Polydrusus cervinus (Linnaeus, 1758)
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
POLYDRUSINI Schönherr, 1823
This species is generally common throughout Europe from the Mediterranean north to the UK and central Fennoscandia, it reaches east into western Siberia but is absent from the southern Asian countries, it is present in the Channel Islands, Azores, Canary Islands, Gibraltar and the Balearic Islands but absent from North Africa, it is also recorded from the Faroe Islands and Iceland and has become established in eastern North America following introductions from Europe. In the UK it is common throughout England and Wales and very local and scarce further north to the Scottish Highlands. Adults occur from April until August in deciduous woodland and wooded parkland etc. they feed on the foliage of a range of trees including hazel, cherry, poplar, sycamore, alder, oak, and willow but will almost always be found on birches, they have also been recorded from hawthorn and roses and in the spring will sometimes be common on hawthorn blossom. They are diurnal and they fly well and so may suddenly appear in well-worked sites, mating occurs in the spring and pairs will often be found among foliage or on blossom. Eggs are laid in the soil among roots of the host, cock’s-foot grass (Dactylis glomerata L.), and larvae develop in the soil feeding on the roots, they move deeper into the soil in the autumn to overwinter and ascend to continue feeding in the spring, pupation occurs in a cell below the surface during March or April and adults emerge a few weeks later and fly to host foliage to begin maturation feeding. Adults will appear sooner or later when sweeping birch foliage, they tend to be present in numbers on individual trees or on only a few trees even when many are present, and they seem to show no preference as to which trees to attack, from seedlings to fully mature trees.
3.5-5.7 mm. The typical elongate-oval form and tessellated pattern of scales to the elytra will soon make this species very distinctive in the field. Body black with fine decumbent pubescence and patches of golden, bronze, greenish or silvery scales, these are dense on the forebody and usually form longitudinal series of patches along the elytra but this is variable and specimens quickly become worn. Head moderately convex and rather densely scaled between convex and protruding eyes, temples long and almost parallel, rostrum quadrate to weakly elongate and narrowed towards the apex, smooth between the antennal insertions (i.e. without a transverse ridge) and with lateral scrobes that are angled down in front of the eyes. Antennae long and slender, pale but variously darkened apically, the scape gradually and only weakly thickened from the base, all funicular segments elongate and the club narrow, long and pointed. Pronotum transverse, broadest about the middle narrowed to distinct angles, surface evenly convex and densely scaled. Elytra with broadly-rounded shoulders, much wider across the base than the base of the pronotum, narrower and almost parallel-sided in the male, dilated behind the middle in the female, with narrow impressed and punctured striae complete to the apex and broad flat interstices. Legs long and robust, the front femora with a distinct ventral tooth, tibiae extensively dark but always with the base red, sometimes very narrowly so, tarsi pseudotetramerous with the third segment widely bilobed, claws fused at the base.