Bramble gall

If you find an elongated swelling on the stem of bramble, dewberry or raspberry, it is likely to be the gall of a small wasp, Diastrophus rubi. This one was found on a piece of dewberry, Rubus caesius, after it was cut back to clear a footpath at the nature reserve. The original gall is shown in the extra photograph; this one shows what it's like inside, with a series of spherical chambers, each with a tiny white larva. The galling process, triggered by the female wasp inserting eggs into fresh Rubus shoots, doesn't just make the plant grow this structure to provide shelter for the developing larvae, it also causes special nutrative cells to develop on which the growing larvae feed through the autumn until they pupate and eventually develop into adult wasps which can chew their way out of the gall the following spring.