Compare the two Glocianus weevils in these images (click for large images). I didn’t think they could be the same species …
… and I thought my Sutton Bingham Reservoir specimen had to be something new to Britain. But they are both specimens of Glocianus punctiger. That is the opinion of Italian weevil expert Enzo Colonnelli, and there is nobody with greater experience of these species across Europe.
I haven’t found Glocianus weevils very often, though more so in recent years as I’ve started to use my suction sampler more and more routinely. To date I have recorded Glocianus distinctus on 5 occasions (6 individuals), G. punctiger on 4 occasions (4 individuals) and have not yet found the other two British species: G. moelleri and G. pilosellus. I’ve been keying them out using Mike Morris’ RES Handbook (Morris, 2008) but also dissecting males as a matter of routine. The two males pictured here are the only two males of G. punctiger that I have found. I thought I’d been lucky and discovered a species new to Britain but actually I’d been unlucky and found a specimen with really unusual genitalia! Anyway, it seems worthwhile to bring this to other peoples’ attention, especially as this is an extreme degree of variation to find within one species. I will certainly be dissecting and retaining any other male punctiger I find, to learn more about the variability of aedeagal structure in British populations. And as Enzo has said: “variation is the engine of evolution”!
Glocianus punctiger feeds on dandelions Taraxacum, mainly the Section Ruderalia which is by far the commonest Section of this large genus, and mostly includes micro-species which are weeds of lowland areas. Although the host plants are widespread and abundant, the weevil is much more restricted, typically being found in grasslands, waste places, at the sides of roads and tracks, in woods and in open and rough ground generally (Morris, 2008). It occurs very locally throughout England and Wales and has Nationally Scarce (Nb) conservation status.
I am very grateful to Mike Morris for all his help in investigating the identity of the Sutton Bingham specimen and for putting me in touch with Enzo Colonnelli, to whom I am very grateful for letting me have his opinions on my photographs. As ever, I am indebted to James Hogan, Zoe Simmons and Darren Mann at the Hope Department of Entomology, Oxford University Museum of Natural History, for access to their digital auto-montage equipment. The atypical specimen from Sutton Bingham Reservoir was found during surveys of the invertebrates of unimproved grassland habitats for Wessex Water.
Morris, M.G. (2008). True weevils (part II) (Coleoptera: Curculionidae, Ceutorhynchinae). Handbooks for the identification of British insects, vol. 5, part 17c. St Albans: Royal Entomological Society.