As part of the Wanstead Wildlife Weekend, James Heal will be exploring the mysterious world of plant galls
What do the Magna Carta, the American Declaration of Independence, the notes of Leonardo da Vinci and the music of Bach all have in common? An answer (there may be more) is that they were all written with ink made from plant galls. More specifically, the ink made from marble galls caused by the wasp Andricus kollari.
A plant gall is an abnormal growth produced by a plant under the influence of another organism. It involves enlargement or proliferation of host cells and provides both shelter and food or nutrients for the invading organism. This definition is from British Plant Galls by the renowned cecidologist, Margaret Redfern.
I am a local amateur naturalist with an interest in a range of different invertebrates. I’m not quite a pan-species lister (someone who records wildlife across all the taxa), but I do have an interest in a range of different groups: birds, bugs (Hemiptera, the ‘true bugs’) and plant galls are probably my three favourite groups of organisms to record and study.
Take an oak tree (Quercus robur or Quercus petraea). You may have noticed the hard spheres of marble galls (the ink producers) on retarded saplings (they seem to do less well on healthy, mature trees), strange sticky growths on acorns (knopper galls caused by the wasp Andricus quercuscalicis) or small, colourful discs on the underside of oak leaves caused by one of three different wasps in the genus.
Gall wasps (think tiny black or brown flying creatures, not big yellow and black ones) create some of the most elaborate galls. How about Robin’s pincushion? The messy explosion of red, orange and yellow hairs on roses. But wasps are not the only gall causers. The entire study of plant galls is named after a family of gall midges (flies): cecidology from Cecidomyiidae, and there are many midge-induced galls including the ‘pocket and stitching’ type galls on ash leaves caused by Dasineura fraxini.
Gall wasps and gall midges are small insects, but some large gall structures are caused by truly microscopic invertebrates, including gall mites. Have you ever seen pointy red nail galls on lime (Tilia) leaves? If you haven’t, they are just starting to develop now and can be found, for example, on the long avenue of lime trees stretching from Bushwood down towards Davies Lane in Leytonstone. They are caused by the mites Eriophyes tiliae. Inside each nail gall are hundreds of hairs with a hairy opening on the underside of the leaf. Inside the gall, amongst those hairs, live miniscule, worm-like mites.
If you would like to discover plant galls for yourself, I encourage you to get closer to plants, particularly the leaves (but certainly not exclusively leaves, as galls also affect buds, fruit, catkins, flowers, twigs, roots and even the trunk). And if you would like to learn more techniques for finding and identifying them, I will be leading a walk focusing on galls (and other invertebrates that we might find on plants) on Saturday 22 June as part of the Wanstead Wildlife Weekend.
I will leave you with one final fact about plant galls. Believe it or not, even plants can gall other plants. The most famous being mistletoe (Viscum album), which grows on trees of various species and derives all of its nutrients from them.
For more information on Wanstead Wildlife Weekend events, visit wnstd.com/wild24