Willow Gall

Lately, when out, I've come across a few of these, the leaves looked like a willow tree but it appeared to have a growth resembling a pinecone. At last I discovered it is a Willow Gall. Much like the galls on goldenrod (round bulges in the stem) this occurs when an insect (midge gall in this case) lays a single egg in a willow's terminal bud in spring. Chemicals injected by the female midge mixed with the chemicals exuded by the egg cause the willow to stop the elongating of the branch and instead causes the leaf tissue to broaden and Harden into the shape that resembles the scales on a pine cone. The larvae will then safely grow to adulthood and emerge from the gall leaving no harm done to the tree.