Poecilium alni (Linnaeus, 1767)
POLYPHAGA Emery, 1886
CHRYSOMELOIDEA Latreille, 1802
CERAMBYCINAE Latreille, 1802
CALLIDIINI Kirby, 1837
POECILIUM Fairmaire, 1864
This locally common species occurs throughout Europe from France north to southern Fennoscandia and the UK, south along the Mediterranean and east to the Urals, here it is widespread though local across southern and central England north to the Humber, rare and sporadic further north to the Scottish border but generally absent from Wales and the West Country. The typical habitat is open deciduous woodland and woodland margins but it also occurs on isolated trees on heaths and disturbed ground in urban situations, adults are diurnal and active over a long season, usually between April and July and peaking during May and June, but often later depending on the season. Mating occurs in spring and early summer and females oviposit among bark on damaged or weakened trees or fallen timber, usually on branches between one and seven cm in diameter. Freshly emerged larvae tunnel through the bark and create winding galleries as they feed, they continue to feed into the autumn and winter and when fully grown excavate a chamber in the xylem where they will pupate in the spring. The life cycle is thus completed over two years but under unfavourable conditions the larval stage may extend over a further year. A wide range of deciduous species have been recorded as hosts, they are most often recorded from oak but also from willows, hazel, alder, elm, ash and chestnut etc. Adults may be seen in numbers flying around shrubs or fallen timber but they are also easily spotted as they rest on trunks or logs, and beating or sweeping foliage will often produce them.
This small and very distinctive longhorn should not be mistaken for any other UK species. 4-7mm. Head, pronotum and scutellum black, elytra black with the basal third red and two pale transverse marks across each, entire dorsal surface pubescent, that on the foreparts longer and sparser, on the elytra short and recumbent but for two groups of longer hairs behind the scutellum. Appendages pale or the femora may be darker. Head and pronotum quite strongly punctured; head transverse from above, with very deeply incised eyes and long antennae, the third segment of which is longer than the fourth. Pronotum transverse; usually more strongly so in the male, evenly rounded laterally and constricted just before the base, colour usually entirely black but often with the anterior and basal margins narrowly red. Elytra elongate, flattened dorsally and impressed inside the shoulders, slightly dilated after the middle and separately rounded apically. Legs long and robust; all femora broadly expanded towards the apex, middle tibiae distinctly curved and all tibiae with a small spur at the inner apical angle. Tarsi short and slender, the basal segment of the hind tarsi about as long as the next two combined. Males are readily distinguished by their longer antennae, more transverse pronotum and less elongate elytra.