Archarius Gistel, 1856
Of the 30 or so species of this widespread Palaearctic genus only six occur in Europe (although another species, A. ziliolii has recently been described from Italy (Diotti, L. & Caldera, R., 2013)), three of these are widespread but only two extend to the UK, the widespread A. crux (Fabricius, 1776) reaching southern Fennoscandia but not the UK. Together with Curculio Linnaeus, 1758, our two Archarius represent the UK species of the subtribe Curculionina Latreille, 1802, they are easily separated by the smaller size, <3.0mm, more-or-less uniformly black colour and the form of the antennal club; in the present genus the basal segment is as long as the rest of the club whereas in Curculio it is about the same length as the second segment. The only other UK species likely to be confused with Archarius is Anthonomus rubi (Herbst, 1795), with experience the more slender form of rubi becomes obvious but they are readily separated by the placement of the pro-coxae; in Archarius they are positioned near the rear margin of the prosternum whereas in Anthonomus they are equidistant between the anterior and posterior margins (obvious in side view).
Archarius salicivorus (Paykull, 1792)
This is among the most widespread members of the genus; it is locally common throughout Europe, reaching the northern Mediterranean but except for Algeria apparently absent from North Africa, extending north to the Arctic Circle in Sweden, and east through central and northern Russia to the Pacific coast. It has also recently been recorded from Canada (Quebec) and appears to be established there. Here it is generally common throughout England and Wales though more local in the north and very local and rare in the north of Ireland and Scotland north to Orkney. Adults feed on foliage and are active over a long season from April until October but may also be found during the winter when they remain in subterranean pupal cells. Habitats include wetland margins, and damp woodland and wooded parkland where the hosts, which include a range of willows, are present. Larvae develop within galls induced by wasps of the genus Pontania Costa, 1852 (Hymenoptera, Tenthredinidae), on the continent but the range of hosts in the UK is not known and other genera may be involved. Several larvae develop within each gall, feeding on the plant tissue (not predating other larvae as sometimes stated although the wasp larvae usually die through competition for suitable tissue) and exiting when mature to fall to the ground and pupate in a subterranean cell. Both the weevil and the host have two generations each year, the late brood of weevils coinciding with the late summer/autumn generation of galls.
This small weevil may be recognized by its long slender rostrum, elongate-oval body form and entirely black or dark grey colour. Males are on average a little smaller (1.8-2.5mm) than females (2.0-2.8mm), have a shorter rostrum and a stronger tooth to the tibial apices. Dorsal surface with moderately dense fine pale grey scales, ventral surface with dense pale scales which obscure the cuticle on the prosternum and mesosternum and laterally on the metasternum. Head from above transverse with convex eyes that occupy the entire margin, the inter-ocular distance slightly shorter than the width of the rostrum across the base, antennae entirely dark; funiculus 7-segmented. Pronotum broadest in front of rounded posterior angles and narrowed to a subapical constriction before a straight anterior margin, surface strongly and densely punctured. Scutellum with dense white scales. Elytra broadest at rounded shoulders and gradually narrowed to a continuously curved apical margin, striae deep and strongly punctured, interstices wide and flat, each with 2-3 rows of narrow pale scales. Middle and hind femora with a distinct ventral tooth, fore tibiae broadened apically, middle and hind tibiae with a strong apical spur which is more developed in the male. Claws in both sexes with a sharp tooth near the base.
Archarius pyrrhoceras (Marsham, 1802)
A locally common species from lowlands to 700m throughout most of Europe, extending north into Fennoscandia and occurring widely across Mediterranean North Africa, the Asian distribution is much more restricted than the previous species, extending through Russia and Ukraine as far as western Siberia. Here it is common across Wales and England north to the Humber but much more local and rare further north and there are only a few scattered records from Scotland and the north of Ireland. Host plants include various native oaks, especially common oak (Quercus robur L.) and sessile oak (Q. petraea (Matt.)) and the weevils may occur wherever these are common, woodland and wooded parkland etc, but also on isolated trees in hedgerows and gardens. Other species may also host the beetles as on the continent they have been recorded from downy oak (Q. pubescens Willd.), Oriental hornbeam (Carpinus orientalis Mill.) and dogwood (Cornus mas L.). Adults are active from March until October when they may be beaten from low foliage and they overwinter in the soil close to host trees. Adults feed on leaf buds and foliage, mating occurs during May and Females oviposit into galls produced by the wasp Cynips quercusfolii Linnaeus, 1758 (Hymenoptera, Cynipidae) and possibly other species, and consume the modified parenchyma within the gall. Several larvae usually occupy each gall and when fully-grown they bore out of the galls during the summer, drop to the ground and pupate in a subterranean cell. The resulting adults may remain in the cell or become active before the winter, little is known of their biology, but the species is believed to be univoltine.
Similar in size and habitus to the previous species but distinct in having the antennae and, in the male, the pro-rostrum, substantially red. Males are slightly smaller (1.6-2.2mm) than females (1.6-2.4mm) have a shorter and less strongly curved rostrum and larger tibial spurs. Dorsal surface with moderately dense pale seta-like scales, ventral surface densely scaled, especially towards the margins. Head transverse with convex eyes that occupy most of the margin, the temples usually retracted into the prothorax, surface strongly punctured and usually with more dense scaling between the eyes. Pronotum rounded laterally in the basal half and narrowed to an almost straight apical margin, posterior angles rounded and basal margin sinuate, surface strongly and diffusely punctured, the fine scales oriented obliquely or transversely. Scutellum with dense white scales. Elytra broadest at rounded and slightly protruding shoulders and evenly narrowed to a continuous apical margin, striae narrow, deep and punctured, interstices flat and each with one or two rows of setae-like scales. Middle and hind femora without, or with only a very rudimentary ventral tooth, fore tibia expanded towards the apex, middle and hind tibiae with a strong apical spur which is larger in the male. Claws in both sexes with a sharp internal tooth near the base.