Friday, 31 July 2015
Galls on willow
A follow up to the last willow posting.
We have white willows AND crack willows at Filnore Woods and at this time of year both species are likely to produce galls. This sprig of willow not only sports a fine Mossy Willow Catking Gall, but also some red blister galls on the leaves.
The Mossy Willow Catkin Gall, which is really a modified catkin, is probably caused by a virus but science has not yet tracked it down. It used to be thought that it was caused by tiny mites but it is just that large numbers of mites and insects choose to live in and around these galls.
The blister galls on the leaves are the trees reaction to being injected with eggs by the female Willow Redgall Sawfly (Pontania proxima), which is like a tiny black wasp. As soon as she has sawn a slot and placed her egg in the leaf, the tree produces this red blister gall, which the sawfly grub feeds on from the inside until it is time to pupate.