Gall maker: Pachypsylla mamma Riley; a species of jumping louse or psyllid (Order Homoptera, Family Psyllidae). The hackberry is a favored gall site for the Pachypsylla genus, and many hackberry leaves are often badly deformed by infestation.

Shape and Size: Galls are roughly "nipple" shaped, and may be very elongate or roughly spherical. Approx. 0.4 to 0.5 cm in diameter.

Location: Occur on the underside of Celtis leaves, usually in summer.

Color: Greenish to yellow-green, decaying to brown when open (see photo).