A substantial number of insects, over a thousand, are associated with oak trees, it is one reason why our oaks are so important. Several of these insects lay their eggs on oak trees which then produce galls or deformities. The silk button gall (Neuroterus numismalis) is one such species. Being a bright orange-brown in colour they are one of the more easily found galls as they are quite noticeable (assuming you take the trouble to look to course!). Why the silk button gall? Each gall has a raised rim and if you look really closely, and it is far from obvious in photograph, each cup appears to have been embroidered with silk!
The silk button gall is the work of a small wasp species which lays its eggs in oak leaf buds and when the leaves open and the larvae hatch each larva creates its own gall to live in. There can be hundreds on one leaf! the larvae mature on the fallen leaf and over winter in the leaf litter before emerging in spring to start the process again. It is actually more complicated than that but that is the best I can do in trying to understand the process!