Nudobius lentus (Gravenhorst, 1802)
Included in our Watford list from specimens found in Whippendell wood during August 2009. Having identified the specimens we were surprised to find the distribution given by Joy as simply 'Scotland,4 (N.E.), under bark', looking to Fowler (from which Joy may have paraphrased his notes) we find the same distribution; 'under bark of scotch fir; very rare; Scotland, Dee and Moray districts.' The NBN (August, 2009) gives modern records from Aberdeen, Moray and highland but also gives a wide distribution in northeast Wales and the English midlands north to north Yorkshire with modern records from Anglesey, Cambridgeshire, Cheshire, Gloucestershire, Norfolk, Nottinghamshire and Wrekin, and two more southerly records from south Hampshire and West Sussex. Although there are no records from Herts it is thus perhaps not so surprising to find the species locally. Typical habitat is beneath the bark of conifers where both the adults and larvae feed on the larvae of various wood feeding beetles (Fowler). They have also, more recently, been found beneath the bark of hardwoods (Alexander). Our specimens were found under close fitting but loose bark on the top and sides of a fallen pine trunk, this was extensively excavated with galleries containing abundant adults and small (2-3mm) larvae of Drycoetes autographus (Ratz.) and Hylurgops palliatus and the occasional tiny Hylecoetus larva. Both scolytids had been present since April 2009, at which time the bark was healthy and difficult to remove, since then the subcortical space had progressively filled with damp black wood pulp and frass from the excavations, and it was among this we found the rove beetles; nineteen specimens were found under about half a square metre of bark, when uncovered they either remain stationary or move slowly towards the nearest debris.

Joy includes lentus, our only British species of Nudobius, within his key to Xantholinus, distinguished by the well developed terminal segment of the maxillary palps, the two longitudinal impressions on the head from between the eyes to the front margin, the longitudinal series of punctures either side of the pronotal midline and the overlapping elytra. Within his Xantholinus key the present species is distinguished by having 7-9 punctures in each pronotal series, bright red to yellow elytra and yellow legs(etc), a line drawing of the forebody is given.
Additional to this the form of the lateral margin of the pronotum is distinctive in Nudobius; here a very fine border is visible on the basal third (or so) of the lateral margin, from here forward it curves down and inwards so that it runs obliquely, on the ventral face of the reflexed margin, passing close to the outer margin of the procoxae and diagonally under the front and diagonally under the front angles towards the middle of the prosternal front margin.

6.5-7.5mm Appearance distinctive, entire upper surface of bosy with sparse long and pale pubesence. Head shiny black and slightly elongate; 9:8, length from back margin to the central projection on the anterior margin, width across eyes. Surface with large punctures; sparse on vertex and becoming dense laterally, and with very fine puncturation between these. Microsculpture transverse and sinuate. Eyes small and moderately convex, temples long and diverging slightly towards base, hind angles rounded to a curved hind margin which meets the neck at a right angle. Front margin of head with three forwardly projecting teeth, cuticle behind with two longitudinal depressions to between eyes. Mouthparts brown; last segment of maxillary palps as long as penultimate. Antennae pale brown or with terminal segment lighter, short and robust; basal segment as long as 2-5 combined, 4-10 strongly transverse. Pronotum black and shiny, as head, elongate (about 10:7), broadest at front angles and narrowed to hind angles, lateral margin sinuate behind middle. Front and hind angles rounded. Hind margin finely bordered - this is a continuation of the lateral border described above. With a longitudinal series of punctures either side of middle; generally 7-9 in number but one or several are occasionally missing or very weak, and with scattered large punctures towards the lateral margins, especially anteriorly, these may tend towards a longitudinal series. Entire surface with sparse and very fine puncturation. Scutellum shiny black, microsculptured as pronotum and with several large punctures. Elytra slightly elongate, about as long as pronotum, broadened towards apex. Testaceous, appearing yellow in sunlight, overlapping at suture, with a curved longitudinal ridge either side of suture between which the surface is impunctate. Surface shiny; microsculpture indistinct at X40, with large punctures mostly randomly arranged but tending to longitudinal series by suture and lateral margins. Hind margins separately curved. Abdomen shiny black or with terminal segment lighter, with sinuate transverse microsculpture (obscure at X40), side borders narrow and strongly raised, puncturation sparse and fine. Legs entirely pale. Front tibiae with a long, outwardly curved spine on inside at apex. Tarsi 5-5-5 with a very small basal segment so they may appear 4-4-4. Claws curved and smooth, with a weak tooth one third from base.

Description from 4 Watford specimens at X40