Scott explains what galls are, and how they're formed.
The Spruce Pineapple Gall is a common example of an irritated plant. (Courtesy Forest Pests)
What if you could get someone else to build you a winter home surrounded by food and completely protected from the harsh elements? Sound good? Well, it must work for an awful lot of insects, because that’s what they do when they make galls in plants.
Galls are leaves, stems, and branches that have grown in a deformed way because of insects. Often, they appear as an odd swelling on a plant stem or branch. There are lots to see if you know what to look for.
Scientists are still learning how galls are caused. The insects burrow into the plant and either physically irritate it or secrete something that affects the way the plant grows. In a way, the plant almost forms a kind of callous around the invader and the developing insect inside ends up with food and shelter.
To date, about fifteen hundred insects are known to cause galls. Over half of the galls identified have been on oak trees, almost all of which are created by wasps. You might be familiar with the summertime oak apple galls that look like ping-pong balls. But there are also blueberry stem, goldenrod ball, and spruce pineapple galls… the list goes on.
To make things more complicated, some gall makers are eaten by other insects, so if you open one up, you might not find the insect that made it, but the insect that ate the insect that made it. What gall!
Winter is a great time to observe and identify these insect shelters. There are no leaves to get in the way and the plant deformities really stand out. Just consult a good field guide for identification.
