Calosoma inquisitor (Linnaeus, 1758)
This is a very widespread species occurring across the Palaearctic region from the west of Europe and North Africa through Asia Minor, western Asia and into Siberia and there are isolated populations further east to Japan, it extends north into the UK and, rarely and very sporadically, southern Fennoscandia. There are a few early 19th century records from Ireland but it is thought to be long extinct. In the UK it is very local and generally scarce throughout southern and western England and Wales, generally absent from eastern England and southern Scotland and rare further north to the Scottish Highlands. The species is associated with oak in open and old-established woodland where the adults predate various moth larvae in the canopy during the day, they also hunt on the ground and may be found in the evening low down on trunks, it is more oligotrophic than C. sycophanta and prey are generally restricted to various Tortricidae e.g. The green oak tortrix, Tortrix viridiana L., and Geometridae e.g. The winter moth, Operophtera brumata L. Adults occur year-round and are active from May until July, peaking in June to coincide with prey abundance, they remain under bark or in crevices at night and overwinter in deep underground cells, numbers may be low or the species may appear to be missing for several years but may suddenly become very common in parallel with an explosion of lepidopteran larvae. Mating occurs in the spring and females oviposit in the ground. The larvae are terrestrial predators, they develop quickly and pupate in the ground to produce adults in late summer or autumn which generally remain in situ until the following year.
Among our UK fauna C. inquisitor is very distinctive and only likely to be confused with the larger and more colourful C. sycophanta (L.) 16-22mm. Entirely dark metallic bronze, often with a greenish or reddish lustre, underside dark metallic greenish or brassy. Head transverse with very convex and prominent eyes, robust and prominent mandibles and long, thin antennae. Vertex and frons flat and roughly sculptured, palps long and slender, the terminal segment truncate and only weakly dilated. Pronotum widely transverse, strongly rounded and contracted to produced posterior angles, raised lateral margin not continued to the base, surface roughly punctured, depressed inside posterior angles and usually with a fine longitudinal median furrow. Elytra with broad shoulders and weakly broadened towards a strongly narrowed apical margin, each with 15 finely punctured striae complete to apex and a short scutellary striole, interstices weakly convex and with regular transverse impressions which produce a characteristic appearance; the fourth, eighth and twelfth with a series of 6 to 10 contrastingly coloured, usually bright red or coppery, setiferous punctures which may occasionally join an adjacent stria. Legs robust and notably long. Male pro-tarsi with segments 1-4 dilated.