Cola-nut galls[1] develop as a chemically induced distortion of leaf axillary or terminal buds on pedunculate oak (Quercus robur) or sessile oak (Quercus petraea) trees, caused by the agamic gall wasp Andricus lignicola (Hartig, 1840) which lays single eggs within leaf buds using their ovipositor.

It grows up to about 10 x 8 mm and is at first green, rapidly changing to grey-brown, with light red patches where the original bud scales have separated.

The imago of the agamic phase emerges in early summer following the gall's inception.

The bisexual generation gall is very similar to that of A. kollari, effecting the live bud of Quercus species[2] and has only been seen under culture conditions (1975).

[3] Removing and destroying cola-nut galls before they dry and the wasps emerge may help to reduce an infestation.