These turn reddish in the fall and are commonly known as oak apples. Light lentiform galls on the undersides of the same leaves are induced by "Neuroterus quercusbaccarum"; darker ones with bulging edges are formed by "Neuroterus numismalis." Also striking are the galls of "Cynips longiventris," which likewise can be found on the undersides of leaves, and are recognizable for their spheroidal shape and irregular red streaks. The oak potato gall wasp ("Biorrhiza pallida") has round galls that grow to about 4 cm. These are known colloquially as oak potatoes. The latter type of gall is induced by this type of wasp not on the leaves, but on the roots of the oak. On the buds of young oak twigs, one can often find the hard-shelled galls of "Andricus kollari" and "Andricus quercustozae." Galls do not cause significant harm to oak trees.