Updated: Dec 8, 2020
If you happen to knock some trees about you will eventually find one of these guys…
Curculio glandium source: Udo Schmidt
These are the Curculio weevils, often referred to as the ‘acorn weevils’.
Admittedly you will only find 3 of the 6 UK species on Oak but for the sake of brevity lets leave that discussion for another day.
As a beginner I found it really difficult to split even the most common species, and now being less of a beginner I though I’d impart my experience.
One thing that's really good to know is when taking size measurements on weevils you ALWAYS MEASURE FROM THE FRONT OF THE EYES and ignore the long snouts (rostrum), the reason for this is that rostrum size varies greatly between sexes in some species.
Coleopterists like to keep this nugget of knowledge squirrelled away and it caused me confusion for months!
When finding these, the first thing you should do is note the food plant, this is good practice anyway for weevils as a whole, and it can save you a lot of hassle later on.
Heres a list of the UK Curculio sp. And their retrospective foodplants. Oak: C.venosus, C.gladium, villosus Hazel: C.nucum Birch: C.betulae, C.rubidus Willow: C.rubidus
Obviously these things fly all over the place and they will end up on really random plants occasionally, so use food plants as a guide rather than dogma especially in a densely packed woodland.
This is the tiny bit in the top center of the wing cases. All of the UK species have ‘roughly square’ (long as wide ) scutellum-like those pictured below (Coleopterists call this quadrate), except one… Curculio venosus, which has a scutellum that is oblong and is longer than it is wide (bottom image)
The elongate scutellum of C.venosus source:N.sloth
should be on Oak and 5.9-7.9mm long. I rarely find these, but they are apparently fairly frequent, so an uncommon species in my book.
Ok so its not venosus? lets carry on!
Ok look at the front legs of your weevil, and see if it has a small tooth on its femur.
The toothed Femur of Curculio glandium Source: Udo Schmidt
Species with a small tooth (go to group A):
C.glandium, C.nucum, C.villosus
Species that lack a small tooth on the front femur (go to Group B):
C.betulae, C.rubidus (Both of these species are Rare)
Group A: Weevils WITH a small tooth
Ok this is a bit tricky, especially if your weevil is alive and kicking , so if you are adverse to collecting specimens nab a decent shot of those antennal clubs!
You then need to decide which type of antennal club your weevil has.
Remember, its the last 4 antennal club sections you’re looking at!
Antenna A: More ‘squat looking’ (about twice as long as wide) and looks more bottom heavy?
It will be either:
Curculio nucum These should be on hazel and more than 6mm (size range 6.0-8.0mm) These do have a row of longer raised scales on the bottom 3rd (elytral apex) of the elytra where the two wing cases meet, this gives them a cool little mohawk if they are not too worn. Uncommon but local.
Curculio nucum showing the mohawk. Photo via Ben Sale
Curculio villosus These should be on oak and less than 5mm (size range 3.8-5.0mm) These lack the obvious elytral mohawk on their bum. They appear much darker than the other UK Curculio species almost appearing black, and on a fresh looking specimen have 6 distinctive patches of pale scales towards the apex of their elytra. A fairly uncommon weevil, listed as Scarce
Curculio villosus: swept from long grass under oak on a particularly windy day
Antenna B: Antennal club evenly tapered, elongate (about 3 times as long as wide)
Curculio glandium This should be on Oak and between 4.1-6.7mm. Its worth noting this is by far the most common Curculio species I see on my day to day beetle wrangling.
Curculio glandium source: Udo Schmidt
Group B. Species without a tooth on the front femur
Curculio betulae Has a small tooth on the middle femur and an obvious tooth on the hind femur. Found on either Birch and Alder and between 3.3-4.3 mm RARE
Curculio rubidus All femurs are completely unarmed and lack any form of tooth. This species can be found on both birches and willows and has a size range of 3.1-3.8mm RARE
I’d recommend using a decent and reliable webpage to compare images to double check the ID of your weevil against, like Kerbeiter’s European gallery, or our Coleoptera.org.uk. Edit: for this genus I’d recommend Coleoptera.org.uk which has 4 of the 6 Uk species listed.
If you are truly serious about getting into beetles, definitely worth picking up a copy of
Duff (volume 4 for all British weevils), its definitely not for the faint hearted but its the mother load of weevil info.
For any other Weevil enquiries its definitely worth looking at