AEGIALIINAE Laporte, 1840
Of the three British species, one (Aegialia) is widespread, while the other two are very local. Psammoporus insularis is one of our very few endemic beetles.
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Introduction
This is a small group of mostly detritivore scarab beetles including about 80 species in 10 genera distributed primarily in northern temperate regions with a few genera occurring further south, in Australia and South America. Formerly classified as a tribe of the Aphodiinae, this group is now considered sufficiently distinct to warrant subfamily and sometimes full family status, it is divided into two tribes of which the Eremazini Stebnicka, 1977 includes 15 species of the single genus Eremazus Mulsant, 1852, this is a Palaearctic group with most occurring in central Asia; only a single species, E. unistriatus Mulsant, 1851, extends further west, occurring in North Africa and the Canary Islands. The remaining genera are included within the Aegialiini Laporte de Castelnau, 1840 (=Silluviini Landin, 1949). Saprus Blackburn, 1904 includes four species and is endemic to Australia; Tasmania, New South Wales and Victoria. Two monotypic genera are endemic to the Neotropical region, Argeremazus Stebnicka & Dellacasa, 2003 from Argentina, and Amerisaprus Stebnicka & Skelley, 2003 from Chile. The Neotropical fauna otherwise includes a single species of Aegialia Latreille, 1807, A. argentina Martínez, Pereira & Vulcano, 1970. The remainder of the species occur in northern, mostly temperate regions with slightly more than half the total diversity in North America. The classification has recently been revised and several groups formerly classified as subgenera of Aegialia (Psammoporus Thomson, C.G., 1859, Rhysothorax Bedel, 1911 and Caelius Lewis, 1895 and Silluvia Landin, 1949)) are now classed as distinct genera. Caelius includes 5 species of which 4 occur in North America and one, C. denticollis Lewis, 1895, is endemic to Japan. The monotypic Micraegialia Brown, 1931 is Nearctic. Silluvia Landin, 1949, includes 11 species that typically occur at high altitudes in Himalayas and Sino-Tibetan mountains. Aegialia remains the largest genus with 26 species; 22 occur in the New World and 4 are Palaearctic. Rhysothorax includes a single Holarctic species. The Holarctic genus Psammoporus includes 15 species of which 7 occur in the Nearctic region. The European fauna includes 4 species; Rhysothorax rufus (Fabricius, 1792), four species of Psammoporus Thomson, C.G., 1859 including the UK endemic Psammoporus insularis Pittino, 2006, Aegialia arenaria (Fabricius, 1787) and Eremazus unistriatus Mulsant, 1851 which only occurs in the south.
Description
Members are small to medium sized beetles, 1.8-8.8mm (mostly<5,0mm), rather drab brown to black beetles, elongate-oval, flattened ventrally and convex dorsally, generally resembling many species of the Aphodiinae but distinguished by the abbreviated clypeus which leaves the anterior part of the labrum exposed and the robust and strongly sclerotized mandibular teeth. Pubescence variable, mostly fine and inconspicuous dorsally but fine setae are usually visible along the margins of the head, pronotum and elytra, the ventral surface from almost glabrous to densely pubescent. Head moderately large but without horns or exaggerated sexual dimorphism seen in some scarab groups, surface flat or only weakly convex and variously punctured or granulate, frontoclypeal suture usually defined by a narrow dark mark or very fine ridge, clypeus short and exposing the mouthparts, eyes small to moderate in size, only weakly convex and usually not visible from above. Antennae inserted laterally in front of the eyes, the insertions hidden beneath a lateral expansion of the clypeus, 9-segmented with a distinct 3-segmented club. Terminal maxillary palpomere usually cylindrical. Pronotum quadrate to transverse, lateral and basal margins usually bordered, lateral margin often crenulate, posterior angles rounded or obtuse and anterior angles produced. Pronotal surface evenly convex and variously punctured or granulate, sometimes very strongly so. Scutellum small and usually triangular. Elytra elongate and parallel-sided to almost globose, each with 10 variously punctured striae and weakly convex, rarely carinate, interstices. Humeral angle well-defined and usually with a small tooth. In some species the striae may be virtually impunctate and well-impressed only on the disc, fading towards the lateral and apical margins. Abdomen with five or six visible sternites; the pygidium usually without a median transverse ridge or basal groove. Legs variable but usually robust and long. Pro-femur fusiform and relatively narrow, meso- and metafemora broad, flattened and often with series of setiferous punctures. Pro-tibiae robust and often dilated, with 3-5 separate teeth along the outer margin and a slender terminal spur, meso- and metatibiae with several transverse ridges and 2 variable but usually long and well-developed terminal spurs placed either below the tarsal insertions or either side. Tarsi 5-segmented and short or moderate in length, the tarsomeres rarely expanded and at most only moderately elongate. The sexes may differ in the pronotal shape and sculpture, length of the penultimate abdominal sternite or the form of the terminal protibial spur. Many species are fully-winged and are good fliers.
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Ecology
Most species are detritivores associated with decomposing plant material on sandy substrates such inland dunes and sand pits or sand bars deposited by rivers or streams, some are associated with coastal dunes and beaches (Aegialia) while some prefer gravel substrates on stream and pond margins (Psammoporus). Species of Caelius are associated with leaf-litter etc, in boreal or mountain habitats. Some are not associated with any particular substrate but occur among deep leaf-litter in grassland or woodland situations. Most can be sampled by sieving sand, leaf-litter or debris in likely situations, they lead hidden lives but many become active and even swarm during the warmest weather.
UK species
Further Reading
Aegialiini and Eremazini of the World
Z.T. Stebnicka
Provides in depth information on the world fauna.
