Do you know this culprit?
I was walking in the woods the other day when I came across a gall on this Hamamelis virginiana or Witch Hazel shrub. I didn't have a clue what insect made this gall on the tree so I thought I would do a little research. I found out that it is an aphid (witch-hazel cone gall aphid or Hormaphis hamamelidis) which in a "vampirish" fashion finds a nice juicy intersection of veins and then proceeds to suck the sap from her needle-like jaws. As the aphid feeds on the plant, she is inadvertently jabbing the leaf with her beak. This results in a reaction from the plant which rises up to form a Wilbur Bud** shaped house around her. This is the gall which actually saps sugar and nutrients from the plant that are given to the feeding insect. The galls have a way of tricking a plant into thinking that it is forming a new leaf, which allows the phloem to go into the gall and feeds the insect.
Most plants are not severely affected by the aphids, but some can be. Check out what galls you may find when you are next walking in the woods!
**side bar, if you have never experience Wilbur Buds, I strongly recommend you do so. They are a candy factory in Lititz, PA, and they make the most awesome candy I have encountered!!