Sericoderus Stephens, 1829
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POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
CORYLOPHINAE LeConte, 1852
S. brevicornis Matthews, A., 1888
S. lateralis (Gyllenhal, 1827)
This genus includes about 12 species of minute fungus beetles. The Sericoderini Matthews, 1888 includes two further genera; Anisomeristes Matthews, 1886, with a single species described from the Oriental region, and two species of Aposericoderus Paulian, 1950 described from South Africa. Most species of Sericoderus are very local e.g. S. basalis Sharp, 1885 described from the Hawaiian Islands, S. latus Matthews, 1888 from Central America, and S. minutus Matthews, 1894 from the Caribbean, but a few are more widespread, most notably the almost cosmopolitan S. lateralis (Gyllenhal, 1827). Five species are listed from North America while only three occur in Europe. Of the European species two are widespread while S. pecirkanus Reitter, 1908 is confined to warm and dry parts of Southern Spain and Corsica, it otherwise occurs in North Africa and southern parts of Asia. Difficulty in identification and a general lack of records means that the distribution of the other European species is not well understood, but S. lateralis seems to be locally common throughout the region and it reaches north to the UK and northern parts of Norway and Sweden, while S. brevicornis Matthews, 1890 may have a more northern distribution with records from Germany, Latvia, Finland and the UK, although it is also known from Southern France.
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All species are tiny, 0.8-1.09 mm, but are relatively easy to recognize by general appearance. Body mostly shiny, pale to dark brown, often with darker elytra, entire dorsal surface rather densely pubescent. Head covered by the anterior margin of the pronotum and so not visible from above. Antennae 10- or 11-segmented; the third and fourth segments either free or fused, two basal segments enlarged and about equal in length, and three terminal segments form an elongate club. Pronotum convex and very transverse, more than 2X wider than long, lateral and apical margins smoothly rounded from above, hind angles acute, strongly produced over the elytral humeri and finely rounded apically, basal margin strongly sinuate. Pronotal disc shiny, lateral and apical margins dull. Scutellum triangular and relatively large. Wings fully developed, without a median fleck. Elytra quadrate or slightly elongate, tapering slightly
from rounded shoulders to truncate apical margins, surface very finely punctured and with a variable sutural stria, the sutural interval with two or three rows of punctures. Elytral epipleura narrow at the base and fading beyond the middle. Abdomen with six ventrites; ventrite 1 as long as 2 and 3 together, postcoxal lines absent. Legs short and slender, tibiae without teeth or apical spurs, tarsi 4-segmented but appearing 3-segmented due to the diminutive third segment. Claws simple.
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Regarding our two UK species, identification requires great care and many specimens will need to be dissected and the spermatheca examined. S. brevicornis is sometimes said to be larger and paler than lateralis, but this is of no practical use. Examination of the antennae as well as any dissections should be done with specimens immersed in water, although with good lighting and equipment the antennae can be examined dry. There are several keys available in print as well as online but they tend to give conflicting information and so far the most reliable seems to be that in Volume three of Beetles of Britain and Ireland by Andrew Duff. The following short key includes information from that work as well as other descriptive material:
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1.
Antennae 11-segmented. Metasternum with a small central tubercle. 0.85-1.07 mm.
-S. brevicornis Male
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Antennae 10-segmented, metasternum smooth.
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2.
Sperm duct visible (although only just and sometimes obscurely so) at X25, sperm duct lobe present (X400). Gland duct lobe usually distinctly constricted before the apex. [Body usually uniformly pale to dark brown, antennae pale at the base, legs pale brown.]
-S. brevicornis Female
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-Sperm duct very fine and barely visible at X75, sperm duct lobe absent. Gland duct lobe smoothly tapering to the apex. 0.88-1.09 mm. [Brown to yellowish-brown, often with a dark translucent area at the pronotal apex through which the head is vaguely visible, elytra darker at the base and paler towards the apex. Appendages yellowish-brown.]
-S. lateralis so far known only from females, apparently parthenogenetic.
Both species are associated with decaying vegetation and fungi, especially old and dry bracket fungi on standing trunks and stumps, they sometimes appear in compost or under bark on dead stumps and fallen timber and they usually appear in numbers. Both are capable of flight, and lateralis has been sampled in auto nets on the continent.
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S. brevicornis was first discovered in England in 2006, it now occurs locally across Central and South East England and it appears to be expanding its range. The species was described from Australia and seems to have expanded in recent decades; it was recorded as a pest of Kiwi fruits in New Zealand in 1995 and is also known from California.
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S. lateralis is known from the entire Holarctic region, it is also widespread in Australasia and South Africa but seems to be absent from South America. It is widespread and locally common across Central and Southern England but seems to have declined over recent decades.