Microscydmus Saulcy & Croissandeau, 1893
Microscydmus is a cosmopolitan genus of almost 200 described species although this number is likely to increase greatly as the group is revised, at present it includes 5 subgenera; Microscydmus s.str. is cosmopolitan and includes the majority of the species, Neladius Casey, 1897 and Delius Casey, 1897 are Nearctic and each includes a single species, Neoscydmus Franz, 1980 includes 9 Neotropical species, and Parastenichnus includes 2 Oriental species. The genus is most diverse in warmer regions and temperate faunas are small; 5 are known from the Nearctic region and only 3 occur in Europe. Two of the European species are widespread and extend to the UK while the third, M. stocki (Sainte-Claire Deville, 1914) has an unusual distribution and is recorded from France, including Corsica, and Sweden. So far as is known all species are associated with decaying trees or leaf-litter in old established woodland and it is likely that because of their small size and cryptic lifestyles all are under-recorded.
Species are very typical of the subfamily, elongate and discontinuous in outline, finely punctured and pubescent (the pronotum often more densely so than the elytra) and pale to dark brown dorsally. 0.7-0.9 mm. Head large but usually distinctly narrower than the pronotum (in M. nanus sometimes only slightly so),eyes large and placed towards the front margin, temples long and strongly converging to a narrow neck (at most half as wide as the head), second maxillary palpomere narrow and weakly elongate, terminal segment well-developed and slender. Antennae inserted on the forehead in front of the eyes, 11-segmented with two large and elongate basal segments, the first of which is entire and not incised apically, and a distinct and loose 3-segmented club. Pronotum distinctly narrower than the elytra, quadrate or slightly elongate, broadest about the middle and narrowed to distinct posterior angles and rounded or angled anterior angles, surface evenly convex but for a transverse series of impressions before the basal margin. Hind coxae narrowly separated and widely transverse, reaching the elytral margin or almost so. Elytra long-oval and smoothly curved from sloping shoulders to a continuous apical margin which completely covers the abdomen, surface evenly convex but for two deep fovea across the base of each. Legs long and slender, femora unarmed, tibiae only slightly broadened from the base, more or less straight and without obvious terminal spurs. Our UK species can be identified as follows:
Microscydmus nanus 1
Microscydmus minimus 1
Microscydmus nanus 2
Larger, 0.75-0.90 mm. Usually dark brown, sometimes almost black, with contrasting pale brown or yellowish appendages. Eyes more convex and prominent. Antennae more elongate; the second segment almost 2X longer than wide and the club long and loose although shorter than segments 3-7 combined. Pronotum quadrate, broadest slightly behind the middle and strongly narrowed to distinct obtuse anterior and posterior angles, surface with four equal sized and closely-spaced fovea in front of the basal margin. Elytra with elongate and well-defined humeral calli and a broad impression which extends back towards the basal margin.
Smaller, 0.65-0.80 mm. Pale brown to yellowish-brown with slightly paler appendages. Eyes less convex and prominent. Antennae more compact; the second segment about 1.5X longer than broad, and segments 3-8 combined equal to or very slightly longer than the loose and elongate club. Pronotum quadrate, broadest about the middle and more evenly curved to rounded anterior angles and obtuse posterior angles, surface with four unequal fovea in front of the basal margin; the inner pair much stronger than the outer pair. Elytra each with a weakly defined humeral calli and a round basal impression.
M. nanus occurs throughout Europe from France to Italy and Hungary in the south and extending north to the Baltic countries where it reaches the Arctic Circle in Sweden. it is generally very local and rare except for a few areas in Central Europe and across the south of Norway, Sweden and Finland where it appears to be locally common. The species is widespread but very local and rare in the UK; it is known from widely scattered sites across Southern and Central England and Wales, extending north to Yorkshire although there are unconfirmed records further north as far as Newcastle. The usual habitat is ancient deciduous woodland and wooded pasture and adults occur under bark or among surrounding leaf-litter and moss. Adults occur throughout the year; they are active from April until October, and peak in abundance in early spring and again in early summer, they spend most of their time among the substrate and are active in the open only on the warmest of spring or summer days. Little is known of the biology but both adults and larvae probably predate various mites, as is usual in the group.
M. minimus is probably the most widely distributed of the European species; it extends from France to Italy and Greece in the south and reaches north into the UK, Denmark and the Baltic countries where it reaches the Arctic Circle in Sweden. The species is generally very local and rare and seems to be locally common only across the south and east of Sweden, records from the other Baltic countries being very sparse and infrequent e.g. it is known from only four sites in Poland. In the UK this is a very rare species known from only a few sites in Southern and Central England although there are more widespread but unconfirmed records from around Manchester. The typical UK habitat is old established deciduous and mixed woodland, wooded pasture and undisturbed parkland although the species may occur in individual ancient trees growing in hedgerows etc. More generally it has been recorded from a range of deciduous trees and occasionally from conifers. Adults are present year-round and peak in abundance during June, they usually occur among mouldy wood fragments in cavities in old Oak and Beech trees or stumps but they also occur among litter and moss and, on the continent, have been found in ant (Lasius spp.) nests. Little is known of the biology but it is likely to be typical of the group and similar to the previous species.