Anthobium Leach in Samouelle, 1819
Anthobium atrocephalum (Gyllenhal, 1827)
This generally common species is among the most widespread members of the subfamily, it occurs throughout Europe to the UK and northern Fennoscandia and is present in Iceland and across North Africa, it through the Near East, and Ukraine to the far east of Russia and Japan but seems to be absent from many more southern Palaearctic regions including China, it is present on most of the Mediterranean islands and is represented on Sardinia by ssp. sardoum (Scheerpeltz, 1961). With the general exception of the West Country this species is common throughout England and Wales though less so in the north and much more local and rare in Scotland north to the Highland, it is present on Anglesey and IOW but otherwise absent from the islands and is very rarely recorded form Northern Ireland. Adults occur year-round, they are active over a long period from early spring often during mild winter spells, they mostly inhabit leaf-litter in wooded areas but also occur among matted vegetation in damp open grassland and scrub. During the spring they will often be found under logs and debris among leaf-litter but otherwise they will occur among samples of moss or decaying fungi at any time. Little is known of the life history but adults peak in abundance during April and May and pale teneral specimens occur through the summer, they are fully winged and have been recorded at flight interception traps during the spring. They can be sampled by sieving litter or taking samples of tussocks, moss or fungi for extraction but they should occur fairly quickly by general searching in damp woodland.
2.5-3.5mm. Broad and discontinuous in outline with the head much narrower than the pronotum and the pronotum and elytra separately rounded at the base, distinguished by the dark head contrasting with the yellow or pale brown body, legs entirely pale brown, palps and antennal bases pale, distal antennomeres dark. Head transverse with large convex eyes and short temples that protrude slightly behind the eyes and then converge strongly to a short neck, surface quite strongly punctured except for an oblique raised area inside each eye and most of the clypeus, the two ‘ocelli’ near the posterior margins of the eyes distinct due to their paler brown colour. Maxillary palpi
Anthobium atrocephalum 1
Anthobium unicolor 1
Anthobium atrocephalum 2
Anthobium unicolor 2
Anthobium atrocephalum 3
with all segments elongate, the terminal segment pyriform and much longer than the penultimate segment. Antennomeres 1-7 elongate, 8 -10 quadrate or nearly so and 11 pointed and slightly elongate. Pronotum transverse (7:4), the lateral and apical margins rounded and the basal margin straight, surface evenly and quite strongly punctured, without structure but usually with a shallow median furrow, at least in the apical half, explanate and usually paler in colour laterally. Elytra distinctly elongate and more than twice as long as the pronotum, with rounded shoulders slightly wider than the pronotum and narrowly explanate margins that are only weakly dilated towards a continuously rounded apical margin that leaves three or four abdominal tergites exposed. Surface mostly randomly punctured but traces of striae are obvious, at least on the inner half where there may also be incomplete longitudinal impressions. Legs short and slender, the femora only narrowly visible in normal setting, all tibiae with fine but distinct spines towards the apex and very fine apical spurs. Tarsi 5-segmented, the third and fourth segments of the middle and hind tarsi narrow but distinctly bilobed, the basal segments of the front tarsi much more broadly so, claws narrow, smooth and without a basal tooth. Males can be distinguished by the middle tibiae which are thickened in the apical half, and the front tibiae which are weakly but distinctly angled along the inner margin.
Anthobium unicolor (Marsham, 1802)
This species has a much more restricted Palaearctic distribution, it is a mostly western and central European species; in the south it is present in Portugal, Spain and France but otherwise absent from the Mediterranean countries, it is common in central Europe and to the north extends sporadically to Denmark, where it is generally common, Poland, where it is very rare, and into southern parts of Fennoscandia where it is very local, it is present in Belarus but absent from the Baltic region in general and the southern extent of its distribution is Switzerland and Austria. The UK distribution is similar to that of atrocephalum, being generally absent from the West Country but extending further north, to the Hebrides and Orkney and it is more widespread in the north of Ireland, it is locally common throughout and the two often occur together. Adults occur year-round, they are usually active through the winter and they peak in abundance in the spring, teneral specimens occur in the summer and autumn and may be extracted from tussocks and litter etc. The typical habitat is damp woodland and other shaded situations, they usually occur among tussocks, litter or decaying fungi on logs etc but during the spring (when they seem to disperse by flight) they sometimes occur when sweeping low herbaceous vegetation in open woodland or other shaded places. Adults may occur over a wide local area but except during warm days in early spring they rarely appear in numbers.
3.0-3.5mm. Broadly oval and discontinuous in outline, entirely pale reddish-brown or yellow, sometimes with the head obscurely darker but never black, legs pale brown, antennae pale at the base and gradually darkened distally. Head transverse with large convex eyes and short protruding and strongly converging temples, vertex finely punctured throughout and with an oblique impression in front of two pale ‘ocelli’. Second segment of the maxillary palps only slightly elongate, terminal segment long and rounded apically, Antennomeres 1-9 elongate, 10 quadrate and the terminal segment elongate and rounded apically. Pronotum transverse (almost 2:1), broadest near the middle and smoothly narrowed to rounded anterior angles and very slightly protruding posterior angles basal margin straight, anterior margin curved forward, surface weakly convex, explanate laterally and quite strongly punctured throughout. Elytra quadrate or only very slightly elongate, more than twice the length of the pronotum, with sloping shoulders and distinctly dilated towards separately rounded apical margins which leave four or five abdominal tergites exposed, surface smoothly convex and narrowly explanate, the punctures mostly random; seldom forming obscure longitudinal series. Legs short and slender, the tibiae hardly broadened from the base, all tibiae with short spines along the dorsal and external surfaces and short, inconspicuous apical spurs. Tarsi 5-segmented; middle and hind tarsi with segments three and four bilobed but narrow, front tarsal segments 1-4 bilobed and slightly expanded compared with the long terminal segment. Claws small and curved, smooth internally and with at most a very small basal tooth. Males have an angle on the inner margin of the front tibiae but the inner margin of the middle tibiae is straight.
Our two species are readily identified by the colour of the head but teneral specimens are entirely pale and can be difficult to separate. In unicolor the pronotum is more transverse, it lacks a median furrow and the lateral margins are slightly sinuate before the posterior angles, the elytra are less elongate and more randomly punctured, the punctures are also a little stronger but this can only be appreciated by comparing a series of each species. The middle tibiae are simple in the male i.e. they are not thickened in the apical half as seen in atrocephalum.