They are elongated and pear-shaped and have a smooth, shiny surface. A short stalk at the larger end attaches the egg to the bark, and a long, threadlike process projects from the smaller end. Small, yellow, wingless nymphs are about 3 mm long when newly hatched. There are five immature stages. The fifth instar nymph acquires wing pads.
Adults are dark reddish brown and have four wings.
The pear psylla is a pest of only pears and is present in all pear-growing areas of Canada and the United States. The pear psylla secretes honeydew, which serves as a substratum for the growth of a black fungus that gives the tree a smoky, sooty appearance. Foliage may wilt and drop to the ground. Trees that are heavily infested for a long time produce little growth and set fewer fruit buds. Fruit remains undersized, fails to mature and may fall off the tree when only partly grown.