ALEXIIDAE Imhoff, 1856
No Common Name
A local species of southeast England which may occasionally occur when sweeping grassland or sampling decaying vegetation.
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
Sphaerosoma Stephens, 1832
S. pilosum (Panzer, 1793)
1.4-1.7mm
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Introduction
This is a small family containing about 55 species included within the single genus Sphaerosoma Samouelle, 1819. It is restricted to the Western Palaearctic including most of Europe, Asia Minor and North Africa with the greatest diversity in the Mediterranean area. Several species have a very restricted distribution e.g. S. corcyreum Reitter, 1883 from Corfu, S. subglabrum Normand, 1936 from Tunisia or S. reitteri (Ormay, 1888) from Transylvania while others, including our only U.K. representative, are widespread in Europe. All the species are small, 1.2-1.7mm and globular in appearance; highly convex and rounded, either more or less continuous in outline or with the pronotal base wider than the elytra. They are drab insects, black to pale brown with little or no pattern or contrast in colouration. The dorsal surface is finely to coarsely punctured and generally pubescent, usually rather sparsely so but sometimes densely and occasionally e.g. in the European S. globosum (Sturm, 1807), more or less glabrous. The head is transverse and mostly hidden under the pronotum, with small but prominent eyes and a distinct Frontoclypeal suture. The antennae are 10-segmented with a well developed and usually broadly elongate club. The palps are much shorter than the antennae and generally not visible from above, the terminal segment of both the maxillary and labial palps are securiform. The pronotum is broadest at the base and roundly narrowed around the anterior margin, from above the hind angles appear acute, and the basal margin is sinuate. The scutellum is relatively large and often more shiny than the surrounding cuticle. The procoxal cavities are open inside, the mesocoxal cavities open laterally and the metasternum has strongly curved postcoxal lines. The elytra completely cover the abdomen and are rounded or weakly acuminate at the apex, the surface varies from finely to coarsely but shallowly punctured and variously pubescent. The legs are slender and relatively long; the femora generally visible from above, the tibiae only weakly broadened towards the apex and lacking any lateral spines. Tarsi 4-4-4; the second segment of the meso- and metatarsi is lobed beneath. Wings usually absent.
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So far as is known all species feed upon terrestrial fungal fruiting bodies among leaf litter and moss etc. both as larvae and adults.
Sphaerosoma pilosum (Panzer, 1793)
This seems to be a very local U.K. insect with records scattered across southeast England and a single remote record from the northeast (NBN), although given its small size and dark colouration it is probably very under recorded. Locally, in South Hertfordshire, we have recorded the species repeatedly from decaying vegetation on calcareous grassland during July and August, and from an extraction sample of fungus taken from a dead horse chestnut stump during September in a Watford park.
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Needless to say, the species needs to be searched for very carefully and probably the best way to record it is to take samples of decaying vegetation for extraction; searching in the field is very difficult as there are other very small species e.g. hydrophilids and cryptophagids which are superficially similar and common in the same habitat.
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1.4-1.7mm. Short-oval and convex, continuous in outline and dark brown to almost black, in some specimens the head and pronotal margins are pale. The entire dorsal surface has sparse long and grey or yellowish pubescence. All appendages pale. Head quadrate although mostly hidden under the pronotum, vertex flat to weakly convex, frontoclypeal suture distinct and the anterior margin of the labrum flat or weakly concave. Eyes small but very prominent and with large facets. Antennae inserted in front of the eyes; segments 1 and 2 elongate and broad, 3 elongate and narrow, 4-7 quadrate or nearly so and 8-10 form a distinct club. Head and pronotum shiny and very finely punctured. Pronotum broadest at the base, hind angles weakly obtuse, lateral margins straight and contracted to rounded and weakly protruding front angles, anterior margin strongly convex (view obliquely from in front). Lateral margins finely bordered. The scutellum is small and in some specimens hidden by the pronotum. Elytra shiny, randomly and much more strongly punctured than the pronotum, and finely bordered laterally. The lateral margins and apex are not visible from above due to the convexity. Epipleurs broad and parallel almost to the apex. Legs relatively long; tibiae weakly broadened towards the apex, sometimes weakly sinuate externally, and without spines. Tarsi 4-4-4. Two basal segments on all tarsi lobed beneath. Claw segment long and weakly curved, claws smooth and not toothed at the base.