Strophosoma melanogrammum (Forster, 1771)
This is a generally common species throughout Europe from the Mediterranean, including Morocco as the only African country, to southern Scandinavia and east to Asia Minor, Turkey and western Russia; here it is locally common throughout mainland UK and extending to most of the islands including Orkney but not Shetland. Beyond this native distribution it is an established adventive in the northern United States and Japan. Typical habitats are broadleaf woodland, wooded parkland and scrub etc. although in Scandinavia it also occurs in conifer plantations where large populations may cause serious damage to pine (etc.) seedlings and young trees. Adults occur year-round, peaking in late summer or early autumn, and are active over a long season from spring into late autumn, they are widely polyphagous and have been observed feeding on the foliage of various grasses e.g. Agrostis capillaris L., Carex hirta L. and Festuca rubra (L.), herbaceous plants e.g. Geranium pusillum L. and Erodium cicutarium (L.) and a diverse range of trees and shrubs e.g. Cytissus scoparius L. and Prunus laurocerasus L. and many broadleaf trees but Quercus and Corylus seem to be preferred, the common name refers to its status as a pest of Corylus plantations on the continent. In the UK it appears to be parthenogenetic as males have not been found but both sexes occur on the continent where mating begins in the spring following a period of maturation feeding; here overwintered adults emerge in early spring and feed on buds and young foliage for a while before oviposition begins. Eggs are laid in small batches which the adult covers in a layer of mucus, they are often laid in soil crevices around host plants but also in crevices in stems, among leaf litter or in leaf or flower axils, oviposition continues over a long season but larvae appear from mid or late spring. Freshly emerged larvae enter the soil and feed upon fine roots until the third or fourth (final) instar when they will either pupate or overwinter to continue feeding and pupate in the spring. Larvae from early laid eggs pupate from August and produce new generation adults from September; these will leave the soil and ascend stems to feed before returning to overwinter. Adults will be found by general sweeping or beating of trees and shrubs but they are also nocturnal and will be found active on tree trunks through the summer, they will also occasionally occur among extraction samples of moss and bark etc.
Strophosoma melanogrammum 1
Strophosoma melanogrammum 2
Strophosoma melanogrammum 3
Strophosoma melanogrammum 4
This weevil soon becomes obvious in the field; the globose form, dull-metallic colour and glabrous shiny cuticle at the base of the elytra are characteristic, more closely the form of the eyes coupled with the previous characters will distinguish it among the UK fauna.
4-6mm. Body entirely black with dense round, dull brown or bronze metallic scales and sparser small erect scales which are much longer towards the apex; base of elytral suture glabrous, appendages variously pale. Head with a curved transverse ridge from the posterior margins of the eyes and longitudinally impressed on the vertex, with very convex and asymmetrical eyes and a quadrate rostrum, scrobes terminating below the eyes. Antennae inserted near the rostral apex, scape gently curved and rather abruptly thickened before the apex, club long and pointed. Pronotum transverse rounded and without borders laterally, surface with deep and wide punctures and a central longitudinal impression. Elytra broadly oval with sloping shoulders and near-parallel lateral margins; striae strongly punctured, interstices each with a row of long semi-erect broad and truncate scales. Legs long and robust, with dense recumbent scales as well as small semi-erect scales; femora unarmed, inner margin of pro-tibiae curved inwards at the apex, and all tibiae lacking spurs at the inner apical angle. The dorsal surface colouration varies but there are usually two longitudinal bands of paler scales to the pronotum which extend to the elytral base, otherwise the elytra are usually randomly mottles with patches of pale scales on a darker ground colour.