Agathidium nigripenne (Fabricius, 1792)

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POLYPHAGA Emery, 1886

STAPHYLINOIDEA Latreille, 1802

LEIODIDAE Fleming, 1821

LEIODINAE Fleming, 1821

AGATHIDIINI Westwood, 1838

Agathidium Panzer, 1797

This is one of the more common and widespread of the Western Palaearctic members of the genus; it is locally common throughout Europe though absent from the Iberian Peninsula, most of the Balkans and some of the Baltic countries, although it does extend far beyond the Arctic Circle in Norway and Finland, to the east it occurs across Asia Minor and parts of north-west Russia and in general it appears to more common in northern parts of its range. In the UK it is locally common across England and Wales though largely absent from the West Country and less common in the north, there are a few scattered records from Northern Ireland and Scotland north to the Orkney Islands. Adults occur year-round; they overwinter among decaying wood in stumps and logs or under loose bark or litter and are active over a long season, peaking in abundance from April until June and again in late summer and early autumn. Habitats include damp deciduous woodland, wooded parkland and carr with a good supply of fallen and decaying timber although they may also appear under bark or in logs in marshes or beside moorland ponds, they are sometimes quoted as preferring Beech, but locally they occur mostly on Poplar  and Willow Adults are nocturnal and usually occur among logs or low down on damp trunks, usually in the vicinity of fungi, and they often occur in soft, fleshy sporocarps, they are mycophagous and are known to spread spores of Ganoderma applanatum (Pers.) Pat. when they disperse in the summer. Mating occurs in the spring and females are thought to oviposit among damp wood infested with slime moulds. Larvae develop in damp decaying wood and are known to feed on slime moulds (a common name sometimes used for members of the genus is ‘slime-mould beetles’), and they probably pupate among the wood during late summer as teneral adults have been observed in late summer and autumn. Adults may be found by searching under damp bark of a range of broadleaf trees, they have also been recorded from various conifers, though much less frequently, at light, flight-interception traps and on ivy blossom in the autumn. By far the easiest way to record them is by searching among damp logs at night; they roam on the surface and disperse over short distances in the spring and at this time they sometimes appear on fences or higher up on trunks, at a local site they sometimes appear in pairs on wooden refuse containers placed by pathways in front of large willow trees and logs along the River Colne banks. Mature specimens can be recognized by the bicoloured body.

Agathidium nigripenne 1

Agathidium nigripenne 1

Agathidium nigripenne 2

Agathidium nigripenne 2

Agathidium nigripenne 3

Agathidium nigripenne 3

Agathidium nigripenne 4

Agathidium nigripenne 4

2.0-4.0 mm. Tiny and globular; set, or extended, specimens display the separately-rounded pronotum and elytra and the head is often raised so that the long temples are visible, but in the wild they are contracted to form a near hemispherical form, and when disturbed they display thanatosis and roll into a tight ball so that the features are lost. Dorsal surface glabrous and shiny; forebody reddish-brown, elytra black, legs pale brown, antennae pale brown but extensively darkened apically. Head and pronotum sparsely and very finely punctured, elytra a little more strongly and densely punctured. Head transverse, evenly curved anteriorly from the posterior margins of the eyes, temples strongly contracted behind the eyes then parallel-sided to the pronotum; immediately behind the eye a short, oblique post-ocular ridge is visible from above, surface evenly convex throughout. Maxillary palps short, the terminal segment not expanded, antennae inserted on the anterior margin in front of the eyes; 11-segmented with a distinct 3-segmented club, segment three as long as 4-6 combined. Pronotum widely transverse and strongly curved laterally, surface evenly convex and without impressions or sculpture. Metasternum without femoral lines. All specimens examined have been fully-winged. Elytra slightly elongate, broadest towards the base and strongly curved laterally, in side view the humeral angle is obtuse and distinct, surface with finely and closely punctured striae and a distinct impressed sutural stria, at least in the apical half. Legs short and robust, the femora not visible from above, tibiae gradually widened from the base and narrow throughout, all with obvious apical spurs. Tarsi 5-5-4 in the male, 5-4-4 in the female, and without obviously lobed segments.

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