Rose pea gall

The rose pea gall on the leaves of the Dog rose (Rosa canina) can be in two forms, either as a spikey form, which can have 2 to 6 spikes and houses the cynipid wasp D. nervosa or the rarer D. centifoliae or as a smooth spherical form (the one spotted here) which can house either Diplolepis nervosa or D. eglanteriae .

The causer wasps need to be reared and keyed out to species to be certain of which one you are dealing with due to the fact that they all can occupy smooth galls. The galls shape instead appears to be more related to its position on the plant than the species creating it. Smooth galls tend to appear on the top smooth part of the leaf, whereas the spikey galls tend to be formed on the underside of the leaf.

Each gall is a hollow, fleshy nursery chamber for a small white grub, the larva of the Diplolepis nervosa or D. eglanteriae gall wasp, which feeds on the chamber wall. The galls appear to detach from the leaves before leaf fall and will lie in the leaf litter until the grub pupates and emerges as the small adult wasp, only about 4mm long. If the gall is on the underside of the leaf or otherwise shaded from the sun then the gall of either form will remain greeny white with maybe a slight flush of pink, however if the gall is exposed to the sun then it will turn a deep red colour before it matures.