Oak apples are at their freshest – spongy and sometimes rose-pink – around the time of Oak Apple Day, the 29 May. The day commemorates the Restoration of the Monarchy in Britain on 26 May 1660, when Charles II returned from exile.
The summer generation of the gall wasp Biorhiza pallida, has already emerged. As many as thirty of them live in separate larval chambers in the gall but they’re often joined by parasites and by inquilines: live-in lodgers that don’t attack the resident larvae. The variety of species sharing the gall probably explains the different sizes of the exit holes that they’ve made.
The fertilised females will go on to penetrate the ground and lay their eggs in the roots of oak trees. The larvae usually spend two winters developing underground, each in its own root gall, then emerge early in the year. This early spring generation will all be wingless and all female.
The unfertilised females climb into the branches of the oak and lay numerous eggs at the base of a bud. An oak apple forms from each bud and, as in my photograph, often several of them are clustered together. Males and females develop in separate galls.
These were on a small sessile oak growing by the towpath alongside the Calder & Hebble Navigation, downstream from Horbury Bridge.
It’s as if someone’s thrown a switch and we’re suddenly in the peak of springtime. In the last two weeks we’ve had a covering of gravel-sized hailstones and just last weekend the crowds were braving wintery showers to cheer on the Tour de Yorkshire cyclists. This morning as we follow the towpath to the Navigation Inn (which is still struggling to get fully up and running after the December floods) we’ve got peacock butterflies and orange tips flying alongside us. Greater stitchwort, dandelion and green alkanet are freshly in flower.
A canal side oak is bursting into leaf and amongst the catkins on its branches we spot a few oak apples, made by the gall wasp Biorhiza pallida. The wingless unisexual generation of this gall wasp has spent the winter developing in galls on the roots of the tree then emerged and climbed the trunk to lay its eggs on the buds. The buds develop into the reddish spongy oak apples and from these the bisexual generation will emerge.
A blue butterfly (holly or small blue?) flies up from the rock face which creates a south-facing sun trap at Addingford Steps. On the River Calder near the old Horbury Bridge woollen mills two male goosanders are diving.
A lapwing swoops over the Strands where I drew in the aftermath of the winter floods. There’s a warbler in the tall grasses. From it’s song Barbara thinks it’s a sedge warbler, from it’s appearance – not streaky – I took it to be a reed warbler. But I’m struggling to get a decent view with my little monocular: I must bring binoculars next time!