Hololepta plana (Sulzer, 1776)
First recorded from the UK in 2009 from several specimens found under poplar bark in West Norfolk, this species has since spread widely in the southeast of England and is continuing to expand its range, it is primarily associated with poplars in woodland and wooded parkland but may be found on fallen timber in a wide range of situations including urban areas. The wider distribution includes almost the entire Palaearctic region, in Europe extending from the Mediterranean north into central Fennoscandia where it is associated with various deciduous trees but especially Populus tremula L. (aspen), P. alba L. (white poplar) and the cultivar P. alba ‘Pyramidalis’, and in northern regions it is occasionally found under pine bark. Adults are present year-round and are almost always associated with fallen timber, usually branches but sometimes on logs lying on the ground, they are active from April until late in the summer and are nocturnal although they may be found active and even fly in hot weather. Both adults and larvae are predatory, larvae live under close-fitting bark and adults generally remain under bark during the day but may be observed on the surface at night as they move run rapidly in search of prey, exploring the wood with their antennae held forward and sweeping from side to side as they go. On the warmest nights adults may also occur in light traps, often carrying phoretic mesostigmatid mites. Because adults spend much of their time under close-fitting bark they are probably under-recorded and given time this species will almost certainly become widespread and common in the UK, as it is in suitable habitats throughout Europe.
The large size and much flattened form make this species unmistakable among our UK fauna. 8.0-9.0mm, entirely shiny black with the antennae and tarsi variably red. Dorsal surface smooth and glabrous and mostly impunctate. Head transverse with small reniform eyes that are only narrowly visible from above and long smooth mandibles that project forward, antennae 11-segmented; the scape sinuate and gradually broadened from the base, basal funicular segments elongate then progressively shorter and more transverse, club long oval with margins of all segments distinct. Pronotum widely transverse, rounded laterally and broadest about the middle, anterior angles strongly produced either side of a straight anterior margin, surface smooth but for a variously-developed longitudinal impression in the basal half. Elytra smooth, with only a single short stria above the humerus and several ill-defined impressions along the basal margin, lateral margins more or less parallel and apical margins strongly converging. Pygidium and propygidium widely visible beyond the elytral apices, both sparsely and moderately strongly punctured, especially laterally. Femora short and only narrowly visible from above, tibiae widely expanded towards truncate apices, all with strong external teeth and a long spur at the inner apical angle.