Carabus clatratus Linnaeus, 1761
This widespread Palaearctic species occurs throughout central and northern Europe and Asia from France and Ireland to Japan and Korea, extending north to the Arctic Circle in Scandinavia although it has been in decline over recent decades and in Europe generally is among the most vulnerable and threatened carabids, being already extinct in some areas e.g. England and Switzerland. Factors such as climate change, habitat succession and land drainage are thought to have contributed to the decline although in Italy, and possibly also France and other central regions, its disappearance may be due to the spread of the invasive red swamp crayfish, Procrambus clarkii (Girard, 1825), a native Nearctic species known to prey on adult Carabus. In the UK it is a very local and rare species of northwest Scotland, including the Western Isles, and Northern and Western Ireland. Along with C. granulatus, with which it often occurs, C. clatratus is among the most hygrophilous of all European Carabus; it is generally a lowland species, occasionally extending into mountain valleys, and typically occurs in wet forests, swamps and bogs, lake margins, floodplains and salt marshes, they often occur among dense but patchy vegetation that extends into the water but they are not found in Sphagnum bogs. Typical of the genus both adults and larvae are predatory, adults prey mostly upon earthworms and other insects among vegetation etc and they have been observed feeding on carrion, but they are also amphibious and enter the water to hunt aquatic insects and their larvae, crustaceans, molluscs, tadpoles and small fish etc, this is partly facilitated by their carrying a supply of air under the elytra. Adults occur year-round and are active from April until September or October, they are diurnal but spend much of their time under logs, in Salix stumps or among matted algae and while most specimens are macropterous a small number are fully-winged and capable of flight. In northern latitudes C. clatratus is a late spring and summer breeder, the female excavates shallow depressions in the ground where she deposits a single egg which she covers with soil etc., this continues over a period of about two months but fecundity is low and each female will lay around ten eggs. Larvae develop through the summer, they pass through three instars, the first two develop rapidly but the
third, and the stage where mortality is highest, lasts much longer; they are very active nocturnal terrestrial predators and often turn up in suitably placed pitfall traps. Pupation occurs under logs etc. or in the soil from late summer and new generation adults appear in the autumn; these may remain inactive or feed for a while before finding suitable overwintering sites, possibly away from the breeding sites. Adults are best sampled from pitfall traps placed among vegetation in marginal habitats but may be found active or under stones or logs during the day and they have been recorded from inside stacks of drying peat.
Adults are large, 22-30mm, with a distinctive elytral structure that should not be confused with any other UK species. Entirely black, including all the appendages, generally with a brassy or greenish reflection and contrasting, golden or coppery, elytral fovea. Head, including the robust and protruding mandibles, elongate, with convex and prominent eyes and finely punctured and rather flattened vertex. Pronotum transverse, rounded laterally and sinuate before weakly produced posterior angles, with a wide and deep central depression behind the middle and elongate and deep basal fovea. Elytra with three strongly raised ridges which continue almost to the apex, between these with about ten wide and deep fovea separated by a variously raised, often elongate, tubercle, lateral margins explanate and roughly sculptured. Legs long and slender, each tibia with two strong apical spurs, front tibiae without an internal antenna-cleaning notch, male pro-tarsal segments widely dilated.