A man dropped by the office last week and brought with him a rather interesting find. He had been out for a walk and came across something rather odd on a young and at that moment, unidentified tree. It turned out he had found some galls on a young oak tree that was made by an oak gall wasp. So what is a gall? A gall is an abnormal growth produced by a plant under the influence of an organism (virus, bacterium, fungus, plant or animal); it involves enlargement and proliferation of plant cells which provide shelter and food or nutrients for the gall maker. Sounds a bit like something from a Sci-Fi film don’t you think?

Oaks, especially the native Sessile and Pedunculate Oak species are the host plants for more than 30 species of gall wasp. The plant produces abnormal growths in the larval stage of these insects and the growths envelop the developing larvae. Different species of female gall wasp lay eggs into different parts of the oak tree such as flower buds, acorns, vegetative buds and roots. Once they hatch, these grubs secrete chemicals that reorganise the oak’s normal growth processes. So instead of the oak growing normally, it begins to produce these gall structures which grow around the developing grubs.

They have some quite interesting names including Oak Artichoke Gall Wasp, Silk Button Gall Wasp and Oak Apple Gall Wasp. As you might imagine the artichoke one looks like an artichoke and the apple one looks like a wee rosy red apple. Galls can be found on all sorts of plants from thistles and knapweeds to spruce and yew trees. If you didn’t find the above too galling, you might be interested to hear there is a British Plant Gall Society.

Laura Preston – Falls of Clyde Ranger, Scottish Wildlife Trust
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