Download a free copy of the Adobe Acrobat Reader. On warm afternoons, the outdoor air becomes filled with swarms of these small flying insects. They gather on exterior sunny surfaces, cluster on window screens, accumulate on freshly painted surfaces, and invade home through open windows and doors. Psyllids overwinter wherever they can find shelter in buildings and crevices of trees, etc. The immatures develop on hackberry leaves during the spring, and cause formation of the familiar nipple galls on the undersides of the leaves.
Adults reach maturity and emerge from the galls in the fall just before leaf drop.
Tree damage from the galls does not appear to be of serious concern. If hackberry trees are common in your neighborhood, you will likely experience this problem from time to time. When windows are open on warm fall afternoons, these insects will come through the screens to create an indoor nuisance. Upon outdoor inspection, you may find them clustered on sides of the building nearest the trees. They will disappear when cold weather arrives, but the problem reoccurs each year to some extent as long as the host trees are nearby.