Perigona nigriceps (Dejean, 1831)
Perigonini Horn, 1881 is a cosmopolitan tribe of 5 genera and about 120 species, most of which are included in the genus Perigona Laporte, 1835. The tribe is often included within a broadly-defined Harpalinae Bonelli, 1810, the species are all small and flattened ground beetles characterized by the outer elytral stria which is strongly-impressed and continues around the apical margin. About 100 species are species are included in near-cosmopolitan genus Perigona which occurs almost worldwide but is most diverse in the Old World tropics. Members of the tribe are thermophilic, they occur among moss and bark on rainforest trees and among decaying organic matter in a wide variety of situations and some are associated with stored foodstuffs etc., they are predacious and many are nocturnal and come to light in large numbers. The very widespread P. nigriceps, which is native to tropical Asia and abundant around the Indian Ocean, has become almost cosmopolitan via the trade in crops and spices etc., it was first recorded in North America in the 1850s and is now established widespread, occurring in stored products and cellars as well as in the wild, it remains generally rare in Europe but there are widely scattered records north to the Baltic and it has known in the UK since the late 19th century. This is the only member of the genus recorded from the UK; it was first recorded here following a more general European expansion of its range and is now widespread though sporadic and very local across Wales and southern England and is very likely to be in the process of expanding its range here. Adults have been recorded over a long season from spring until autumn; they usually occur among warm compost and are occasionally attracted to light in numbers, on the continent they have also been recorded from moss and fungi on trees and from haystacks and farm refuse, and more generally they are associated with a range of food products in artificial conditions. Little is known of the biology in temperate regions but reproduction depends more on temperature and conditions rather than time of year and in its native sub-tropical regions (and probably also under artificially heated conditions elsewhere) it is continuously brooded. Adults are macropterous; they disperse by flight and have been recorded at light throughout their northern temperate range.
2-2.5mm Head black or dark brown with the labrum contrastingly paler, body otherwise pale brown or with the elytral margins variously darker, appendages entirely pale brown. Head smoothly convex, with large convex eyes and short, strongly converging temples, inner margin of eyes with 2 setiferous punctures, mandibles sharp and produced forward, not toothed and without setiferous puncture on outer margin, apical maxillary palpomere as large as penultimate, and antennae pubescent from the third segment. Pronotum strongly transverse, broadest in front of the middle and with rounded angles, lateral margins evenly curved, weakly explanate and bearing 2 setiferous punctures, the surface very finely punctured but without distinct basal fovea. Elytra broadly oval, with rounded shoulders and only slightly sinuate before a continuously-rounded apical margin, striae represented by rows of fine punctures; the eighth deepened from behind the shoulders, lateral margins finely pubescent throughout and the third interstice with 3 or 4 setiferous punctures. Front tibia with strong sub apical notch, all tibiae with a single apical spur. Fully winged, these usually being visible through the elytra. Male front tarsi not dilated but with rows of adhesive setae below.
The small size and drab colour is suggestive of various Trechinae but Perigona may be distinguished by the lack of furrows on the head, fully-developed maxillary palps and strongly-impressed eighth elytral stria.