Cytilus sericeus (Forster, 1771)

This is one of the most common members of the family in central and northern Europe; in the south it extends from Spain to Northern Italy and then sporadically further east to Greece and Ukraine, here it is more generally a mountain species which has been recorded up to 2400 m in the Alps but further north it is more widespread and occurs from lowlands to mountain altitudes, it extends to the UK and the far north of Fennoscandia and is also present in Iceland. Further east it occurs across the Palaearctic region from Turkey to China, South Korea and Japan, and it is also native to North America. Throughout lowland Europe the species is parthenogenetic; males are rare and recorded only from mountain regions. In the UK it is locally common throughout England and Wales, including the islands, and more sporadic and scarce to the north of Scotland, including the Hebrides, and Northern Ireland. Adults are unusual among the family in that they are diurnal and will often be seen wandering on pathways or climbing grass stems in bright sunshine, they occur in a wide range of both dry and damp habitats such as wetland margins, moorland, floodplain grassland, dunes and open woodland and they often occur among mossy debris on disturbed wasteland, arable margins and gardens, on open moorland they are often common among litter under matted heather foliage and they may appear in pitfall traps in most situations, adults are known to fly but they have rarely been seen to do so. Adults occur year-round and are active from March or April until September, they overwinter among moss and litter and generally become active during the first warm spring days. Both adults and larvae are known to feed on various mosses; adults may be found grazing on soft leaves while larvae live among stems and growth near the soil, often among Polytrichales, they are agile and can run rapidly among the stems  and are unusual among byrrhid larvae in that they do not burrow but feed mainly on rhizoids on the surface although they do pupate in the soil, analysis of larval gut contents has revealed fragments of mosses, liverworts and other vegetation as well as fragments of heather leaves and stems suggesting that they are detritivores rather than specialized moss feeders. Adults and larvae peak in abundance during May and June, adults are known to overwinter and it is likely that at least some larvae do also as they have been found in November. Sampling is usually by searching through mossy debris, under heather is often productive, but they need to be looked for very carefully as when disturbed they retract their appendages and remain still for some time, they may also be found by chance roaming the surface or climbing stems during warm weather.