Acorn Weevil Curculio glandium

This is one of the beetles I see most often, especially at light, but it's also one that has given me considerable problems with identification. I haven't always found separation from Curculio venosus straightforward, but the real problem for me has been separation from Nut Weevil Curculio nucum. I have previously identified a few of the latter but I have no specimens that I still believe to be that species and I'm no longer confident about any of my previous records of that species.

Both Duff and Hackston major on the shape of the antennal club, stating that this is about twice as long as wide in nucum and about three times as long as wide in glandium. I suspect this rather exaggerates the difference as the vast majority of examples I have examined, at least those I've measured, have been between two and three times as long as wide, and not particularly near either end. Typically they (and they've probably all been glandium) have been around 2.7x as long as wide, with a few being nearer 2.6x. While this is clearly nearer 3x than 2x, it's far enough away from 3x that I wouldn't describe it as "about 3x".

Various references refer to the hair scales or bristles on the other antennal segments and Paul Brock's "A Comprehensive Guide to Insects of Britain and Ireland" illustrates this with photos of both species' antennae. Unfortunately this completely misrepresents the difference as I believe it shows a female glandium and a male nucum, and as I've been reviewing my old records and specimens trying to make sense of this character I've come to the conlusion that the difference between males and females is greater than the difference between species. Indeed, Mark Gurney's guide (which it didn't occur to me to look at until I'd nearly finished my review) makes this very point. Brock's photos heavily influenced my previous identifications of nucum - in some cases my notes reveal that the proportions of the club left me in doubt but after comparing the funiculus segments with Brock's photos I felt they had to be nucum - but in reality they were simply male glandium (or in a few cases where the large size contributed to my identification, I may have overlooked venosus). Perhaps there was the odd nucum among them - there is a large Hazel tree overhanging my garden after all - but I now suspect that I haven't yet found a true nucum.

There is much overlap in size between glandium and its congeners but size was helpful when I was trying to get to grips with them as although some are larger or smaller, those falling between 5.1mm and 5.8mm are outside of the quoted ranges for any of the other Curculio species. A significant proportion of what I eventually felt happy were glandium were between 5.1mm and 5.8mm long which is too small for nucum (or venosus) and too large for villosus (and betulae and rubidus which are more straightforwardly eliminated by their unarmed fore femora). I never place too much importance on size, but the fact that so many of them were in this range certainly helped give me confidence that I was now getting them right.

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 5th September 2025

Neither Duff nor Hackston resort to comparing the genitalia of Curculio but when I'd almost finished reviewing my records it occurred to me that the Beetles of Europe website (coleonet.de) might have some genitalia photos and that might help. Sure enough it does show male genitalia for glandium and nucum, though not venosus and several other species. I'd already concluded that this one was a male glandium, but as I hadn't yet disposed of the specimen I thought it would be a good one to check. The apex is bent right over so difficult to observe and photograph at the right angle to see the shape well, but I think it confirms my identification - at least it certainly rules out nucum.

Acorn Weevil Curculio glandium showing scutellum, apex of elytra, antennal club, antenna, foreleg and aedagus (six views), North Elmham (Norfolk, UK), 28th August 2024

Acorn Weevil Curculio glandium showing scutellum, apex of elytra, fore femur (2 photos), antennal clubs (both) and antenna, North Elmham (Norfolk, UK), 13th August 2024

Acorn Weevil Curculio glandium showing scutellum and antennal clubs, Wendling Beck Environment Project (Norfolk, UK), 13th April 2024

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 15th August 2018

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 14th August 2018

When I looked at the antennal club on this my first thought was that the proportions suggested nucum rather than glandium, but there was something odd about it. On closer inspection, the club was not formed of four segments and then I noticed that there was no funiculus at all! It was the same on both sides and showed no sign of a break, so presumably this one's antennae were malformed during development. Of course that made it hard to confirm, but it was caught with two other glandium and I could see nothing to suggest it wasn't the same.

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 6th September 2025

second Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 6th September 2025

third Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 6th September 2025

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 16th August 2017

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 16th September 2018

second and third Acorn Weevils Curculio glandium, North Elmham (Norfolk, UK), 16th September 2018

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 18th August 2018

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 2nd September 2024

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 21st August 2019

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 22nd August 2024

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 3rd August 2022

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 3rd September 2024

second Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 3rd September 2024

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 31st August 2024

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 12th August 2018

second Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 12th August 2018

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 15th May 2020

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 17th May 2020

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 19th May 2018

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 27th May 2020

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 3rd August 2020

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 3rd September 2019

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 4th August 2019

Acorn Weevil Curculio glandium, North Elmham Cathedral Meadows (Norfolk, UK), 7th August 2019

Acorn Weevil Curculio glandium, Wendling Beck Environment Project (Norfolk, UK), 26th April 2022

Acorn Weevil Curculio glandium, East Wretham Heath (Norfolk, UK), 20th June 2015

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 1st August 2020

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 12th August 2020

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 14th August 2020

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 15th August 2020

4x Acorn Weevils Curculio glandium, North Elmham (Norfolk, UK), 19th August 2020

4x Acorn Weevils Curculio glandium, North Elmham (Norfolk, UK), 20th August 2020

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 21st August 2020

second Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 21st August 2020

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 5th August 2018

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 8th August 2020

Acorn Weevil Curculio glandium, Syderstone Commmon (Norfolk, UK), 6th August 2016

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 27th August 2014

Acorn Weevil Curculio glandium, North Elmham (Norfolk, UK), 29th August 2014