Elm Cockscomb Aphid Gall

While walking near Rochester Falls Conservation Area near the Platte River Joey found these odd looking formations on an elm tree. The tree was covered with them, almost every leaf had at least one of these projections and many leaves had several. I could tell they were galls, but I had no idea what kind, or for that matter what insect had created them. I did however know who would be able to identify them. I snapped a picture and as soon as we returned home I sent an image via facebook to Charley Eiseman. He is the author of the blog Bug Tracks and the book Tracks and Sign of Insects and Other Invertebrates: A Guide to North American Species, which I highly recommend as a field guide. Within a short time he responded and correctly identified these odd looking galls as Elm Cockscomb Aphid Galls. These galls are caused by the aphid Colopha ulmicola. 

 They are found on Red and American Elm trees and do not cause any significant damage to the tree, they just look a bit unsightly in large numbers.  The tiny aphids form the galls and may be seen on underside of the gall. As the gall matures it will change color from a burnished red color to brown that resembles the flower this gall is named after. Each gall measures approximately 1 inch in length X 1/4 inch high. Once the aphids leave the gall, they will begin feeding on grasses.  They will return to the tree and lay eggs between the bud scales that overwinter.Because they do not cause lasting damage to the tree no treatment is recommended to kill them.