Cychrus caraboides (Linnaeus, 1758)
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ADEPHAGA Clairville, 1806
CYCHRINI Perty, 1830
Cychrus Fabricius, 1794
A very widespread species and probably the most common member of the genus, it occurs throughout Europe and across Russia; from Spain to Iran and north including Sweden and Norway and across the Finnish and Russian Taiga forest. Four subspecies are known; laticollis Jeanne, 1972 and zariquieyi Born, 1924 from Spain, costae Emery, 1872 from Italy and the widespread rostratus Linnaeus, 1761 which occurs in the U.K. The U.K. distribution includes the mainland and the islands north to Orkney and Shetland. Adults occur year round in damp woodland and upland heather moors and are sometimes gregarious; they spend the winter under logs etc. and may be found at this time in small groups. Larvae occur during autumn and winter from autumn breeding. Adults may stridulate when handled. Both adults and larvae feed on snails, especially the small Oxychilis species. Within the U.K. fauna Cychrus could only be confused with species of Carabus but the deeply bilobed labrum and elongate head and mandibles are distinctive. It is the only UK representative of the tribe.
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14-19mm. Entire body and appendages black. Head very elongate with deeply excised labrum and long, sharp mandibles, each with two sharp teeth internally. Each side with a ridge from the inside margin of the eyes forward over the antennal insertions. Finely punctured and rugose behind the protruding eyes. Palps elongate with dilated apical segments; these are sexually dimorphic, being much more developed in the male. Antennae long and slender; pubescent from the fifth segment. Pronotum quadrate; convex on disc and deeply depressed before hind margin. Widest about middle and with lateral margins strongly bordered. Surface shiny; unevenly punctured and sculptured. Hind angles rounded and hind margin straight, not produced backward. Elytra convex and ovate, abruptly depressed towards scutellum and weakly produced at apex. Strongly bordered, explanate towards apex. Surface granulate and uneven, sometimes this sculpture is coalesced laterally forming one or two weak striae.
CYCHRINI Perty, 1830
On a world scale this is a large tribe containing two very distinctive and superficially different sub-tribes.
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The PAMBORINA Hope, 1838 contains two genera which occur in Australia and New Zealand. These species look more like Carabus species than the typical form of the Cychrini e.g.Cychrus.
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The CYCHRINA s.str. is a Holarctic sub-tribe with numerous species in four genera:
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Sphaeroderus Dejean, 1831 contains five North American species.
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Scylinotus Dejean, 1826 contains eight sub-genera and many species.
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Cychrus Fabricius, 1794 A Holarctic genus with around one hundred and ten species. About twenty five are Palaearctic and of these fifteen occur in Europe. Three species are found in North America. About fifty species inhabit the mountain forests of Europe and Asia.
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Scaphinotus DeJean, 1826 A nearctic group of fifty-five species in nine sub-genera. Most species are nocturnal snail predators occuring in grasslands and forested areas.
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Members of the Cychrina are very characteristic species which, because of their specialized feeding habits, are known as snail hunters.
CYCHRUS FABRICIUS, 1794
Without experience the species of this genus are reminiscent of Carabus but the short, convex elytra and elongate head and mouthparts soon become obvious. Most species are unmetallic black or brown but there are some spectacular exceptions e.g. Cychrus aeneus Fischer Von Waldheim, 1824 from the Caucasus. The elytra are usually oblong or oviform and very convex, the surface varies from smooth to longitudinally sculptured and they are generally fused. Wings absent. It is worth looking at some North American species as these have developed large tubercles on the elytra, but the overall form of the tribe is still obvious. (see BugGuide.net). The palps are generally very prominent, and sexually dimorphic, and the labrum is deeply incised. The larvae are broad and flattened with antennae longer than the width of the head but with the circus very short. Larval mandibles are sharp with the retinaculum toothed. Adults and larvae of all species are specialized snail hunters and many have been also been observed preying on slugs. With their prolonged head and slender pronotum they are able to get past the operculum and attack the snail inside the shell. Larvae penetrate snail shells with their ventral side towards the shell so as to avoid getting the stigma plugged with mucus.
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Five species of Cychrus occur in France and one, C. attenuatus Fabricius, 1792, is featured to show how the sculpture of the elytra varies within the group. C. attenuatus is another widespread species, probably the most widespread after caraboides; it occurs throughout Europe and east to the Ukraine but does not range so far north as caraboides. They occur in small numbers in old growth woodland, often on slopes in hilly areas. The species may be under recorded as they are active in milder months and difficult to find but during the winter they remain under logs and are obvious. In France several varieties have been named from various regions e.g. var intermedius Heer is an alpine form with a small, cordate pronotum and very convex elytra, it occurs in the Alps and around Mont Blanc. In the Italian Maritime Alps and Ligurian Apennines the species is represented by var. Liguricus Straneo.
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The species is generally dark with a bronze or brassy lustre to the elytra but completely black specimens occur. The longitudinal sculpture on the elytra is obvious. The following description of attenuatus is purely for interest and will not be useful in identifying a European specimen. Head smooth in front of eyes, finely punctured and cross-striate behind. Antennae slender and red from segment five or six. Pronotum quadrate and flat, evenly rounded and with strong lateral borders. Disc smooth, surface punctured and rugose towards margins. Depressed in front of hind margin. Hind angles obtuse and hind margin straight. Elytra dark or, commonly, with a bronze lustre. With strong, granular surface structure which, especially towards the suture, form longitudinal striae. Each with three rows of elongate, glabrous and shiny granules which form distinct and outstanding striae. Elytral margin narrowly explanate, becoming a little broader towards the rear, especially in the male. Mouthparts and tibiae pale. Terminal segment of palps much broader in the male.