Out to the 'new' Histon wood this morning, on a day of flat light, white sky, and almost no breeze. I was looking for some green shoots of Spring, but they were conspicuous in their absence. Everything seemed dead or dormant, so I turned my attention to signs of past life on the oak trees in the wood.
The variation between the oak trees is amazing. They were all planted at the same time, all as 12-inch bare-rooted sticks. Now they not only differ widely in both height and shape, but also in their foliage. Some have lost all their leaves, while others are still clothed in an almost full complement of dried leaves. The leaves differ between trees, too. Some trees bear small leaves, and some large. On some the leaves are narrow, on others broad. Even the colours differ, ranging from pale fawn to a rich russet.
On each tree, if you look closely, there are signs of life.
Many of the trees bear these galls - I've always called them oak apples, but apparently they're Marble Galls, product of the gall wasp Andricus kollari.
These galls - the Common Spangle Gall (top photo) and the Silk Button Spangle Gall (lower photo) are caused by two species of Cynipid wasp which have complicated two-stage life cycles. Males and females hatch from Currant Galls formed on oak flowers. The females lay their eggs on oak leaves, and the grubs cause the creation of the galls shown here. When the grubs mature and become adult, the whole generation consists of females who lay their eggs on oak flowers to start the cycle all over again.
Many of the oak trees carry these galls (seen here with bonus ladybirds!) which look just like the Robin's Pincushion galls on the neighbouring wild roses. I haven't been able to find any reference in the literature to oaks bearing Bedeguar galls, but that's what these appear to be.