The Gall of it

The storms in early January battered my patch and the surrounding area bringing down a few trees. One such trees was one of the old willows beside the path. Unfortunately for the farmer who is losing crops left right an centre from wider paths due to social distancing has lost even more crops as people are forced to make a wide detour around it. 

Luckily, for me the fallen tree gave me an option to investigate some interesting growths on the upper wisp like branches. During the winter it is easy to spot strange dark masses at the tops of trees. Often these attract my eyes thinking they are small birds sat in the tree.

Getting close up the growths very much looked out dried out clumps of moss.

This straggling masses are woody to the touch and emanate from the wood beneath. It could have been a moss but this doesn't feel right and in this wet weather should have been a nice dark green. I little research led me to one possibility Mossy Willow Catkin Gall.

Galls are created by insects, mites and viruses that cause undifferentiated cell growth at specific points. Many people will be familiar with spangle galls on leaves of the masses that grown on acorns. Many are caused by ichumenoid wasps which lay there eggs inside this mass of tissue.

Little is known about the Mossy Willow Catkin gall in fact its name describes pretty much all we know. They look moss like with fibrous projections that in the summer are a rich green colour. They are found on willow trees and grow from catkins explaining why they are seen from the thin twigs upon which these reproductive parts grow.

It was originally believed thy were caused by mites however it is now suspected that the mites are merely associated with the galls and that the primary cause is a virus.

Catkins are sensitive and delicate structures and those infected seem to be high up in the trees near the tops this leads me to suspect a wind borne pathogen that is carried on the breeze which infects exposed catkins at the top of the trees where there are less leaves to shield it from the breeze.

Galls are fascinating as are the creatures that make them and in the summer I will look for more on the leaves and record the species.

For more information on Galls go to: https://www.britishplantgallsociety.org/index.html