Scaphidema metallicum (Fabricius, 1792)

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POLYPHAGA Emery, 1886

TENEBRIONOIDEA Latreille, 1802

TENEBRIONIDAE Latreille, 1802

DIAPERINAE Latreille, 1802

SCAPHIDEMINI Reitter, 1922

Scaphidema Redtenbacher, 1849

Two subspecies, sometimes considered to be distinct species, are known from Europe; S. m. bicolor (Fabricius, 1798) is locally common but more or less restricted to Hungary, Slovakia, Ukraine and the Czech Republic, it is easily recognized by the red forebody contrasting with the metallic dark bronzy elytra. The nominate subspecies is common in suitable habitats (although in Romania they periodically occur in caves) throughout Europe from Spain to Western Russia and north to the UK and the far north of Fennoscandia, it has also been recorded from western Siberia and it is likely the distribution is continuous. In the UK it is widespread and locally common across central and south east England and generally scarce in the north, Wales and the west of England. Adults are present year-round; they are active over a long season from March or April and peak in abundance during May and June, they overwinter under bark of a range of deciduous trees or in moss and litter at the base of trunks and become active during mild spells, they are nocturnal and difficult to find, often appearing on small twigs or logs covered in rasupinate fungi or lichens. Typical habitats are open deciduous woodland and wooded parkland but they also occur on individual trees in lanes, hedgerows and gardens, they spend the day under loose bark or among fungi on extensively decayed trees and shrubs and become active at night, they usually occur as single specimens or pairs but numbers have been found in large fungi such as Cerioporus squamosus (Huds,) Quélet (1886) on which they are thought to feed. Larvae have been recorded through the spring and summer among decaying soft wood infested with moulds, often in older trees with extensive areas of dead wood, and they pupate in situ but otherwise little is known of the phenology of the species. The species is sometimes quoted as declining but may actually be under-recorded, they are not easy to find and may avoid detection altogether e.g., on the continent they have been recorded from Malaise traps set high in the canopy of deciduous trees. Sampling adults is best done by searching at night; they may be found under bark but this is generally destructive and so should be avoided, the best places are shady and moist areas with plenty of shrubs and hanging small branches and twigs that can be beaten or swept, they were previously frequent on elm but now probably most frequently occur on oak, beech, Hawthorn and sycamore, they will often be found in the vicinity of fungus but they frequently roam bark and denuded wood and so careful searching can be productive, they also occur among suitable extraction samples.

Scaphidema metallicum 1

Scaphidema metallicum 1

3.9-5.5 mm. Broadly oval, convex and more or less continuous in outline, dark reddish brown with the pronotal disc and elytra extensively metallic bronze and the lateral pronotal margins narrowly pale brown, glabrous except for the anterior clypeal margin and labrum with sparse pale pubescence, legs reddish brown and antennae dark brown with the base variably pale. Head small and broad with long converging temples and wide reniform eyes, surface finely and sparsely punctured, laterally expanded over the antennal insertions. Terminal maxillary palpomere cylindrical, antennae long and gradually thickened to a rounded terminal segment. Pronotum transverse, broadest between sharp posterior angles and narrowed to a strongly emarginate apical margin, the anterior angles protruding, lateral margin explanate and basal margin sinuate, surface uneven and finely punctured but without structure. Scutellum transverse, triangular and rounded. Elytra smoothly curved and narrowed from rounded shoulders to a continuous apical margin, each eight rows of larger punctures and wide interstices with one or two rows of much finer punctures. Legs long and slender with simple femora and finely pubescent tibiae which are hardly expanded towards the apex. Tarsi 5-5-4 with all segments simple, claws smooth and finely toothed at the base.