Knopper Galls

Knopper galls are new to me, but there is an oak tree near our house which has lots of them.   They are caused by a gall wasp, Andricus quercuscalicilis, which lays an egg in developing acorns.   In turn this leads to a chemical reaction with the result that the acorn becomes grossly misshapen and host to the insect grub.

The wasp is an alien, and was first recognised in the UK in the late 1950's and early 1960's.   Judging from NBN data it now seems to be present throughout most of the UK, though remains commonest in the south and east.

I had a brief foray into the literature and there is some interesting work from the 1990's by Mick Crawley and others about the ecology of the wasp see eg. Hails and Crawley, where they were seeing as many as 60% of the acorns were affected.  Our tree, a native English, pedunculate oak,  had approximately a third of its acorns affected by galls.   The gall wasp does not damage the tree, just reduces the number of fruits.

At this time of year the grubs are just developing in what looks like an oval egg-case inside the disfigured acorn.  Often other parasites are found in the gall but I found only the gall wasp in the two galls I cut open (and getting a very sticky mess in the process).

The really interesting thing though is that the wasp needs not one but two host species.  It has two generations, one asexual the other sexual, each dependent on a different tree.   In addition to the native oak where the asexual wasp lays its eggs, there is a second generation where the emerged insect mates and eggs are laid in the buds and catkins of the introduced Turkey oak.  

I therefore spent an hour this afternoon looking for Turkey oaks around the village.   The nearest I found was a big old tree at the school, next to a younger native oak, whose acorns were affected.   The distance between the Turkey oak and our oak is 320 metres if the gall was flies in a straight line and does not get diverted.  How does the gall wasp find the host?

Early Days - a New House

We have moved within the village from a 17th century cottage, to a new house on an estate at the edge of the village.  The house move was not that stressful compared to the challenge of getting internet access.  It took 6 weeks to get broadband, due to the obduracy of Openreach, and we gave up contact with the world whilst we waited.   At one point we were told that no broadband service was possible because the nearest telephone cabinet was over 4km away rather than the 300 metres it actually is. We have now thankfully travelled forward from the 20th century to the 21st.

The estate is built on what was a pasture, and we face the original hedge which was the field boundary.  Needless to say that the development was controversial because of its siting, and there is still a lot of opposition even though it is now built.  It should all settle down in around 10 years or so, judging from another controversial development back in the 90's.

The hedge is a mature with hazel, blackthorn, field maple, crab apples, ash and pedunculate oak.   Behind lies a playing field and beyond that open countryside.   So far we have had a fox stroll by, and a muntjac exploring the hedge. as a scratchy video from my mobile demonstrates  https://youtu.be/Nx2mzNUMGIU.   3 families of mallard ducklings were raised on a nearby pond, and a piece of land which regularly floods and had standing water until the end of July had a Little Egret.

Within a couple of days of moving my wife put up three bird feeders - peanuts, grain and niger seed. (We are now back to dispensing industrial quantities of bird feed).   Blue and great tits were the first to appear on the feeders followed by dunnock and robins.   Goldfinch arrived only after a few weeks but they are now regulars.   From time to time we get clouds of housemartins circling around, occasionally perching on the roof.

A few butterflies so far including Speckled Wood, Large White, Small Tortoiseshell, and a Painted Lady.   This Southern Hawker Dragonfly has been a regular.

Early days!