Under some of the oak trees on campus, as well as the fallen leaves, tiny pale discs are appearing. Sometimes these are present in large numbers. They show up particularly well on tarmac pavements.
These are button galls which were the subject of a blog by Waheed last year. They are produced by various species of Gall wasp in the genus Neuroterus.
The most common button galls on campus are Common spangle galls caused by Neuroterus quercusbaccarum. These are pale, with clusters of red hairs on the upper side and a slight hump in the centre. The backs are pale with a central depression.
Silk button galls are also frequently seen on campus, although there appear to be fewer this year compared to 2013. These are caused by Neuroterus numismalis. The galls look like doughnuts due to the deep central depression that develops. The surface is protected by radiating lines of bronze hairs that cover the gall.
Less common, but present in greater numbers than last year, are the hair-less Smooth spangle galls caused by Neuroterus albipes. These galls have a distinctly raised margin and can appear notched due to irregular growth.
Detached button galls that lie safely beneath leaf litter through the winter will develop into adult wasps in the spring. However galls that remain attached to decaying leaves will dry out and the developing larva inside will die.
Oak Galls in Britain is a readily downloadable guide in addition to books mentioned in previous gall blogs.