Bitoma crenata (Fabricius, 1775)

With the possible exception of Cornwall Bitoma is widely distributed throughout England and Wales, including the Isle of Wight, below a line from Hartlepool to north Wales and there is also a solitary modern record from the Carlisle area (NBN). Fowler mentions a southern Scottish record which he goes on to say is 'almost certainly erroneous'. Typical habitat is beneath the bark of dead or decaying trees, fallen boughs and logs etc, more especially near the boundary of living and dead bark or where there is still sap. Beneath the bark of Quercus (Oak) and Fagus (Beech) may be favoured habitats (Alexander) but they also occur on a wide range of broadleaved species eg Aesculus (Horse chestnut), Betula (Birch), Acer (Sycamore) etc and probably also on conifers; Fowler quotes Fir and Pine. Adults occur year round and are often found in numbers; during the winter this is usually the case, they generally lie together in groups of a dozen or more and a single standing or fallen trunk may host several such groups. During the summer and autumn they have the unusual habit, for Colydiidae, of running on the warm surface of wood in bright sunshine, especially where the wood is devoid of bark or smooth, when disturbed they scatter and vanish into the nearest cracks and remain hidden for a few minutes. The species is common throughout our Watford area in woodland and parkland where there are older trees in various stages of decay. Any potential host is worth searching for the species eg at Radlett road we have found adults repeatedly under the bark of Salix (willow) logs despite never finding them under areas of damaged bark on nearby standing trees.
Both adults and larvae are carniverous feeding on other subcortical organisms, according to Fowler the larvae feed on the larvae of Tomicus species. Fully grown larvae are around 6mm in length; parallel sided and depressed and white with a reddish tinge on some parts of the body.
Although small Bitoma is of a very distinctive flattened, elongate shape and colouration and will soon be recognised even without a lens in the field. Teneral specimens (in our experience found late in the season) may have the elytra entirely orange or light brown but the overall form will be obvious, in any case they generally occur among other, mature specimens.

2.6-3.5mm Head and thorax black, elytra black, each with two discreet red or orange macula; one in the basal half and one subapically, these may be enlarged so as to almost unite at the middle. Head with dense flat tubercles from base to front of eyes, front of clypeus microsculptured and sparsely punctate. Antennae brown, 11 segmented with a 2 segmented club (segment 9 forming a transverse 'cupule'), inserted on side margin of head beneath a wide canthus in front of large, weakly convex eyes. Pronotum densely and rugosely punctured and with very fine recumbent pale pubescence. Transverse, side margins rugose and evenly curved to obtuse front and hind angles. Front angles protruding, front and hind margins sinuate. Disc with impressions, either side with two longitudinal raised ridges. Scutellum small and densely punctured. Lateral margins of elytra bordered and gently sinuate, humerus rounded and produced forward. Alternate interstices raised into narrow longitudinal ridges on which are pale semi-erect fine setae, between these ridges the striae are represented by two rows of shiny punctures. Legs red with femora and tibiae darker (when mature). Tarsi 4-4-4, claw segment longer than the rest combined. Claws prominent, weakly curved and without appendages.

From 4 Watford specimens at X40






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