Green Weevils

Polydrusus Germar, 1817

Polydrusus is a Holarctic genus of about 200 species in 19 subgenera, the greatest diversity is in the western Palaearctic region and about 112 species of 18 subgenera occur in Europe, mostly in warmer southern regions, while 7 species are recorded from the United States and of these 4 extend north into Canada. They are generally absent further south but several extend into North Africa and the oriental region and a few are known from Central America, Mexico and the West Indies. Superficially similar to Phyllobius and Pachyrhinus but readily separated by the form of the scrobes, they are generally more elongate and slender and the genus includes more arboreal species, some of which are occasionally serious pests of fruit and nut trees, most are clothed in round scales which may be brown, grey, green or yellow and many are patterned or metallic, most have at least partially pale legs and antennae and the femora may be toothed or smooth. Unlike our Phyllobius species, all have the claws fused at the base. Most follow a typical lifestyle with adults occurring between March and September, adults may eclose in the autumn and remain dormant in the soil until the following spring or larvae may overwinter in the soil, complete their development in the spring and pupate in the soil to produce adults in the spring, either way mating occurs in the spring and larvae develop through the summer. Adults are generally polyphagous or oligophagous on broadleaf trees and shrubs but herbaceous plants are also attacked, and larvae develop in the soil, feeding externally on roots. Most are fully winged and can fly and while most are bisexual the genus also includes some parthenogenetic species.

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• Polydrusus marginatus Stephens, 1831 is a small wingless species associated with flightless species associated with a variety of trees and shrubs although often found in pitfall traps or among moss and litter at the base of trees, it is generally rare and restricted to a few areas in the south of England. The species can hardly be described as a green weevil, most specimens being grey or slightly metallic coppery, but viewed in bright sun at least some have a greenish tinge and so might be taken for a true green weevil. Distinguished by the rather narrow body and lack of prominent elytral shoulders, the antennae are more robust than in other members of the genus and have the distal funicular segments quadrate or slightly transverse.

• P. mollis (Strøm, 1768) is a large (6.5-8.0 mm) and broadly-oval species with a narrow forebody and sloping elytral shoulders, it is generally metallic grey or coppery but distinctly greenish forms are not uncommon. The antennae are shorter than in most members of the genus and the femora are not toothed, the front and middle tibiae, and often the hind tibiae, have sharp external margins and the dorsal surface of the body is covered with hair-like scales. The species is locally common across England and Wales and adults occur on various trees and shrubs from April until August.

• P. formosus (Mayer, 1779) was formerly a rare species in the UK but has spread over recent decades and is now locally common on a range of trees and shrubs throughout southern and central England and Wales. The shape of the head, broadest across the base and tapering to large and rather weakly convex eyes, will distinguish this species. The antennae are long and slender, pale with a dark club, the femora have a small ventral tooth and the tibiae are not sharp externally.

• P. cervinus (Linnaeus, 1758) and P. pilosus Gredler, 1866 are dark species with a mottled appearance composed of patches of silvery or golden scales, some specimens have a distinct greenish hue but the mottled appearance is always obvious and will distinguish them from our true green weevils. P. cervinus is widespread and common throughout England and Wales while P. pilosus is a very local and generally rare species of northern England and Wales, Scotland and Ireland. Both occur on a range of trees and shrubs.

• P. pulchellus Stephens, 1831 occurs on a range of herbaceous plants in salt marshes around the coasts of England and Wales. Most specimens are  extensively greyish-green and many have contrasting longitudinal stripes of paler scales to the elytra but this varies and sometimes the greenish scales are only obvious around the margins, in any case the species may be recognized by partly or completely pale femora, broad pronotum and relatively narrow elytral base.

• P. confluens Stephens, 1831 is widespread but local across much of England and Wales, it occurs on broom and gorse, mostly on heathland or near the coast, and may be abundant where it occurs. The colour varies from grey to coppery or even silvery, and in this sense it is not a green weevil but specimens often resemble P. pulchellus, often having paler strips of scales to the elytra. P. confluens may be recognized by the entirely dark femora but the habitat will be a good clue as to which species is present.

• P. pterygomalis Boheman, 1840 is among the easiest of our green weevils to recognize due to a large swelling behind each eye. It is also among the most widespread and common of our green weevils, adults occur over a long season on various deciduous trees and shrubs.

• P. flavipes (De Geer, 1775) is a widespread though very local and generally scarce species of England and Wales, it occurs on a range of deciduous trees and shrubs though rarely in large numbers and often only single specimens or pairs are found. Very similar to the next species but the head is slightly convex and lacks a median impression.

• P. impressifrons Gyllenhal, 1834 was only recently (2012) discovered in the UK but it has become established and is spreading across the south of England, it occurs on a variety of trees but may be under-recorded because of similarities with the previous species. Here, as the name suggests, the head is impressed between the eyes but this is sometimes only slight and specimens may need to be examined carefully, and the vertex is slightly more convex when compared to flavipes.