Microptilium Matthews, 1872
POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
PTILIINAE Erichson, 1845
M. palustre Kuntzen, 1914
M. pulchellum (Allibert, 1844)
Microptilium Matthews, 1872 is a small genus of two Western Palaearctic species although a further species, M. geistautsi Dybas, 1961, is known from Baltic amber. Both are very rare, they have wide though patchy European distributions and are associated with wetlands and permanently damp deciduous woodlands. Because they are tiny beetles, 0.67-0.77 mm, which for the most part lead concealed lives they are likely to be under-recorded, on the other hand, with a little experience they are very distinctive (at least to genus) and so should be easy enough to recognize among extraction samples etc.
The genus may be recognized by the shape and surface structure of the pronotum but the species are very similar; in general M. palustre is darker, sometimes almost black, while M. pulchellum is lighter, usually pale to mid-brown, but they may be distinguished with certainty by dissection (females) or by a subtle ventral character (males), see below. The following description applies to both species and will allow the genus to be recognized with confidence.
Elongate and discontinuous in outline with the pronotum almost as wide as the elytra, dorsal surface very finely reticulate and with recumbent and slightly overlapping pubescence. Head transverse, broadest across large and weakly convex eyes and smoothly convex above. Labrum with two apical spines, maxillary palpi 4-segmented, the terminal segment swollen internally and the penultimate segment with a small papillate structure at the apex near the insertion of the terminal segment. Antennae 11-segmented and long, reaching back into the basal third of the elytra, two basal segments expanded, third segment not constricted before the base and apical segments long and broadest about the middle. Pronotum wider than the head, transverse, rounded laterally and sinuate just before obtuse posterior angles, apical and basal margins slightly curved, the basal margin narrower than the head, surface with two distinct longitudinal depressions towards the base. Front
Microptilium pulchellum spermatheca
© Arved Lompe
Microptilium palustre spermatheca
© Arved Lompe
coxae closely approximated, not separated by a process, middle coxae separated by a fine keel which extends onto the mesosternum, hind coxae closely approximated and with a very narrow plate on their external margins. Mesosternum about 2X broader than long and extending between the hind coxae. Scutellum smooth, triangular and proportionally large. Elytra elongate and only slightly curved from sloping shoulders to separately-curved apical margins that do not entirely cover the abdomen, surface smooth, finely and randomly punctured and without striae, epipleura bordered by a fine longitudinal keel which may be visible from above towards the shoulders. Abdomen with distinct pygidium and pro-pygidium. Basal ventrite twice as long as the following, with a median elevation that extends between the hind coxae. Legs long and slender, the femora visible in normal setting, tibiae curved internally and without apical spurs. Tarsi 3-segmented, the basal segments short, almost quadrate, and the terminal segment long and slender. Claws slender, smooth and without a basal tooth.
There are no obvious external sexual differences but in males the front tibiae are extended due to a thin pubescent plate and the penultimate tergite has dense fine setae. Females can be identified by dissection; the spermathecae are small, 0.03-0.05 mm, but heavily sclerotized and usually easily seen with good lighting. Males can be distinguished by the form of the metasternal disc; in pulchellum it has a small and shallow depression while in palustre it is flat.
Microptilium palustre Kuntzen, 1914
This very local and extremely rare species has a wide but discontinuous European distribution; it is known from a very few sites in Poland, Denmark, Germany, the Czech Republic, Spain, The Netherlands, Balearic Islands, the UK and possibly southern Sweden, and Gibraltar. Beyond this it does not seem to have been recorded from the Palaearctic region. In the UK it is very local and rare, being known only from the vicinity of Wicken fen in Cambridgeshire. Little is known of the biology but adults have been recorded in May while on the continent they have been recorded in all months from May until august, peaking in abundance during June and July. In the UK they usually occur among damp moss and litter in fens and they sometimes swarm in large numbers, in Europe they occupy similar habitats and have been found in numbers among Sphagnum, in litter, moss and rushes in swamps and along wet inflows, and in Germany they were collected from litter in alder forests and from barrier traps in old oak trees. Adults may be sampled by sweeping or extraction but, at least on the continent, they have often been recorded from window traps in damp wooded areas.
Microptilium pulchellum (Allibert, 1844)
This species is also very local and rare; in Europe it is known from a few sites in France, Austria, Italy and the UK, it is also known from North Africa but is otherwise absent from the Palaearctic region. In the UK it is known from a few sites in East Anglia; near Watton in Norfolk and Mildenhall in Suffolk, and possibly from a further site in Cambridgeshire. Adults have been recorded in the UK during March and April; they occur among moss or decaying litter in fens and marshes, they usually occur in numbers and have occasionally been observed swarming over wetland habitats.