Gnathoncus nannetensis (Marsuel, 1862)

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HISTERIDAE Gyllenhal, 1808

SAPRININAE Blanchard, 1845

Gnathoncus Jacquelin du Val, 1857

This species occurs locally throughout most of the Palaearctic region from Europe to the far east of Russia and extends into South East Asia and Japan, it is widespread in North Africa and the Atlantic Islands, is present throughout Europe, extending beyond the Arctic Circle in Fennoscandia, and occurs on most of the Mediterranean islands. In the UK it is widespread across southern and central England north to the Humber and there are a few records from the Welsh Borders, there are a few older, or possibly misidentified, records further north into Scotland and Ireland, and while it is generally very local it is our most frequently recorded member of the genus. The typical habitat is woodland and wooded parkland and pasture etc where it is mostly arboreal, inhabiting avian nests but adults sometimes occur in fungi such as Dryad’s Saddle (Cerioporus squamosus (Huds.) Quélet (1866)) or Chicken-of–the–Woods (Laetiporus sulphureus (Bull.) Murrill (1920)), and are occasionally recorded from carrion.  Adults are present year-round, they are active from April until October and peak in abundance during June and July, possibly following emergence of the new-generation from recently vacated avian nests. Both adults and larvae predate other small invertebrates associated with nests etc., and larvae are thought to develop rapidly during spring and early summer. Adults are nocturnal and rarely seen in the open but may be sampled at any time from avian nests, they occur in vacated bird and bat nesting boxes, among wood debris in tree hollows, and may be attracted to carrion-baited traps placed in trees. More generally they occasionally occur in mammal nests and in carrion in any situation e.g., in rabbit or deer corpses or among decaying fish on water margins, and in Europe are very occasionally recorded from mammal droppings.

Gnathoncus nannetensis 1

Gnathoncus nannetensis 1

Gnathoncus nannetensis 2

Gnathoncus nannetensis 2

© U.Schmidt

2.5-4.0 mm. Broadly elongate and almost continuous in outline, body shiny black, appendages black or with the antennal clubs and tarsi brown. Head convex anteriorly but almost flat between large and slightly protruding eyes, surface finely and rather sparsely punctured throughout, frons not bordered inside the eyes and antennae inserted in a small scrobe by the base of the eyes. Basal antennomere expanded and strongly angled, second segment broad and globular, 3-7 short and transverse, and 8-11 form an almost circular club. Pronotum Broadest across the base and narrowed to rounded and slightly projecting anterior angles, basal margin produced towards the centre, surface smoothly convex and punctured throughout, without impressed lines before the margins and with punctures becoming denser and a little stronger towards the lateral margins. Prosternum not produced into an anterior lobe. Elytra with four striae that extend into the middle and a short (at most 0.3X the elytral length) sutural stria, surface punctured throughout; finely so across the base and becoming stronger from the middle towards the apex, surface smooth and shiny throughout; not rugose towards the apex. Pygidium with rather dense circular punctures throughout. Front and middle tibiae strongly broadened from the base and toothed along most of the external margins, hind tibiae less strongly broadened and with a few small teeth towards the apex. Tarsi with 5 simple segments.