Trichonyx sulcicollis (Reichenbach, 1816)

Lasius brunneus
A very local and rare species; classed as RDB2 in Hyman and Parsons i.e. 'believed likely to move into the endangered category in the future if causal factors continue operating', 'species in vulnerable habitats...' and 'species declining throughout their range'. Prior to 1970 recorded from around 10 counties across southern England from Somerset to West Sussex, since 1969 from south Hants West Sussex and Surrey (Hyman and Parsons) and from south Buckinghamshire and Essex (Telfer and Hammond, 2007). Last recorded from Herts in 1940 (T.James, pers. comm.). Associated with rotten wood, especially Oak and Elm but also Beech, in ancient broad-leaved woodland and wooded pasture and recorded with the ants Lasius brunneus and L.niger. Adults have been found from May to August and during December and are probably predatory on mites (Hyman and Parsons). The Buckinghamshire record is interesting as the habitat described seems very similar to our single local record from Cassiobury park on 1st June 2008, a few minutes after taking a sample of moss and soil along with some dead wood from around an ant nest beneath a standing Beech stump, a single Trichonyx was seen to emerge from the disturbed soil and began to climb up the sunlit stump among numbers of the ant, Lasius brunneus ¹. The stump, about 5 metres high, dead and completely devoid of bark, has been a focus of interest as many Prionus elytra were found in the soil around the base during 2006 and 2007.

Our largest species of Pselaphinae, Trichonyx is easily identified by its broad form coupled with short maxillary palpi relative to the antennae; in all other 'broad' species the palps are at least as long as half the antennal length.

2.8-3.5mm. (Pearce), 2.4-3.8mm (Joy). Entirely testaceous. Head and pronotum with long, pale pubescence. Head narrower than pronotum (11:13), quadrate, vertex with deep horseshoe-shaped impression, temples evenly rounded to hind margin which is perpendicular to neck. Front margin of clypeus bordered. Mandibles produced forward. Antennae 11 segmented, inserted under raised part of head in front of eyes, basal segment elongate and broad, 2-9 quadrate, 10 larger and 11 forming a club. Last segment of maxillary palp elongate and pointed, penultimate small and quadrate. Pronotum pentagonal, broadest at rounded front angles and strongly narrowed to base, with a weakly impressed longitudinal furrow containing a large fovea towards base, from which forwardly oblique furrows connect each side to a strong lateral depression. Elytra and abdomen with fine, pale pubescence, elytra with several long and curved setae inside side borders and on surface, basal abdominal segments with several long setae. Elytra strongly bordered, evenly curved and widened from beneath a strong humeral prominence, hind margin weakly curved. With an entire, deeply impressed sutural stria and a much shorter stria from inside humeral prominence to before middle. First three (visible) abdominal segments with strongly raised side borders. Tarsi 3 segmented, basal segment very small, 2 and 3 elongate, about equal in length, each with a single claw.
In the male the femora and intermediate tibiae are slightly thickened (Pearce).

¹ Det. Dave Murray. Bolton,B. and Collingwood,C.A. 1975. Formicidae. RES Handbooks 3(c)

Description from 1 Watford specimen at X40

Telfer and Hammond, 2007. Saproxlic beetles of Langley park. The Coleopterist. 16(2) 53-70.