Most galls are caused by cynipid wasps and gall midge flies. The adult gall wasp is a small, stout, shiny
insect with very few wing veins and a purple or black body. Adult gall midges are tiny, delicate flies,
often with long, slender antennae. Some galls may be caused by gall
mites or larvae of some moths.
Galls are distorted, sometimes colorful swellings in plant tissue caused by the secretions of certain
plant-feeding insects and mites. These unusual growths may be found on leaves, flowers, twigs, or branches.
Five species that are common are the honeylocust
pod gall midge, the ceanothus
gall moth, the baccharis
gall fly, the twohorned
oak gall wasp, and the willow
leaf gall sawfly. Another species, the alder gall
midge, Dasineura sp., can cause cupped leaves, thickened or galled along the midvein, because of
a tiny pale larva feeding within tissue.
Most galls are not known to harm trees. Prune and dispose of galls if they are annoying. This may provide
control of some species if pruning is done when the immatures are in plant tissue and before the adults
begin to emerge.