Otiorhynchus tenebricosus (Herbst, 1784)
More generally known as O. clavipes (Bonsdorff, 1785), this is a very local and generally scarce species throughout central and southern Europe from France to Ukraine and western Russia and north to the UK and Denmark, throughout much of this range it is more prolific in deciduous and mixed mountain forest areas but it now occurs more generally as it is widely polyphagous and the subterranean larvae are readily transported with horticultural products. Here it is very local across south and central England and generally rare further north, across Wales and in Northern Ireland, it was formerly present as far north as Southern Scotland but it seems to have declined over recent decades. Typical habitats are mostly in dry chalky districts, often in upland areas on grassland or at the roots of various trees and shrubs and it is also an occasional pest of cultivated fruits. Adults appear from late April or May and again from mid-June until August, their appearance depending upon when pupation occurred; they overwinter either as young larvae which will develop through the spring and pupate in early summer, or as fully-grown larvae which will pupate early in the spring, pupae have also been known to overwinter and produce adults earlier in the year. They are nocturnal, feeding on the foliage of a wide range of herbaceous and woody plants by night and hiding under stones or among foliage by day, reproduction is both parthenogenetic as well as sexual, mating occurs after a period of feeding and pairs may be found over a long season from May or June. Females are fecund and each may produce up to 300 eggs which they scatter in batches onto the ground beneath likely host plants, larvae emerge after about 3 weeks and enter the ground to feed on plant roots, they pass through three instars and develop rapidly although even those from early summer, except for the few that pupate late in the year, will go on to overwinter. As a pest they rarely cause serious damage, adults feed on developing foliage and fruit buds and later in the season they may attack the stems of raspberry canes etc, the damage is usually slight but where the species becomes established the larvae may cause more serious damage by attacking the roots of soft fruits. Adults may be sampled by sweeping grass and low foliage around trees and shrubs at night; on the continent, and especially at higher altitudes, they are often more prolific in woodland where the adults feed on developing shoots of both conifers and broadleaf trees and larvae develop among the roots, but more generally the species feeds on a very wide range of plants; when we found them in the Chilterns they were just as numerous on hazel and hawthorne (etc) in hedgerows and copses as they were among long dry grass on open hillsides and so sweeping any vegetation on chalky soil at night is probably worthwhile. Adults can be seen by torchlight on foliage and they also sit on fence posts etc for long periods but they drop to the ground at the slightest disturbance and can be very difficult to find.
Otiorhynchus tenebricosus 1
Otiorhynchus tenebricosus 2
Adults vary in size and general appearance to the extent that in the field it is easy to imagine several species in the sweep net, the elytral sculpture and pubescence and the relative proportions of the body parts and appendages vary and several forms or subspecies have been named, on the continent where the situation is much more difficult because of the large number of species it is thought that the various forms constitute a species complex but UK specimens are all included in the present species. 8.5-12.5mm. Long-oval with characteristic tapering pronotum and elytra, body shiny black and smooth or weakly granulate, legs variable but usually at least to some extent red, antennae black. Head flattened and finely punctured between weakly convex eyes, rostrum elongate and expanded in the apical half where the scrobes are visible from above, the surface very variable from flat to longitudinally depressed or ridged, antennae long and slender; the seventh and eighth segments elongate and the club at least four times longer than wide. Pronotum broadest at or a little behind the middle and narrowed to slightly obtuse posterior angles and rounded (from above) anterior angles, the surface evenly convex, finely and densely punctured across the disc and weakly granulate or folded towards the lateral margins. Elytra broadest in the basal half and smoothly curved from sloping shoulders to a narrowly-rounded apical margin, finely punctured and with a variable mesh-like microsculpture throughout, striae variably impressed and punctured, sometimes almost absent in females, interstices flat to weakly convex and variably rugose, in most specimens there are at least some scattered scales or small groups of scales. Legs entirely black to entirely red but usually red with the apex of the femora and base of the tibiae darkened. Femora clavate and smooth ventrally, front tibiae expanded to a curved internal tooth at the apex, the outer margin smoothly rounded, middle and hind tibiae expanded both internally and externally at the apex. Females are generally broader than males, the front tibiae are less strongly curved towards the apex and the elytra are less strongly sculptured.