Cossonus linearis (Fabricius, 1775)

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POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

CURCULIONIDAE Latreille, 1802

COSSONINAE Schönherr, 1825

COSSONINI Schönherr, 1825

Cossonus Clairville, 1798

A locally common species throughout Central and Southern Europe, also known from Gibraltar and many of the Mediterranean islands but absent from North Africa, to the north it extends sporadically to the UK, Denmark and the Southern Baltic countries, it is known from the extreme south of Sweden but is otherwise absent from Fennoscandia, and to the east it extends through Asia Minor, Russia and Kazakhstan into Mongolia and Western Siberia. In the UK it is very local and generally scarce although it seems to be expanding its range, at present it is widespread across East Anglia and there are scattered records from the South East and the Midlands but a recent record from the Cornish coast would suggest a much wider occurrence. Typical habitats are humid deciduous woodland and parkland with plenty of trees in various stages of decay but they may occur in carr and on individual trees in suitably damp grassland and moorland etc. or on wetland margins. Adults occur year-round, peaking in abundance during May and June; they are active from March until August or September and are strictly nocturnal, usually occurring on damaged trunks or fallen timber and often in numbers. A wide variety of broadleaf trees have been recorded hosting the species and they sometimes, though rarely, occur on conifers in mixed woodland, but by far the commonest hosts are various poplars (Populus L.) and willows (Salix L.). Mating occurs in the summer and larvae develop among damp decaying wood in trunks and stumps, it is likely they overwinter as teneral adults have been recorded in June. Nocturnal searching is probably the best way to find adults as they feed on decaying wood and often crawl (and they will run quickly and readily enter crevices when disturbed) on the surface of logs etc., by day they hide under bark and in crevices and occasionally, especially during May and June, occur in groups of fifty or more specimens.

Cossonus linearis

Cossonus linearis

4.0-6.0 mm. Elongate and discontinuous in outline with a small head, rounded pronotum and parallel-sided elytra, glabrous and flat dorsally and with a distinctive rostrum. Colour varies, most specimens are pale to dark brown but the head is often darker than the rostrum and the rest of the body. Vertex convex and very finely punctured, sometimes appearing almost smooth, frons densely and moderately strongly punctured between weakly convex eyes, rostrum punctured throughout, dilated and sub-parallel apically. Antennae inserted towards the rostral apex, the scape strongly thickened towards the apex, funiculus with seven transverse segments and the club broad and pointed. Pronotum slightly elongate, broadest about the middle and curved to rounded posterior angles and a weak subapical constriction, surface strongly but not densely punctured, those across the base at least as strong as those beside the disc and usually distinctly stronger. Scutellum small but easily visible. Elytra parallel-sided from rounded shoulders to a continuous apical margin, striae strongly and regularly punctured from the base and interstices smooth, convex and about as wide as the striae. Legs long and slender with widely separated coxae (by about 2/3 the coxal diameter) and smoothly clavate femora, tibiae expanded from the basal third and with a long apical tooth that is continuous with the external margin. Tarsi slender, the third segment hardly wider than the second segment and the apical segment long and curved, claws smooth and well separated at the base.

Similar to C. parallelepipedus but here the dorsal surface is slightly convex, the punctures across the pronotal base are at most only slightly larger than those beside the disc, and the elytral interstices are wider than the striae and the front coxae are separated by about half the coxal diameter.