Parasites in the Park: Galls

Sagebrush Gall, made by the Sponge Gall Midge (Rhopalomyia pomum)

Say you are on a hike and feel dehydrated and run out of water, but you come by a reasonable water source. You gather some water in your water bottle and replenish your thirst. In a couple of hours you get an upset stomach and pass the amoeba-infested water by diarrhea and feel better shortly afterward. This is a natural process of a parasitic relationship. Both animals and plants can be involved in this kind of relationship. If you have ever seen an abnormal-looking part of a plant that resembles a tumor, you are not seeing things. These strange formations are called “galls,” growths on plants that are caused by parasitic organisms. More specifically, the plant tries to separate the parasitic larvae from the rest of itself by forming this tumor-like cavity where the larvae can live and grow. The gall-maker gets protection and food from the gall, while the plant spends its tissue and energy forming this gall. There are over 1,000 species of gall-forming insects, mites, nematodes, bacteria, and fungi that produce these formations as part of their regular life cycle. The galls can be formed on any part of the plant, including roots, stems, fruits, and leaves. While scientists are still studying how the organisms cause the plant cells to divide abnormally to make the galls, biochemical secretions are believed to play a crucial role in gall formation.

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