Some of the ground ivy Glechoma hederacea leaves in my garden are pocked with white-rimmed craters reminding me of rivet washers on jeans. On closer examination, there are hairy green columns also present on some leaves. These are caused by the fly Rondaniola bursaria. Each column, known as a “lighthouse gall”, contains a single larva which falls off the leaf in late summer leaving the hole.
Robert Homan, the GNS county recorder for plant galls, confirmed the identification and says that it seems to be a good year for “lighthouse galls”. There are a lot on beech and lime, though these are caused by other invertebrate species. He would no doubt appreciate more records.
Posted on behalf of Juliet Bailey.