On investigating plants throughout the summer, it is not unusual to come across a bizarre looking growth on a plant, many times looking much like a tumor or a wart. These are galls and they are produced by a variety of parasitic organisms such as viruses, fungi, mites and insect grubs.
Galls come in an astonishing assortment of shapes, colors and sizes, depending on which organism created them and which plant is being parasitized. Gardeners may bemoan the appearance of these funky growths. But for the most part, they don’t really harm the plant unless it is already sickly or is heavily laden with galls, they only render it a bit unsightly to look at.
The invading organism releases a substance which irritates the surrounding plant cells which begin forming a microhabitat for the parasite to live in. Insect galls will often have nutritious starches and other materials which may insure that the grub remains in one spot and doesn’t entirely devour its host.
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The above picture shows a small clump of galls on a wild grape vine in my back yard. They are likely the product of grape midges that hatch from eggs laid by the mother inside the stem of the vine which then forms the gall. There are a variety of grape midges each with its own life cycle. The vine itself appears uninjured and as long as the damage remains minimal, I will leave it be.
This particular gall was found on a non spiny member of the thistle family (not sure of identity). The gall extends several inches along the stem, swelling it but not apparently interfering with the growth of the weed as it managed to produce flowers. Until I can firmly identify which plant it is, the identity of the gall maker will be uncertain.
This odd bulbous growth found on a jewelweed plant is also a gall. It is formed by the larva of the jewelweed gall midge. The egg producing the larva is planted by the mother into a forming flower bud which then creates this odd structure looking much like a Christmas ornament. Once it has matured enough, it will chew its way out, drop to the ground and winter over.
Galls can take many whimsical shapes, some looking so much like part of the plant that if you aren’t familiar with the species, you might not realize you are looking at a plant gall. One is the willow pinecone gall which resembles its namesake. It looks quite ordinary until you recall willow trees don’t have pine cones. Oak apple galls often look so much like apples, you could be forgiven for thinking it was an actual fruit. But a closer look reveals its true nature, an oddly structured home for the little grub inside.
It’s easy to pitch a hissy fit when you see these strange formations on prized plants in your garden. But for the most part they are harmless. Many of these larva and mites hide inside the plant to avoid predators such as birds and other insects who would gladly chow down on them if the opportunity presented itself. What looks like a nuisance to you is actually lunch to somebody else. If you really have to, just pinch off the leaf or odd growth and remember it’s merely another startling reminder of some of the astonishing adaptations to be found in Nature.
