As I've wandered the trails around The Lodge recently, I've noticed something strange. Where there should be smooth, shiny, ripening acorns dangling from the oak twigs, there are distorted, crinkly growths which - to my eyes, anyway - look a bit like Ferrero Rocher chocolates...
It turns out that this is the work of a small wasp which goes by the snappy name of Andricus quercuscalicis. The weird growths themselves are known as 'knopper galls' - the word knopper being derived from a word for a knob, stud, tassel or hat.
The 'gall' is the growing acorn's response to the wasp grubs developing inside after eggs were laid there earlier in the year. In a similar way, you might have seen the robin's pincushion gall before - it's a common sight on wild rose bushes, with a tangled mass growing from the stem eventually turning red.
At The Lodge, at least, there are not many acorns to be found this autumn. The galls are turning brown and falling off the trees, and the newly-hatched wasps making their escape.
Jays are famous for their love of acorns, able to store away as many as 5,000 for a rainy (or cold) day. What will they do here this year?
As members of the crow family - clever, bold, adaptable and omnivorous - I doubt jays will go hungry. They just might need to look for some different foods in different places, so I wonder if that could mean an influx of jays to garden bird tables? In the same way, might we see squirrels launching a hunger-fuelled assault on our feeders?
Let us know what you see!
Have you spotted knopper galls on your local oak trees? Leave a comment and let me know.
Wow, that's a lot of comments!
The wasps which cause the acorn galls need the presence of a Turkey oak nearby to complete their life cycle, so presumably this problem will only be seen where those non-native trees are present. See: en.wikipedia.org/.../Andricus_quercuscalicis
I don't think there's anything which can be done to the affected trees, and perhaps the wasps have had a particularly successful year. Next year might be different!
As usual, grey squirrels have polarised opinion. If you want to discourage them from your garden, we've got plenty of suggestions: www.rspb.org.uk/.../greysquirrels.aspx or you could try asking for tips on the Community: www.rspb.org.uk/.../14005.aspx
Regarding squirrels' impact on bird populations, there's been quite a bit of research done, which you can read about here: www.rspb.org.uk/.../Predator%20Report_tcm9-177905.pdf
I've seen some oak trees chronically and extensively infected with this problem. However jays seem to be increasing both in numbers and boldness. One reason may be their adaptability re. food sources. They take very many fir cones in my local cemetery.
As for grey squirrels - persistent little beggars - I saw a cat kill one in the street near me.
The balance of nature is complex and ever evolving.
We live in a suburb of Birmingham with lots of mature oak trees, which we pass on our way to my daughters' school. Acorn numbers vary from year to year, but this year for the first time my 9-year old picked up something that she described as a 'disabled acorn', which I think might be one of your galls. They are small and brown, and we have found them scattered on the ground. There have been some acorns too, however not all that many as yet. Will try and collect some galls to photograph once it stops raining...
more for John Cooper re the Robin's pincushion gall - have a look at this: www.bugsandweeds.co.uk/galls%20p1.html
John - that's a Robin's pincushion gall
We spend 90% of net income on conservation, public education and advocacy
The RSPB is a member of BirdLife International. Find out more about the partnership
© The Royal Society for the Protection of Birds (RSPB) is a registered charity: England and Wales no. 207076, Scotland no. SC037654