Sphaeridium scarabaeoides (Linnaeus, 1758)
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POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
HYDROPHILIDAE Latreille, 1802
SPHAERIDIINAE Latreille, 1802
Sphaeridium Fabricius, 1775
Generally common throughout the entire Palaearctic region including North Africa and the Near East, it occurs on most of the Mediterranean islands and the Azores and is recorded from the Afrotropical region. The species was introduced Canada and the northern United States in the late 19th century and has since become widely established as far south as Mexico. In Europe it occurs from lowlands to the alpine zone and is generally common except for the far north of Scandinavia, it occurs commonly across England and Wales, including all the islands, and is widespread though much more local in Scotland and Ireland. Adults occur year-round; they overwinter in soil or among moss or decaying vegetation and are active between April and September, peaking in abundance during June and again later in the summer. The typical habitat is dung pasture although adults occasionally occur in herbivore dung in any situation and specimens have been recorded at carrion and decaying fungi. This is an early successional species and is often the first to arrive at fresh dung; it seems that cattle dung is the preferred host material, especially where it is almost liquid, but older horse and sheep dung may also host numbers of adults. Mating pairs are common early in the season and may often be observed upon or within dung samples, eggs are laid directly into the dung where the larvae will develop, predating other insects but especially diptera eggs and larvae. Larval development is rapid and they are usually fully-grown within four weeks, at which time they pupate in a silk cocoon within the host material. In the UK new generation adults appear from early June. Unlike the larvae, the adults are coprophagous although probably more widely polyphagous under certain circumstances. Adults are strong fliers and immature females have been observed to cross long distances to find new host material, they usually arrive at fresh dung earlier than males and are more likely to remain than older females which will often be found among older dung. Both adults and larvae are easily sampled by searching through dung but adults may be attracted in numbers by breaking the crust on slightly older samples and waiting for them to fly in.
The larvae are distinctive, elongate and gradually broadened from a narrow head to a widely-rounded apex furnished with four elongate tubercles, lightly sclerotized and pigmented and only very finely and sparsely pubescent. Head completely fused, with no suture between the head and labrum and the frontoclypeal suture very faint or absent, antennae 3-segmented, labial- and maxillary palps 4-segmented. Mandibular apex with a single tooth. Legs diminutive, each with a single movable claw. Abdomen with 10 visible segments, the 9th tergum entirely dorsal.
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​5.0-7.5 mm. Broadly oval and smoothly convex, glabrous above and with dense hydrofuge pubescence below except on the metasternal disc, colour varies but generally dark with the pronotal margin, often only within the anterior angles, to some extent pale and the elytra with broadly pale apices and often a pale subhumeral marking. Head smoothly convex and extremely finely punctured, broadest across small and rather flat eyes and with strongly converging temples and cheeks. Antennae 8-segmented with a long and curved scape and a densely-pubescent 3-segmented club. Maxillary palpi entirely dark or paler at the apex, about as long as the antennae, with all segments long and slender. Pronotum broadest across distinctly obtuse posterior angles and smoothly narrowed to projecting anterior angles, lateral margins narrowly bordered throughout, surface finely and moderately densely punctured and lacking depressions. In most specimens the lateral pronotal margins are black, becoming reddish-brown anteriorly but this varies. Elytra quadrate or slightly elongate, and smoothly curved from rounded shoulders to a continuous apical margin, basal margin distinctly curved so that, from above, the shoulders are obviously produced forward. Elytral surface finely and rather densely punctured, without larger punctures or striae but with a variously-developed sutural stria in the apical half and often some obscure and very narrow longitudinal lines evident across the disc. Legs substantially pale, the middle and hind always so but usually, from below, with a large dark median area. All tibiae robust and armed throughout with long and sharp spines. Males may be distinguished by the dilated apical segment of the front tarsi.