Omonadus formicarius (Goeze, 1777)
Native to the western Palaearctic region, this species is locally common throughout Europe from the Mediterranean to the far north of Fennoscandia, it occurs on all of the Mediterranean islands, and across North Africa the Near East and into Western Russia, in the UK it is very local across southern and central England, absent from much of the West Country and sporadic and scarce through Wales and further north to Southern Scotland. Adults are often synanthropic and have occasionally been recorded among stored products such as various grains and so have been transported widely with trade; it had been recorded in the United States since the late 19th century and is now established and widespread in the wild, more generally it is near cosmopolitan and known to be established in e.g. South and Central America, Australia, Canada and on many oceanic islands. Adults occur in a very wide range of habitats, often on open grassland and scrub but they are common in parkland, gardens and disturbed areas generally, they are sometimes common around coastal lagoons and cliffs and often occur on wetland margins, including salt marshes, they are present year-round and active over a long season from March or April. Breeding occurs in the summer and larvae develop among decaying plant material, they are mostly scavengers, feeding on the products of plant decay and fungal hyphae and spores but will also opportunistically predate small insects and other arthropods; they pupate in the ground or among the host material and new-generation adults occur in the summer. Adults will sometimes occur among sieved samples of compost and decaying leaf-litter but they are mostly diurnal and may be found on flowers or swept from vegetation, on hot sunny days they sometimes bask on fences or foliage and they fly above vegetation late into the evening, sometimes appearing in light or flight-interception traps; they usually occur singly or in small numbers but occasionally large numbers may be found in a small area of umbels or other flowers.
Omonadus formicarius 1
2.5-3.7 mm. Elongate, flattened and discontinuous in outline, head and pronotum with very fine but distinct microsculpture, upper surface shiny; head dark reddish-brown, sometimes extensively black, pronotum and basal third of elytra brown, apical two-thirds of elytra dark brown or grey, sometimes the elytra are more extensively dark with pale markings only below the shoulders, legs pale or with femora darker towards the apex, antennae pale but usually with the middle segments darkened, sometimes extensively dark with only the basal segments pale. Entire dorsal surface finely punctured and with short recumbent pubescence. Head transverse with large convex eyes, long and rounded temples and a widely truncate basal margin, surface rather flat and without sculpture except for a variously-developed baso-medial depression, clypeus produced in anteriorly, and terminal maxillary palpomere long and slender. Antennae inserted laterally in front of the eyes, 11-segmented; basal segments elongate, 7 & 8 quadrate, 9 & 10 slightly transverse and 11 elongate and pointed. Pronotum quadrate, broadest behind a rounded anterior margin and narrowed to rounded posterior angles, surface evenly convex, sometimes depressed in front of the basal margin but otherwise without sculpture. Elytra elongate and broadest behind the middle, with rounded shoulders and an almost continuous apical margin, without any trace of striae. Legs long and slender, femora unarmed, tibiae straight and only weakly broadened from the base; middle and hind tibiae with a short and very fine apical spur, tarsi 5-5-4, the penultimate segment deeply bilobed, claws smooth and not toothed at the base.