Calodromius spilotus (Illiger, 1798)
Widely referred to in older literature as Dromius quadrinotatus (Zenker in Panzer, 1799), this species is generally common throughout Europe north to the UK and some central provinces of Fennoscandia, it occurs in north west Africa, through Asia Minor and western Russia and has been recorded from the eastern Palaearctic region, in the UK it is generally common throughout England and Wales, including all the islands, and rather more local and scattered further north to the Scottish Highlands and in Ireland. Typical habitats are open deciduous and mixed woodland, wooded parkland and often found on individual trees in hedgerows, verges and gardens, this species flies well and in spring and autumn should be expected on trees in most situations, it is exclusively arboreal and sometimes quoted as associated conifers, mostly pine and less often other species, and while this is true it will just as frequently be found on a range of deciduous trees e.g. in our local park they are frequent on Sycamore (Acer pseudoplatanus L.), Beech (Fagus sylvatica L.), Ash (Fraxinus excelsior L.) and London plane (Platanus x acerifolia (Aiton)), and we have found them on False acacia (Robinia pseudoacacia L.) in a local domestic garden. Adults occur throughout the year, peaking in abundance during the summer, they are nocturnal and active year-round in all but the very coldest spells and will sometimes occur in numbers on individual trees. Mating begins in late autumn and pairs will often be found on trees through the winter and into the spring, eggs are laid among bark in the spring and the predatory larvae develop through the spring and early summer. New generation adults occur from early summer, they are predatory and hunt other insects etc. among bark on trunks and low branches and may disperse by flight at this time. Adults are easily found by searching trunks at night, the majority of our records are from trees with smooth bark such as ash or beech because these are easy to search but they are frequent on most trees, just more difficult to find among deep bark such as oak. Searching through the winter at night can be very productive as mating pairs are common and they often occur alongside other species, especially various Dromius, and they may be active even when there is snow on the ground, searching by day is generally unproductive as they hide within crevices or under layers or bark rather than under loose bark and so are difficult to find. They sometimes occur in flight-interception traps and may be sampled with sticky things but so far we have not found them in light traps.
Calodromius spilotus 1
Calodromius spilotus 2
3.8-4.5 mm. Distinctive due to the flat body, dilated elytra and colour, head black, pronotum reddish-brown, elytra dark brown with two pale markings on each; a long subhumeral marking that generally does not reach the suture, and an apical mark beside the suture that usually does not reach the lateral margin, appendages pale brown. Head with large convex eyes and long converging temples, surface glabrous with fine granular microsculpture and two setiferous punctures beside each eye. Terminal maxillary palpomere cylindrical and finely truncate, antennae densely pubescent from the fourth segment. Pronotum quadrate, broadest behind rounded anterior angles and narrowed to projecting posterior angles, surface with transverse microsculpture radiating from a median longitudinal depression and elongate basal fovea. Elytra dilated from rounded shoulders to truncate and slightly sinuate apical margins, with a complete basal margin reaching the scutellum, finely impressed and punctured striae and microscopically granulate interstices. Distinguished from other maculate species by the small size, protruding posterior pronotal angles and dilated elytra which have a complete basal border.