Hackberry psyllids are often called NIPPLE GALL PSYLLIDS because nipple-shaped galls about 3/16 inch wide and 1/4 inch high develop on the underside of infested leaves. They resemble miniature cicadas (about 1/6 inch long) and are a dark, mottled-gray color
The gall, an abnormal plant growth on leaves or stems, results from complex chemical interactions between developing insects and plant tissues. As a gall develops, it becomes a “house” where the immature insect resides. Most infested leaves contain several galls, and host trees apparently do not suffer seriously, although galls are normally considered unsightly.
Adult psyllids emerge from galls in September and can be annoying to people living near infested trees. Psyllids will swarm to houses, particularly light-colored ones, in search of protected locations to pass the winter. They are attracted to lights at night and are small enough to pass through ordinary window screening. In some instances, large numbers gain entry into a home and become a nuisance. Psyllids do not bite people, pets or houseplants — they are pests only because of their unwanted presence.
After the onset of winter, psyllids generally are not active; however, they may mistakenly come out of dormancy on warm winter days and may create a minor nuisance. The biggest nuisance normally occurs during spring, when they break dormancy and fly about indoors, looking for places to exit the structure.