Phyllobius pomaceus Gyllenhal |
Green Nettle Weevil
Order: Coleoptera – beetles
British distribution: Widespread, locally common.
World distribution: Northern and western Europe, extending into northern Asia.
Phyllobius pomaceus (= P. urticae De Geer) is a weevil, i.e. a beetle of the family Curculionidae, in which the head is extended into an elongated snout, the rostrum. It is a frequent and sometimes conspicuous species on patches of Stinging Nettle (Urtica dioica) and is the commonest green-coloured weevil on this plant. Although often called the "Nettle Weevil" or the "Green Nettle Weevil", there is confusion over these names (see below).
|Phyllobius pomaceus on Urtica dioica, Weardale, Co. Durham, June 2006.|
Light souce: natural daylight (blue sky), causing the beetle to reflect this colour.
Phyllobius is a genus of "short-nosed weevils", in which the rostrum is relatively short and extends little beyond the points of attachment of the antennae.
P. pomaceus is a well-known species but requires attention to critical characters for certain identification. It is by no means the only green weevil of metallic appearance and even on nettles it is readily confused with other species. Numerous images are posted on the Web, but not all are correctly named. Misidentified images include those claiming the species on host plants other than Urtica.
Although described here as "green", it should be noted that the basic colour in this species is black, but with the beetle extensively coated with metallic, typically green to blue-green (sometimes also golden or coppery) scales. With age, more of the black ground colour is revealed as the scales are rubbed off. Perceived colour may also depend on lighting; photographs shown here were taken in natural daylight under a blue sky and it seems that the beetle appears more strongly green under artificial light or with flash.
Ten British species of Phyllobius are listed by Morris (2008). A useful account of most of these species, with coloured illustrations, was provided by Linssen (1959). The genus is characterised by a scaly pubescence or by the tiny, metallic scales, which in most species coat the entire dorsal surface of the insect. The colour of these scales varies in many species, including P. pomaceus, from various shades of green to coppery brown. The majority are leaf-eaters, non-specifically on various trees.
The genus Polydrusus is very similar, the distinction being that the "scrobes" (the furrows in the rostrum into which the first joints of the antennae fit) are curved rather than straight – diagram in Joy (1932).
In continental Europe, Chlorophanus is another, similar genus. C. viridis, illustrated in Harde (1984), resembles P. pomaceus very closely but lacks femoral teeth (see below), has shorter antennae and occurs on alders (Alnus) (Harde, op. cit.).
Vital characters for confirmation of P. pomaceus are:
i) relatively large size, length 7-9 mm;
ii) the femora each bear a conspicuous, more or less ventral tooth (most easily seen on the front pair of legs);
iii) the legs are black beneath the scales;
iv) the antennae are dark beneath the scales, though tinged rust right at the base and sometimes at the tips;
v) nettles (Urtica) as the host plant.
|Two closely related species, also green and also occurring or reported on nettles are:|
|• ||P. virideaeris (Laicharting)|| |
length to 4.5 mm; femora with swellings but lacking distinct teeth; ground colour of antennae and legs red to rust-coloured, or femora darker; underside of abdomen thickly covered with scales; elytra in side view evenly rounded from dorsal region down to the posterior; polyphagous on various trees and other plants – the supposed association with nettles may be due to former use of the name for the following species. Various sources also dub this the "Green Nettle Weevil", but confusion with P. pomaceus, either in name or identification, seems likely – it is NOT the common and conspicuous green weevil characteristic of nettles!
|• ||P. roboretanus Gredler|
(= P. parvulus Olivier)
very similar to P. virideaeris but length to 3.5 mm; underside of abdomen with no more than sparse pubescence; elytra in side view ± abruptly curved down to the posterior. Dubbed the "Small Green Nettle Weevil" and noted as occurring on nettles by Linssen (1959), but not listed as especially associated with nettles by either Philp (1991) or Bullock (1992) and presumably polyphagous.
Characters are taken from Linssen (op. cit.) and Joy (1932). Linssen also mentions P. pyri, another polyphagous species, as often occurring on nettles. Typically it has coppery scales but it can be greenish and it has femoral teeth. However, its legs are yellow and its antennae are rust-coloured or red.
P. pomaceus feeds openly on the leaves of Stinging Nettle (Urtica dioica) and is host-specific (Philp, 1991). Individuals are often numerous and so relatively conspicuous on nettle colonies in early summer. The larvae are root feeders, presumably on the same host. It should be noted that the epithet "pomaceus" evidently refers to the (sometimes) apple-green colour of the beetle (literally resembling an apple), and does not indicate any feeding relationship with apple trees.
Morris (1991) wrote a very useful introductory guide to weevils, primarily to British species, with notes on their ecology and biology. It includes a short section on weevils of nettles that includes P. pomaceus but not other Phyllobius species.
|• ||Bullock, J.A., (1992). Host plants of British beetles: a list of recorded associations, Amateur Entomologists' Society, Feltham.|
|• ||Harde, K.W., (1984). A field guide in colour to beetles, Octopus Books, London.|
|• ||Morris, M.G., (1991). Weevils. Naturalists' Handbooks 16, Richmond Publishing Co., Slough.|
|• ||Morris, M.G., (2008). Family Curculionidae, in Duff, A.G. (ed.), Checklist of beetles of the British Isles, 2008 edition, http://www.coleopterist.org.uk/checklist2008%20A5.pdf.|
|• ||Joy, N.H., (1932). A practical handbook of British beetles, 2 vols., H., F.& G. Witherby, London.|
|• ||Linssen, E.F., (1959). Beetles of the British Isles, series 2, F.Warne, London.|
|• ||Philp, E.G, (1991). Vascular plants and the beetles associated with them, in Cooter, J., (ed.), A coleopterist's handbook, ed. 3, Amateur Entomologists' Society, Feltham, pp. 183-198.|