Hackberry psyllids pron. SILL-ids are a genus of tiny, planthopper-like bugs. As larvae, they develop within the leaves, twigs, buds, or bark of hackberry trees. The trees form warty galls in response to their presence. In the fall, tiny adult hackberry psyllids cling to window screens. Most have brown-and-white mottled or spotted wings, while at least one species has solid brown wings.
They can walk but they can also jump. Estimates range from 7 to 13 species. One commonly encountered group — whose members form galls on hackberry leaves, as opposed to leaf stems, buds, twigs, or bark — may include four to seven different species that have traditionally all been considered the single species P. Looking at their bodies, there is no discernible difference among them, but they produce galls with different shapes: some are like rounded cones or disks, some are like indented mushroom caps, some are like pudgy doughnuts, some are knobby like nipples; and the nipple galls may be hairy or glabrous smooth.
One type makes inflated, blister-like pouches within the leaf. Genetic testing will probably sort out these various species.
Similar species: In North America north of Mexico, there are nearly 80 species in the family Aphalarida. Globally, there are eight families of insects in superfamily Psylloidea, and all are usually called psyllids or jumping plant lice. Expanding outward to less closely related groups, psyllids are in the same suborder as aphids, scale insects, mealybugs, whiteflies, and the phylloxera insects you may have heard of the notorious grape phylloxera that threatened the global wine industry in the late s and remains a serious pest of grapevines.
Hackberry psyllids occur anywhere there are hackberry trees, which means they can occur nearly anywhere in our state. Most people notice them — the big knobby galls, and the adult psyllids clinging to window screens — in late summer and fall.
