Andricus kollari, also known as the marble gall wasp, is a parthenogenetic species of wasp which causes the formation of marble galls on oak trees. Synonyms for the species include Cynips kollari, Andricus quercusgemmae, A. minor, A. indigenus and A. circulans.
Andricus kollari
Oak marble galls showing two stunted and two normal-sized examples
A developing oak marble gall
An oak apple gall; often confused with the oak marble gall: the brown areas are scale remnants from the bud.
Galls or cecidia are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or warts in animals. They can be caused by various parasites, from viruses, fungi and bacteria, to other plants, insects and mites. Plant galls are often highly organized structures so that the cause of the gall can often be determined without the actual agent being identified. This applies particularly to insect and mite plant galls. The study of plant galls is known as cecidology.
Oak artichoke gall caused by Andricus foecundatrix
Artichoke gall cut open to reveal wasp larva
Knopper gall caused by Andricus quercuscalicis
Oak gall caused by Neuroterus albipes forma laeviusculus