Weekly “What is it?”: Leaf galls
As an ecologist and often the token “outdoorsy” person in any given crowd, people often point to a plant or animal or describe something they’ve seen and ask me, “What is it?” I relish these small opportunities to teach my family and friends about the fascinating things they can find in nature. To that end, I decided to share the answers to some of those questions in a weekly blog post. The “Weekly What Is It?” will include a new photo and explanation every Wednesday. This week, we’ll discuss a fascinating little phenomenon that I’m often asked about during trail hikes.
Insect galls are hard, three-dimensional growths on the leaves or stems of plants. While galls can form on many species of plants, typically (60% of the time) they are found on oak trees and created by gall wasps that have laid eggs into the plant tissue. Much like human skin reacts to a splinter or insect bite by swelling around it, plant cells respond to this foreign tissue by growing a gall around the expanding egg sac to protect the plant. Insect larvae eventually feed on the gall tissue until they’ve reached adulthood. Many galls have small pinholes, a sign that the adult insect has emerged and the gall is empty. Each gall-laying insect has its own characteristic shape. The gall wasp creates one (see photo) approximately a half inch long and spherical.
Another commonly seen gall is that of the swamp bay (Persea palustris), a tree that I’ve never seen without many green, oblong galls wrapped into the curled leaves.While strange looking, galls rarely cause problems for the plants and are an example of commensalism, a relationship in which one organism benefits while the other is neither harmed nor helped. The word “gall” means “bitter”, a reference to the taste of these tannin-filled growths.If you have a mysterious “something” that you’ve always wondered about, email me a photo or description at firstname.lastname@example.org, and hopefully it will be featured in a future post.