Scaritinae | uk beetles

SCARITINAE Bonelli, 1810

These small, distinctive ground beetles are most often associated with wetland or other damp habitats.

ADEPHAGA Clairville, 1806

CARABIDAE Latreille, 1802

2.3-6.8mm

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Introduction

This large and very distinctive group includes almost 1900 described species in 125 genera, it is cosmopolitan in distribution with the greatest diversity in tropical regions and more especially in the southern hemisphere where many genera and groups are endemic to certain areas e.g. the Carenina, a subtribe of the very diverse tribe Scaritini, which includes 11 genera and more than 200 species is endemic to Australia. The group was formerly classified as a tribe of the Carabinae but is now considered sufficiently distinct to form a separate subfamily (as with many other carabid groups formerly considered as tribes), but even so it is probably not monophyletic and various attempts have been made to include other carabid groups such as the unusual Rhysodinae Castelnau, 1840. Various systems of classification are in use; the most straightforward includes four groups considered sufficiently distinct to merit equal status: Clivinini Rafinesque, 1815, Dyschiriini Kolbe, 1880 Salcediini Alluaud, 1930 and Scaritini Bonelli, 1810. In this system various groups are considered as subtribes but other systems generally recognize a more complex system of tribes and the situation becomes difficult although with limited temperate faunas the groups are usually familiar however they are classified. Sometimes the group is divided into two tribes, the Salcediini which includes 4 genera in 3 subtribes and occurs in tropical regions worldwide, and the large tribe Scaritini which includes the remainder classified among (sometimes numerous) subtribes. In the four-tribe system the Dyschiriini is the smallest and probably of most interest to European workers because although it has a worldwide distribution it is most diverse in northern temperate regions. The tribe includes 8 genera of mostly small (up to 8mm) wetland species that disperse by flight. Of particular interest to UK coleopterists is Dyschirius Bonelli, 1810, a worldwide group of about 300 species in various subgenera, of which around 60 occur in Europe and 12 extend to the UK, the generic name is still used for convenience to encompass the group but many of the subgenera have now been re-classified as distinct genera, so Dyschirius s.str. now includes 11 European species and Dyschiriodes Jeannel, 1941 includes 52 species in 4 subgenera which were formerly regarded as subgenera of Dyschirius and of which 3 occur in the UK: Chiridysus Fedorenko, 1996 (3 European spp.), Dyschiriodes Jeannel, 1941 (35 European species) and Eudyscirius Fedorenko, 1996 (12 European spp.). The European fauna otherwise includes 5 species of Reicheiodes Ganglbauer, 1891 which are superficially

very similar to Dyschirius and restricted to southern areas, mainly Portugal, Spain and Italy; the genus is otherwise widespread in Asia with many species endemic to Nepal and Japan. Scaritini is a worldwide group of about 55 genera, it is by far most diverse in tropical areas and includes all the large (>30mm) species, many of which are flightless. The greatest diversity is in Old-World tropical regions with many genera and species endemic to India, Australia, South Africa and Madagascar. The tribe is absent from the UK but represented in Europe by 3 genera. Of the 8 European species of Scarites, 7 have restricted distributions in various Mediterranean areas while one, S. abbreviatus Dejean, 1825 is endemic to Madeira. Distichus planus (Bonelli, 1813) is widespread across southern and western Europe while 3 species of Parallelomorphus Motschulsky, 1850 occur mostly in the south. Clivinini is a large worldwide tribe of about 60 genera, they are most diverse in tropical regions and only poorly represented in northern temperate areas, they are generally smaller (<30mm) than members of the Scaritini and most are capable of flight. Two subtribes are represented in Europe. Eleven genera of the subtribe Reichiina are represented by about 85 species although the majority, about 65 species, are included in Typhloreicheia Holdhaus, 1924. More generally the subtribe includes about 150 species of small, 1-4mm, endogean and hypogean carabids variously adapted to a subterranean lifestyle; the eyes are reduced or absent and most have short moniliform antennae, some species display troglomorphic adaptations and many have a very restricted distribution, the group being most diverse in Mediterranean regions. Clivinina Rafinasque, 1815 is represented in Europe by 8 species of Clivina Latreille, 1802, but only C. fossor (Linnaeus, 1758) and C. collaris (Herbst, 1784) are widespread, extending into Asia and north to the UK, the remainder are restricted to southern areas. Clivina is otherwise very diverse, and is the only cosmopolitan member of the tribe.

Description

All species have the distinctive pedunculate body form and various adaptations to a terrestrial or subterranean lifestyle, among the European fauna members of the subfamilies Siagoninae Bonelli, 1813 and Broscinae Bonelli, 1810 are superficially similar but they lack fossorial tibiae. They vary widely in size, from 1.5mm to about 70mm in some tropical species, the largest European member of the subfamily is Scarites buparius (Forster, 1771) at about 30mm and UK species range from 2.3-7.0mm. The body form is elongate and often rather parallel-sided but otherwise very variable and species range from moderately flattened e.g. in some Scarites Fabricius, 1775, to virtually cylindrical as in various Dyschirius Bonelli, 1810. Most species in temperate regions are dull brown to black and sometimes weakly metallic, as might be expected in an essentially terrestrial group, but some tropical species have strongly-metallic margins to the pronotum and elytra or are otherwise brilliantly coloured e.g. some Dinoscaris Alluaud, 1902 from Madagascar are entirely bright metallic blue. Most are glabrous or nearly so but some troglodyte species have series of very long setae to the lateral margins. Head and prothorax often proportionally large, typically with convex eyes and short temples, vertex variously impressed and antennae inserted laterally before the eyes. Antennae short to moderately long, filiform but often almost moniliform. Mandibles variable, often produced, but always without a lateral seta, massively developed and protruding in some tropical species. Pronotum elongate to transverse and very variable, from globose to flat, with or without lateral borders and various basal fovea or median impressions, typically the lateral margins narrow strongly in the basal half, this may be an adaptation allowing lateral articulation of the body in subterranean habitats. Characteristically the scutellum is located on a relatively narrow peduncle-an extension of the mesosternum-between the base of the pronotum and the elytra. Elytra elongate and rounded to parallel-sided (virtually circular in some tropical forms), shoulders rounded or sloping and often with a small tooth, lateral margins often with a series of punctures but the interstices often lack isolated trichobothria seen in many carabid groups, striae may be well-impressed, punctured and continue to the apex, in extreme cases the elytra may be otherwise smooth, bearing striae only toward the base, interstices flat to weakly convex and usually smooth. In some species the base is narrowly strongly rugose and/or punctured and in some the outer interstices may have dense micropunctures. In general the front legs are much more developed than the others, with enlarged femora and flattened tibia which are armed with external and apical teeth or spines. The middle and hind femora are normally developed but the middle tibiae may also be fossorial, and both the middle and hind tibiae usually bear a long and stout terminal spur. The group includes many species highly evolved for a subterranean or troglodyte lifestyle e.g. Siagona taggadertensis Junger & Faille, 2011, from the Atlas Mountains in Morocco, is large, around 30mm, very slender and elongate with massively developed head and mandibles, long antennae and reduced eyes, while many troglodyte species worldwide are eyeless.

Ecology

Species occur worldwide in a wide variety of habitats from lowland to high mountain altitudes, often on open sandy or loamy soils from coastal dunes to tropical forest habitats, and in some habitats such as sandy beaches of the northern Mediterranean they may be the predominant insect predators. Many inhabit caves or live among forest litter but all are adapted for burrowing; in temperate areas many occur on wetland marginal areas and some are associated with other beetles e.g. in the UK some Dyschirius occur in marginal burrows made by species of the staphylinid genus Bledius Leach, 1819.

UK Fauna

Two species of Clivina are widespread in the UK; C. fossor (Linnaeus, 1758) is generally common throughout, including all the islands north to Shetland, while C. collaris (Herbst, 1784) is much more local and scarce, extending north into the Scottish Highlands and the Hebrides. Of the twelve species of Dyschirius included in the UK list (now variously included in distinct genera) one, D. extensus Putzeys, 1846) was last recorded in 1940 and may now be extinct. D. chalceus Erichson, 1837 has only recently been added, having been formerly confused with the widespread but rare coastal species D. nitidus (Dejean, 1825). Several other species are widespread around our coasts including D. salinus Schaum, 1843, D. thoracicus (Rossi, 1790) and D. impunctipennis Dawson, 1854 while the very rare D. obscurus (Gyllenhal, 1827) occurs in a few coastal sites in the southeast. D. politus (Dejean, 1825) is widespread in the south but coastal in northern Scotland and the Outer Hebrides. D. angustatus (Ahrens, 1830) is very local and rare and known recently from a few sites in southeast England, Cumbria and northeast Scotland. Two species, D. aeneus (Dejean, 1825 and D. leudersi Wagner, 1915, are widespread and locally common in the south but more sporadic and rare elsewhere while D. globosus (Herbst, 1784) is generally common throughout the UK north to Shetland. Our two Clivina species are mostly subterranean, occurring in permanently damp habitats among roots and decaying vegetation although they often occur under debris and may be found on open areas of soil at night, adults occur year-round and sometimes appear in tussock samples during the winter. Dyschirius are generally subterranean, leading cryptic lives below marginal surface sediments or in burrows, many are active on the surface at night but during the warmest weather may also be found wandering among sparse vegetation on wet substrates in bright sun. Our only member of the subgenus Eudyschirius, D. globosus, is common in a range of marginal wetland habitats and may also occur in seasonally flooded environments and permanently wet grassland. Members of Dyschiroides occur in a range of wetland habitats and on various substrates, some in estuarine or riparian situations and some are associated with species of Bledius (Staphylinidae, Oxytelinae) which burrow in soft substrates and on which they predate. Our members of the subgenera Chiridysus (D. extensus) and Dyschirius (D. angustatus, D. obscurus and D. thoracicus) occur on very fine sandy substrates, mostly in coastal situations.

In general species of Dyschirius are smaller (mostly <5mm) than those of Clivina (mostly >5mm) and this is usually obvious in the field but there are exceptions e.g. D. nitidus (Dejean) may be >5.5mm, but in all cases the genera are distinct in the form of the lateral margins of the elytra; in Clivina they have a continuous series of punctures from the humerus to the apex while in Dyschirius the punctures are confined to the humeral and apical areas.

Clivina fossor (top) and Dychirius salinus (bottom).