Panagaeus Latreille, 1802
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ADEPHAGA Clairville, 1806
PANAGAEINI Bonelli, 1810
P. bipustulatus (Fabricius, 1775)
P. cruxmajor (Linnaeus, 1758)
Panagaeus are elongate, rather flattened and very distinctive ground beetles that should not be confused with any others, our UK species, which are also the only members of the genus to occur in Europe, are entirely black but for the elytra which have red with the base, suture and a broad median band black, hence the common name. Very rarely the transverse elytral band is diffuse or even interrupted at the suture and so the basal and sub-apical red marks are narrowly joined. The following description applies to both. 6.5-8.8 mm. Head elongate with large protruding eyes and short temples that converge strongly to a narrow neck, surface finely punctured and with scattered long setae, each eye with two long setiferous punctures along the inner margin although these can sometimes be difficult to see among the other setae. Maxillary palps very long, the terminal segment weakly securiform and attached eccentrically to the penultimate segment, labial palps much shorter with a broadly expanded apical segment. Antennae long and filiform, the basal segment longer and broader than the others, pubescent from the third segment. Pronotum broadest transverse to almost quadrate, broadest about the middle and narrowed to rounded basal and apical angles, surface densely and strongly punctured and with fine erect pubescence. Elytra elongate, with rounded shoulders and dilated to a continuously-rounded apical margin, striae moderately to strongly punctured and complete to the apex, interstices flat to moderately convex, pubescent and finely and roughly punctured. Legs long and slender, all tibiae with distinct apical spurs, front tibiae with a deep antennal-cleaning notch, all tarsi with five simple segments. Claws smooth and without a basal tooth. Basal segments of front tarsi dilated in the male.
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Our UK species may be separated as follows:
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-Smaller, 6.5-7.5 mm. Pronotum only slightly wider than long and not sinuate before the posterior angle, surface with a mixture of large and small punctures. Elytral interstices convex, apical red mark not reaching the lateral margin.
P. bipustulatus
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-Larger, 7.4-8.8 mm. Pronotum much wider than long and distinctly sinuate before the posterior angle, surface with fine punctures between larger punctures. Elytral interstices flat, apical red mark usually reaching the lateral margin.
P. cruxmajor
Panagaeus bipustulatus (Fabricius, 1775)
Widely distributed throughout Europe and extending into Asia Minor, Iran and western Russia, this species is locally common in some southern and central regions and rare in others e.g. it is red-listed in Switzerland where it occurs only on sunny hillsides between from about 350 to 1100 m, but very local and sporadic in the north, extending to the south-eastern coast of Sweden and the UK; it is local and rare across northern Germany and very rare and mainly coastal in Belgium, Denmark and the Netherlands, and there has been a general decline in many countries over recent decades. In the UK it is widespread across southern England and below the Wash and it occurs along the south coast of Wales, it is very local and generally scarce but adults can be common where they occur. The species occurs mostly in open dry habitats on chalky or sandy soils with short vegetation, often on chalk grassland hillsides exposed to the sun or on coastal dunes, but in the UK they also regularly occur among debris in marginal wetland situations, and on the continent they are sometimes very common in damp deciduous woodland. Adults are mainly diurnal and most active in the mornings when they may be seen running in bright sun on pathways through short vegetation, they are known to fly, having been recorded from light traps in Hungary, but they rarely do so and while UK specimens are fully-winged, some of those from the continent have reduced wings and poorly-developed flight muscles. The biology is poorly understood but adults occur year round, they are active over a long season from March until October and sometimes during mild winter spells, reproduction occurs in the spring and larvae develop through the summer to produce new-generation adults in the autumn.
Panagaeus cruxmajor (Linnaeus, 1758)
Crucifix Ground Beetle
Reputed to be among the rarest of our UK carabids, this species was formerly widespread across southeast England north to Yorkshire and regularly recorded but since 1980 it has appeared at a very few sites in Lincolnshire, Nottinghamshire, South Yorkshire and Carmarthenshire; the Nottinghamshire report is interesting as it is based on multiple observations from various sites along the river Trent, all of which seem to be new for the species and which might suggest a recent revival. A former UK stronghold was Wicken Fen in Cambridgeshire, made famous by Charles Darwin who, in an effort to secure a specimen, placed a bombardier beetle he was holding into his mouth in order to free his hands, with predictable results. It has long been known from various sites in the west of Ireland and these populations seem to be stable as there are modern records throughout the area. Further afield the species occurs throughout Europe except for the far north, although it seems to be very local and rare in many countries and has declined in the north over recent decades, across North Africa and on many of the Mediterranean islands, Asia Minor and through Russia to Mongolia and Siberia. Adults occur year-round and are active from March until June and again in the autumn, they overwinter under bark or among litter at the base of trees etc., and otherwise spend much of their time among vegetation and moss in marginal wetland situations. In central and northern Europe they occur on floodplains and permanently wet meadows and are sometimes recorded from well-vegetated coastal dunes, while in warmer southern areas they are sometimes abundant in damp deciduous forests. Most UK records are from wetland habitats and specimens have been netted from submerged marginal vegetation, and found dry salt marsh habitats. They are known to fly, although they are mostly nocturnal and this is rarely observed but a specimen was recorded alighting on an umbel flower. Little is known of the biology but both adults and larvae are very likely to be predaceous and it has been suggested that adults may be specialized snail feeders as they have a long forehead and palps like Cychrus, but this is only speculation, and, at least in Italy, the species is a spring breeder with larvae developing through the summer to produce adults in late summer and autumn. Adults can be found by general searching and turning over logs and stones etc. in damp marginal placed or by pitfall trapping although the latter tends to be destructive in such situations and should be employed with care.