The Robin’s pincushion is a gall caused by the larvae of a tiny gall wasp (Dipoloepis rosae). The female wasp lays her eggs in the leaf bud of a wild rose; the eggs hatch there and the larvae secrete a chemical that causes the leaf bud to grow into a woody gall with a covering of moss-like leaves.
It is also known as the rose bedeguar gall or moss gall. They are widespread; most commonly found developing on the stems of dog-roses (Rosa canina) during late summer. As it matures, the gall acquires a reddish colour.
Each gall holds many larvae, each in its own chamber. The larvae feed on the gall tissues through the winter and emerge in spring as adults. The majority of adult wasps are females which reproduce asexually; males are very rare.
Pictures of gall: Ian Bushell
Picture of rose: DKG