Galls
Galls
I well remember the first time I saw an oak apple. I was about six, and we were on an expedition up through the fields to the Bleach Mill dam at Burley Woodhead, now drained and overgrown but once the best place in our area for tadpoles and frogspawn. Our path wound along beside a beck, with deep pools in which to spot small brown trout and shallows invaded by clumps of monkey flower and water mint. On its bank grew an oak, long ago felled to a stump but with a few branches still sprouting, and on one of its branches this hard brown sphere about the size of a boiled sweet – an oak apple. I learnt the name but it was many years before I understood its origin.
Oak apples are galls, and this is a specially interesting one. A particular species of wasp lays its eggs into the base of a leaf bud in spring, the larvae hatch and as they begin to feed inject a chemical substance that causes the plant to develop a protective substance around them – the ‘apple’ – in which they can grow and change. In summer male and female wasps emerge and mate. The female lays eggs in the soil on the root of the tree forming a similar gall there. From this, wingless females emerge, climb the tree and lay eggs and so the cycle of Alternative Generation continues.
The other gall familiar from childhood is the robin’s pincushion, that posy-like arrangement of pinkish-gold bristles found on wild rose bushes. This, too, is the work of a tiny wasp that lays her eggs into the leaf bud. The feeding larvae induce the plant to form protective cells from which the adult insects emerge. These are mainly female and produce the next generation of eggs without benefit of males – an intriguing process called Parthenogenesis.
These childhood memories have been stirred up because a friend told me about a much rarer gall recently discovered on bracken in Grass Wood. It’s the work of a little-researched species of midge. Each gall looks rather like a small black sausage, though examination through a lens reveals a dark red tinge. Our inventive ancestors gave it the name – little black pudding. It’s a new record for Grass Wood, and a reminder of how complex and endlessly surprising the world of our insect neighbours is. How very resourceful to be able to induce a plant to house and feed you without causing the host any damage.
Of course, not all galls are caused by insects. One of the most spectacular – the witches’ broom – that tangle of twigs, looking like an untidy crow’s nest, in the branches of birch trees – is the result of a fungus. And that reminds me – we are entering the best time of year to look out for those more familiar fungus forms, mushrooms and toadstools. Apparently it’s a great year for field mushrooms. A friend living near Malham tells me he could have collected ‘a wheelbarrow load’ of them on his morning dog walk. That reminded me of my father’s stories of school holidays spent with cousins in Hawes when they went mushrooming with a clothesbasket.
