This is a species I have never seen though the distinctive holes it leaves in hazelnuts were a familiar sight in my childhood in Gwent when gathering nuts in the autumn. I know other coleopterists have encountered this species rarely or not at all and there is a general belief that it has declined severely. Presumably Grey Squirrels are to blame as they have increased in recent decades and most hazelnuts are now eaten by squirrels before they’ve ripened.
Has it declined? Was it ever common? Fowler (1891) referred to it as “local; generally distributed in the London district and the South of England …”, and Joy (1932) gave it as local. Roger Booth investigated this in 2003 by surveying some of the early beetle collections at the Natural History Museum. It is not always easy to interpret such sources but, for example, C.E. Tottenham recorded adults on 9 occasions in a 38-year period (1911 – 1949) totalling only 10 specimens. Roger concluded that the weevil never was very abundant.
Nevertheless, it does look as though C. nucum is rarer now. It now seems to be a species that an active coleopterist will encounter about once in every 20 years (or less often than that in my case!).
So, I was really pleased to see lots of hazelnuts with holes in on the Isle of Wight on Monday (12th September). I picked up 141 hazelnuts of which 14 had C. nucum exit holes. The island is still free of Grey Squirrels and maybe the local Red Squirrels are less voracious in their appetite for hazelnuts?
We could get a much better idea of the current status of C. nucum by recording exit-holes in hazelnuts rather than looking for the adults on hazel bushes in May and June. I’m going to start keeping more of an eye out and I’d be interested to hear what others find.
The hole is made by the fully-grown larva as it exits the nut before overwintering in the ground where it will pupate in the following spring. I’ve brought some nuts home from the Isle of Wight in the slender hope that there may be some larvae still to emerge, and in the even more slender hope that I’ll be able to rear them through to adulthood in 2012.