Nargus wilkinii (Spence, 1813)

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

LEIODIDAE Fleming, 1821

CHOLEVINAE Kirby, 1837

CHOLEVINI Kirby, 1837

Nargus Thomson, C.G., 1867

This widespread European species is generally common from the Pyrenees into central regions but rare and sporadic in the east, extending as far as Poland and Latvia, it has only rarely been recorded from Spain and Portugal but there is some evidence that it may be expanding there, to the south it extends into Italy and the Balkans and to the north to the UK and some southern provinces of Fennoscandia where it is mostly coastal. In the UK it is locally common across England and Wales though less so in the West Country and the north, and there are scattered records from Scotland and Ireland. Adults are present throughout the year and are active in all but the coldest winter spells, they peak in abundance from March to May and again in September and October, and are much less common (or active) during July and August. Typical habitats are open woodland and mature wooded parkland where adults may be sieved from accumulated leaf-litter and other organic debris but they occasionally occur among detritus in tree hollows and among decaying fungi etc. They are also associated with avian nests and mammal burrows, mostly those of rabbit and badger, although this association is not so strong as with some other members of the tribe e.g. Catops tristis (Panzer, 1794). Little is known of the biology but we have recorded the species from an old Jay nest during the winter in South Herts. and so the overwintering sites may be varied and not necessarily associated with mammal burrows, and the phenology would suggest a spring breeder with new-generation adults appearing in late summer. Adults are sampled by sieving old leaf-litter and here they may occur in numbers, they are also likely to appear in suitable extraction samples at any time.

Nargus wilkinii 1

Nargus wilkinii 1

2.2-2.4 mm. Elongate-oval with the pronotum and elytra discontinuous in outline, body and appendages entirely pale to dark brown, dorsal surface finely and randomly punctured and with fine recumbent pubescence throughout. Similar to some species of Choleva Latreille, 1797 but smaller, broader and with shorter appendages. Head widely transverse and smoothly rounded from above, with small convex eyes before a sharp occipital crest, frontoclypeal suture clearly defined. Maxillary palps robust, the penultimate segment much broader than the fusiform terminal segment. Antennae gradually and only weakly expanded; the second segment at least as long as the third and the terminal segment shorter than 9 and 10 combined. Pronotum transverse, broadest towards the base and narrowed to a rounded apical margin, the anterior angles hardly visible from above, basal margin straight on very slightly sinuate and the surface distinctly shagreened between fine punctation. Elytra narrower across the base than the base of the pronotum and at the widest point, about the middle, almost as wide as the pronotum, smoothly curved in outline and continuously curved apically, with a variously-developed sutural stria but otherwise smooth, punctures fine and dense throughout; in places arranged in transverse series but without distinct transverse striae. Legs long and slender with tibiae gradually and only weakly expanded from the base, middle and hind tibiae with stout terminal spurs, front tibiae with four apical spurs but without a row of shorter spines. Tarsi 5-segmented; all segments simple in the female, basal segments of front tarsi strongly expanded in the male.

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