Many plants have distorted growths caused by insects during the spring. This box elder has Cecidomyid gall midges that cause the leaf curl. If you open it up there will be dozens of small white maggots living inside. The damage is only cosmetic and one a gall is formed the leaf will not develop properly. Look for galls on oaks, maples, ash, and hickory trees.This article was posted in Galls.
Department of Entomology