Last Sunday I walked across the heath with my ex-next door neighbour, Matthew – he of the splendid garden at Troyes House that I visited back in the early spring. (See this post for a walk around it complete with some super vocal birds.)
As we passed the massive hollow-trunked oak tree near my path up to my new house that I wrote about back in May Matthew pointed out that among the proliferation of egg shaped acorns that now festooned its branches were a number that had sprouted tiny little ruffs from their pointy end. He said that they were oak galls.
As far as he could remember from an episode in David Attenborough’s 2010 Life in the Undergrowth there were a particular family of wasps who sought out acorns with a tiny blemish so that they could burrow inside and lay their eggs. Happy ensconced in their new home the larvae grow and multiply, feeding happily on the contents of the acorn. In due course, when they are ready to face they world they burst out of the acorn, scattering it to the four corners – and get on with their lives as wasps.
So, on the way back I stopped off to video the acrons and hopefully a wasp at work. Well, I got the video of the about-to-be blasted acorns – but the only wasp I could find seemed far more interested in grooming him/herself on a leaf than in laying eggs in an acorn. So sorry….
(If you want to see the videos you will need to click onto the blog as the email notification does not include the video.)
Anyhow, when I got home, I investigated a bit further – and the RHS were most helpful.
It appears that they are called oak gall wasps and that there are loads of different ones – around 70 in Britain alone. They have delightful names: Oak apple gall wasp, Oak marble gall wasp, Common (and smooth) spangle gall wasps, Silk button gall wasps, Oak cherry gall wasp, Knopper gall wasps….. They also seem to have rather complicated sex lives….
In general oak gall wasps alternate between generations that are either asexual (all females) or sexual (males and females). The generation that emerges as adults in summer has both sexes, whereas the generation that develops as adults in late winter-spring is all female.
They can also affect all different bits of the tree. Not just the acorns but the twigs, the underside of the leaves and the leaf margins. But wherever they make their homes, the oak trees seem totally relaxed about them so, as the RHS says:
As Oak gall wasps have little or no impact on the tree’s health and growth, control is not necessary nor is any available.
For a really amazing selection of pictures of the various different galls, see this post on the Woodland Trust site. This is their image of Lime Nail galls – courtesy of Roger Griffiths /Wikimedia.
My daily blog now has an Instagram account! WalksonHampsteadHeath – the idea being to widen the circle of people who might enjoy a daily ramble across the heath. Please follow us and pass on the news!! If you would like to get a notification of each new post, please ‘subscribe’ in the box on the right. It is very easy to ‘unsubscribe’ you if you get bored! You will get an email asking you to confirm your subscription but if it does not appear, check your junk box.