Sycamore Leaf Galls

My back is improving - and we did manage a gentle walk through the woods this morning. Taking everything easy at the moment...hoping for steady improvement.

I found a sycamore tree with a lot of leaves covered in the small red ‘blobs’. It appears that they are caused by a small mite. The galls develop where the mite feeds on the leaf. The female mite then lays eggs inside the structure and the developing larvae feed off the contents of the gall. It appears that it is not harmful to the tree.