of sampling them is by beating or sweeping foliage or setting malaise or flight interception traps in suitable looking areas, many species also come to light. In temperate regions the adults often appear early in the year and have a long season even though they are usually short-lived; April to July is the best time to look for them but they are likely to be active from March to October. They sometimes emerge together in large numbers and swarm both by day and

in the evening over wood stacks etc. or around decaying trees. The larvae occur in a variety of habitats associated with trees e.g. among decaying wood in stumps, branches or logs etc. where they are thought to feed upon slime mould and mycelia etc. Broadly speaking the larvae form two groups; the Perothopinae and Phyllocerinae have soil or litter inhabiting larvae while members of the other subfamilies are saproxylic. Most temperate species overwinter in the larval stage and complete their growth and pupate the following spring or early summer, the entire life-cycle taking one or two, exceptionally three, years to complete. Pupation occurs in a cell near the surface of trunks or logs etc. and this stage is usually brief although the duration and timing of development may be prolonged or delayed in unfavourable conditions.

Larvae

The larvae of some species are hypermetamorphic with a free-living but non-parasitic triungulin first instar which will develop into a different form in later instars. Some species develop a pre-pupal stage after the fifth instar and before the proper pupal stage. They are distinguished from other elateriform larvae by the head structure; small and prognathous and lacking an epicranial suture and with tiny, 2-segmented antennae. The mandibles are small and fused to the head capsule, outwardly curved and sometimes equipped with lateral teeth. The labium and maxilla are reduced and the frons, clypeus and labrum are absent. Legs absent. The larvae in most cases live within a few centimetres of the wood surface and they have evolved into three very distinct types:

Fusiform larvae are soft and pale in colour with broad body segments, resembling dipteran larvae. The head is soft and furnished with 4-6 forwardly projecting teeth but lacks mandibles, and there are small maxillary and labial palpi beside the buccal cavity. These primarily occur in the tropics.
Elateriform larvae are elongate and thin, heavily sclerotized and dark or brown in colour, they superficially resemble elaterid larvae and are sometimes referred to as ‘wireworms’. They are distinct due to the head structure; the mandibles are tiny and have laterally projecting teeth, and the head capsule has small, extra teeth laterally. The surface of the body segments has microtrial patches which look like suede under high magnification.
Buprestiform larvae are soft-bodied with the thoracic segments greatly enlarged, as in buprestid larvae. These also have tiny mandibles furnished with outwardly projecting teeth. Some species have microtrial patches and in some there are modified scleromes on the first thoracic segment. These larvae often cut or bore across the grain of the xylem and have been called ‘cross grain borers’.

Description

Small to medium sized beetles, 2-30mm. Mostly elongate and variously Fusiform, convex; often strongly so but at least to some extent, mostly drab but sometimes with yellow or red markings and some tropical species are brilliantly coloured and/or metallic. Pubescence sparse to moderately dense, short and recumbent or semi-recumbent and directed backwards as in many elaterids. The head is generally narrower than the pronotum; hypognathous with large and coarsely faceted eyes. Antennae 11-segmented, often filiform and also often sexually dimorphic being serrate to strongly pectinate in the male; first segment elongate, second segment small and places eccentric upon the first. Antennal insertions close together and rather distant from the eyes. Mandibles robust, sharp and acute at the apex. Apical segment of the labial and maxillary palpi weakly securiform. Pronotum generally transverse with the hind angles weakly to moderately produced and the lateral margins carinate. Prosternal Mentum broadly rounded and flanked by antennal grooves and coxal cavities which are open posteriorly. Scutellum small and usually triangular. Elytra entire and covering the abdomen, rounded apically and with variously impressed striae which may be simple or punctured. Epipleura broad at the base. Abdomen with 5 segments, all of which are connate. Legs slender and relatively long; femur variously fusiform, tibiae long and slender. Tarsi 5,5,5 with the fourth and sometimes the basal segments bilobed, terminal segment long and slender. Claws simple.

The adults of most species superficially, and sometimes very closely, resemble elaterids with the fusiform habitus, convex pronotum and hypognathous head which is partly or even completely hidden in dorsal view, long legs and antennae, and most species have deep grooves beneath the thorax for the reception of the antennae. They differ from elaterids in lacking a distinct and free labrum and having the anterior margin of the prosternum straight rather than lobed although in a few primitive Eucnemids it is lobed and approaches the form found in the elaterids. The easiest way to identify a species as a eucnemid is by the placing of the second antennal segment upon the first; in Eucnemids it is always offset whereas in elaterids it is placed centrally on the end of the basal segment. While most species resemble elaterids some look very much like buprestids and some resemble cantharids but the antennal morphology will serve to separate eucnemids in all cases. Members of the Melasini are probably the most diverse group morphologically.

Classification

Anischiinae Fleutiaux, 1936 includes a single genus of 7 tropical saproxylic species.
Eucneminae Eschscholtz, 1829 includes 10 tribes:
- Dendrocharini Fleutiaux, 1920 includes 4 genera and was formerly a tribe of the Gastraulacinae.
- Dyscharachthini Muona, 1993 includes the single genus Dyscharachthis Blackburn, 1900.
- Entomosatopini Muona, 1993 includes the single genus Entomosatopus Bonvouloir, 1871.
- Eucmenini Eschscholtz, 1829 formerly the subfamily Gastraulacinae Fleutiaux, 1920. Includes 7 genera including Eucnemis Ahrens, 1812.
- Galbitini Muona, 1991 includes 4 genera.
- Mesogenini Muona, 1993 includes 12 genera.
- Perrotini Muona, 1993 includes the single genus Perrotius Fleutiaux, 1938.
- Phaenocerini Muona, 1993 includes 2 genera.
- Proutianini Muona, 1993 includes 3 genera.
- Muonajini Ozdikmen, 2008 includes the single species Muonaja yonde (Muona, 1993).
Macraulacinae Fleutiaux, 1923 includes 8 tribes:
- Anelastidini Muona, 1993 includes the single genus Anelastidius DuVal, 1863.
- Echthrogasterini includes 7 genera.
- Euryptychini Mamaev, 1976 includes the single genus Euryptychus LeConte, 1852.
- Jenibuntorini Mouna, 1993 includes the single genus Jenibuntor Muona, 1993.
- Macraulacini Fleutiaux, 1923 includes more than 80 genera.
- Nematodini Leiler, 1976 includes 5 genera.
- Oisocerini Muona, 1993 includes the single genus Oisocerus Bonvouloir, 1868.
- Orodotini Muona, 1993 includes 7 genera.
Melasinae includes 8 tribes:
- Calyptocerini Muona, 1993 includes 2 genera.
- Ceballosmelasini Muona, 1993 includes a single genus.
- Dirhagini Reitter, 1911 was formerly a subfamily, includes 24 genera.
- Epiphanini Muona, 1993 includes the genus Hylis Des Gozis, 1886 with 2 U.K. species.
- Hylocharini DuVal, 1859 includes a single genus.
- Melasini Fleming, 1821 includes 3 genera with Melasis Olivier represented in the U.K.
- Neocharini Muona, 1993 includes the single genus Neocharis Sharp, 1887.
- Xylobiini Reitter, 1911 includes 8 genera.
Palaeoxeninae Muona, 1993 Includes a single genus and the well-known ’ Dohrn’s Elegant Eucnemid Beetle’, Palaeoxenus dohrnii (Horn, 1878) a spectacular red and black species up to 20mm from coniferous forests in the western U.S.A and some Neotropical regions.
Perothopinae Lacordaire, 1857 includes 3 species of the genus Perothops, commonly known as Beech Tree Beetles.
Phlegoninae Muona, 1993 includes the very diverse Neotropical genus Phlegon (Laporte, 1840), resembling elaterids or dascillids, some males have exceptionally developed antennae.
Phyllocerinae Reitter, 1905 includes 2 tribes:
- Anelastini Reitter, 1921 includes the single Palaearctic and Nearctic genus Anelastes Kirby, 1818 with 5 species.
- Phyllocerini includes 3 genera, Holarctic, African and Madagascan.
Pseudomeninae Muona, 1993 includes 2 tribes each with a single genus:
- Pseudomenini Muona, 1993 includes the Australian Pseudomenes bakewelli (Bonvouloir, 1872).
- Schizophilini Muona, 1993 includes the Nearctic Schizophilus subrufus Randall, 1838, resembling a large red elaterid.