Lime Nail Gall Mite (Eriophyes tiliae)

I spotted these growths all over the lower leaves of a nearby lime tree. They are made by microscopic Lime Nail Gall Mites (Eriophyes tiliae) which feed on the sap in the leaves while also injecting chemicals that cause the leaf-cells to multiply and enlarge, thus deforming the leaves. The mites over-winter in the tree bark, moving to the foliage in the Spring.