Sheer gall

The gall wasps have been busy among the oak trees this year. I spotted four different types on one walk yesterday. 

First up we have the marble gall or ink gall.

These are caused by a tiny wasp, Andricus kollari. The spheres start off green but brown with age and will often remain on the twigs for a year or more. You can tell that the wasp has fled its larval home when you see tiny holes in the sphere. These were once highly prized in the production of a non-fading black ink.

   

Next up is the knopper gall.

The knopper gall is a relatively new arrival in the UK as the wasp only arrived in the 1950s. It’s found mostly on pendunculate oaks (Quercus robur) - also known as the common or English oak. The wasp, Andricus quercuscalicis, lays its eggs on the freshly pollinated flowers of the oak, causing the offspring to deform the acorn. This gall develops over the summer and falls to the ground in autumn when the larvae emerge. 

Then we have the artichoke gall.

Also known as hop galls due to their resemblance to flower of the hop plant, these are caused by the wasp Andricus foecundatrix . Using its sharp ovipositor, it lays its eggs in the leaf buds of both the pedunculate oak and the sessile oak (Quercus petraea). 

Photo: David Nicholls

Finally there's the cherry gall, created by the Cynips Quercusfolii that lays its egg on the surface of an oak leaf - usually on a vein. It creates a round swelling that eventually goes red, like a cherry.

There are lots of other types of gall but it was a treat to see four in one day.