Bembidion Latreille, 1802
This is the most speciose genus within the Carabidae with more than 1300 species in about 100 subgenera and many more are yet to be assigned. Several groups have been split off to form distinct genera e.g. Ocys Stephens, 1828 or Bracteon Bedel, 1879 and this is likely to continue as more molecular studies are performed. More than 250 species occur in the Nearctic region and about 220 in Europe, of which 54, classified in 27 subgenera, occur in the UK so that our fauna represents a reasonable overview of the genus as a whole. The distribution is biantitropical, being replaced in tropical regions by other genera of small carabids, and about 75% of all species occur in the northern hemisphere; southern hemisphere ‘hotspots’ include New Zealand and The Andes. They are among the most common carabids in many situations; many, if not the majority, occur in damp or marginal habitats from mountain streams to lowland fens and marshes etc. to estuaries and the seashore, but many also occur in dry habitats e.g. grassland or agricultural land and some occur in desert regions. Some are confined to certain soil types or habitats e.g. running water, lakeshores or dense riparian vegetation on clay. Many are spring breeders and spring and summer are generally the seasons of maximum abundance, most fly well and overwinter as adults. Many species are common and widespread and are likely to be among the first carabids recorded by the beginner. The genus is very diverse but mostly in fine detail and with a little experience they tend to have a characteristic appearance. All are small carabids, ≤8mm, with a slender forebody and long appendages, resembling smaller versions of Agonum Bonelli, 1810. Most are rather flattened and metallic, drab coloured or with various pale markings or patterns to the elytra. The genus is characterized by the diminutive terminal segment of the maxillary palpi, the notched fore-tibiae and having the base of the scutellum in line with the base of the elytra. The head has a pair of usually well-developed sulci along the inner margin of each eye, these may be doubled and continue
onto the clypeus and in some groups they converge strongly, uniting just behind the labrum. There are two setiferous punctures beside each eye. The elytra have distinct striae, at least towards the base; the sutural striae are not recurved at the apex (cf. Ocys) and the third interstice is normal (cf. Bracteon), bearing two setiferous punctures. Many species have distinctive microsculpture, the form of which can be useful in identification, and this is often more strongly developed in the female. Members of some groups may need to be dissected to determine their identity but as the UK fauna is limited, and as the group includes many excellent diagnostic characters e.g. the form of the frontal furrows, pronotal morphology or the placement of the interstitial elytral pores, this is usually infrequent. Males have the basal segments of the pro-tarsi dilated. The UK fauna includes many widespread and very common species, some of which e.g. B. tetracolum Say, 1823, B. dentellum (Thunberg, 1787) or B. articulatum (Panzer, 1796) will soon become obvious in the field. The following very brief look at the UK subgenera is intended to give an overview of our fauna.
Bembidion pallidipenne (Illiger, 1802), our only representative of the subgenus Actedium Motschulsky, 1864, is a widespread but generally scarce maritime species. The very local riparian species B. lunatum (Duftschmid, 1812), until recently included in subgenus Ocydromus, is now our only member of Asioperyphus Vysoký, 1986. Bembidion S.str. includes 3 species of which only B. quadrimaculatum (Linnaeus, 1760) is widespread and generally common. Bembidionetolitzkya Strand, 1929 includes 4 species of which only B. tibiale (Duftschmid, 1812) is widespread, being more common in the north. B. virens Gyllenhal, 1827 is a very local species of sandy and gravelly waterside habitats in the north of Scotland, for many years included in Trichoplataphus, it is now our only representative of Blepharoplataphus Netolitzky, 1920. Diplocampa Bedel, 1896 includes 3 very local species, B. clarkii (Dawson, 1849) and B. assimile Gyllenhal, 1810 are widespread and may be locally common while B. fumigatum (Duftschmid, 1812) is generally scarce and mostly coastal. Emphanes Motschulsky, 1850 includes two widespread maritime species. Eupetedromus Netolitzky, 1911 includes only the widespread and common B. dentellum (Thunberg, 1787). Our only representative of Lymnaeum Stephens, 1828, B. nogropiceum (Marsham, 1801), is a very local species of the south coast. Metallina Motschulsky, 1850 includes two widespread species of which B. lampros (Herbst, 1784) is generally abundant in dry habitats. B. nigricorne Gyllenhal, 1827, our only member of Neja Motschulsky, 1864, is a widespread but very local and scarce heathland species. B. genei Kuster, 1847, represented in the UK by ssp. Illigeri Netolitzky, 1914, is a locally common species of wetland margins across southern and eastern England and is our only member of Nepha Motschulsky, 1864. B. ephippium (Marsham, 1802) is a very local south-eastern maritime species and is our only member of Notaphemphanes Netolitzky, 1920. Of our 3 species of Notaphus Dejean, 1821, B. obliquum Sturm, 1825 and B. varium (Olivier, 1795) are widespread and may be locally common while B. semipunctatum (Donovan, 1806) is a generally rare species in the south east, all occur in wetland marginal habitats. Ocydromus Clairville, 1806, formerly a much larger group, now includes only 2 widespread but very local UK species. Our 2 species of Peryphanes Jeannel, 1941, formerly included in Ocydromus, are widespread; B. stephensii Crotch, is a generally rare wetland species while B. deletum Audinet-Serville, 1821 is locally common in a variety of habitats. B. (Peryphiolus Jeanel, 1941) monticola Sturm, 1825, also formerly included in Ocydromus, is a rare and local species occurring sporadically in the south of England and Wales and in Scotland. Five species of Peryphus Dejean, 1821, also formerly Ocydromus, occur in the UK, of which at least two are widespread and common, B. bruxellense Wesmael, 1835 occurs in wetlands while B. tetracolum Say, 1823 is abundant in a range of habitats. B. (Phyla Motschulsky, 1844) obtusum Audinet-Serville, 1821 is common and widespread on heavy soils in open situations. Our 6 species of Philochthus Stephens, 1828 are widespread and common in wetland habitats. B. (Plataphus Motschulsky, 1864) prasinum (Duftschmid, 1812) is a very local species of wetland margins across Wales, northern England and Scotland. B. (Princidium Motschulsky, 1864) punctulatum Drapiez, 1812) is a widespread species of sandy and gravelly substrates in wetland habitats. Our two species of Semicampa Netolitzky, 1910 are very local on wetland margins; B. gilvipes Sturm, 1825 is widespread but more common in the north of England while B. schueppelii Dejean, 1831 occurs in northern England and southern Scotland. B. (Testedium Motschulsky, 1864) bipunctatum (Linnaeus, 1760) is a widespread but very local and generally rare wetland species. B. (trepanedoris Netolitzky, 1918) doris (Panzer, 1796) is generally common across the southeast but otherwise less frequent elsewhere except for the far north, it occurs in a range of wetland habitats. Trepanes Motschulsky, 1864 includes 2 species, both of which occur in marginal wetland habitats; B. articulatum (Panzer, 1796) is among the most common species in such habitats across the south of England while B. octomaculatum (Goeze, 1777) is a very rare species of the south and southeast; it was for a long time considered extinct in the UK but since its rediscovery in the early 1990’s seems to be spreading.