Millidium minutissimum (Ljungh, 1804)
POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
PTILIINAE Erichson, 1845
Millidium Motschulsky, 1855
Formerly known as Ptilium exaratum (Allibert, 1844), and widely referred to as such in older literature. This is a very widespread Palaearctic species, it occurs across North Africa and Asia Minor and extends into the far east of Russia, in Europe it extends from the Pyrenees to Greece in the south and north to the UK and far above the Arctic Circle in Scandinavia, it is locally common in southern and central regions but declines further north. It is thought to have been introduced into the United States where it is widely established (Illinois, Washington and Wisconsin), and was first recorded from Canada in 1970. In the UK it is generally scarce and known from only a few widely scattered records in England and North Wales. Adults have been recorded throughout the year and, in Northern Europe at least, they are common from May until August with numbers falling sharply in September. The usual habitat is among decaying leaf litter and moss but adults are often associated with older and dry dung samples, manure and compost, and on the continent they sometimes occur in decaying fungi. Nothing seems to be known of the biology but, despite being very local and scarce, adults are often abundant where they occur and sometimes swarm in very large numbers on warm summer days.
0.60-0.65 mm. Elongate and discontinuous in outline, body shiny, with sparse pubescence and distinct reticulate microsculpture, dark brown or paler towards the elytral apex, antennae brown but darkened apically, legs pale reddish-brown. In many specimens the head and pronotum are distinctly darker than the elytra. Head (from above) widely rounded in front of weakly convex eyes that normally touch the pronotum, surface convex and weakly wrinkled. Antennae inserted anteriorly and widely spaced, 11-segmented, two basal segments much broader than 3-8 which are elongate, and 9-11 form rather gradual and loose club. Pronotum transverse and broadest about the middle, smoothly rounded anteriorly and sinuate before obtuse posterior angles, surface with a broad and deep longitudinal median furrow which ends before the apical margin and two longitudinal basal furrows that do not extend beyond the middle. Scutellum triangular, with a deep central furrow and well-impressed lateral fovea. Mesosternal keel not reticulate, and hind coxae widely separated. Elytra as broad across the base as the base of the pronotum and evenly curved to a continuous apical margin that completely covers the abdomen, surface without striae or distinct impressions, the surface shiny and with a fine leathery texture. Wings very long, with a complex folding mechanism and very long apical setae. Legs short and slender, the tibiae only weakly broadened from the base and without obvious apical spurs. Tarsi 3-segmented; the two basal segments short and much broader than the very long and slender apical segment.
Very similar to species of Ptilium Gyllenhal, 1827 but distinguished by the broad and deep central furrow to the pronotum.