Trixagus dermestoides (Linnaeus, 1767)
POLYPHAGA Emery, 1886
ELATEROIDEA Leach, 1815
Trixagus Kugelann, 1794
This generally common species occurs from lowlands to about 1000 m throughout Europe from the Mediterranean north to central Fennoscandia and the UK and extending east through Russia and the Caucasus into Siberia, it is also present on many of the Mediterranean islands but absent from North Africa. In the UK it is locally common across England and Wales though more sporadic and scarce in the north and there are only a few records from Scotland. Adults occur year-round; they overwinter in grass tussocks or among bark etc. and are active over a long season from early spring until late in the autumn, they are both diurnal and nocturnal; by day they may be swept from vegetation, often in wooded areas or near trees in parkland etc. but they fly in warm weather, especially in the afternoon and evening, and often visit flowers where they are thought to feed on pollen or fungal spores, by night they will often be found on trunks and branches of (mostly) deciduous trees or swept from foliage. Breeding occurs in late spring and females oviposit in soil around the base of trees, especially birch (Betula L.) and beech (Fagus L.) but also others including pine (Pinus L.). Larvae develop through the summer feeding below the surface on mycorrhizal fungi associated with the roots, they are fully grown by August or September and now they move lower into the soil, generally to about 20 cm, where they will pupate in an earthen chamber. Adults eclose within three weeks but remain in situ until the following spring although specimens are sometimes recorded during mild winter spells. Most specimens die off during July and August but some persist into late summer and as they have been recorded into the autumn it is likely that at least some of the freshly-eclosed specimens emerge late in the year. Adults will soon appear by general searching and sweeping but they fly over long distances and often occur in gardens and other disturbed areas, in our experience they often frequent pub gardens and town centres and they sometimes come to light traps, especially in wooded areas.
Trixagus dermestoides 1
© Lech Borowiec
Trixagus dermestoides 2
2.1-3.2 mm. Elongate-oval and continuous in outline, body dark grey to brown and with fine pale pubescence, appendages brown, usually with paler tarsi. Head hypognathous and only narrowly visible from above, vertex evenly convex, frons with distinct and more-or-less parallel longitudinal keels , eyes weakly convex, elliptical and incised from the anterior margin to about half-way; with numerous facets between the apex of the incision and the posterior margin. Antennae inserted laterally beneath the anterior margin of the eyes, 11-segmented, basal segment broadly expanded to a truncate apex, second segment broad and slightly elongate, 3-8 short and transverse, and 9-11 form a long and asymmetric club. Pronotum transverse, broadest across the produced posterior angles and unevenly narrowed to a rounded (from above) anterior margin, surface evenly convex and without structure, and densely and moderately strongly punctured, these being confluent in places. Elytra broadest behind rounded shoulders and evenly narrowed to a continuously curved apical margin, with narrow striae complete to the apex and broad, flat and very finely punctured interstices. Legs long and flattened with femora only narrowly visible in normal setting. Tibiae parallel-sided, the front and middle tibiae curved, without apical spurs but expanded and with several short spines externally just before the apex. Tarsi 5-segmented; the basal segment long and thin and the penultimate segment deeply but narrowly lobed. Claws smooth and not toothed at the base. Males have long setae projecting around the apical margin of the elytra but these are usually only obvious in fresh specimens as they quickly become lost in life.
Superficially similar to other UK members of the family but distinguished by the ocular incision which extends to about half way across the eyes; in all other species they extend deeper, being separated from the posterior margin of the eyes by only two or three facets.