Question
Hi, I have what I believe to be a hickory tree that is at least 35 years old.  It has these dark, round growths on many of the branches.  They seem to be about 2-3" diameter and arranged singly along branches.  What do you think this is, and what should I do about it?  Thanks

Answer
These are gall insects caused by a small wasp. The insect lays its eggs on the twig and secretes a chemical that causes the cells of the twig to grow over the egg forming the gall. When the egg hatches the wasp flies away leaving the woody gall. These cause no real health problem to the tree. There is no need to treat the tree. I would not worry about these gall since they will not harm the tree.