Ever notice strange growths on plants or what appear to be warts on leaves and stems? These might be something called galls. There are many definitions of a “gall”, but today we are talking about “an abnormal growth formed on plants and trees, especially oaks, in response to the presence of insect larvae, mites or fungi.” These strange growths come in all shapes, sizes, colors, and forms.
They can appear to be causing great harm to their host (plant or tree), but most galls are harmless. Younger plants may be affected if their smaller circulatory system becomes blocked by the excess cell growth caused by galls.
In addition to insect larvae, mites and fungi, bacteria, viruses, and nematodes can cause galls too. Galls are often the result of the plants response to insects laying their eggs in the plant’s tissue. They do this to hide their eggs and the plants’ responsive tissue growth provides food for their larvae. Score for the insects!
Scientists still aren’t 100% sure of what causes galls to form. The saliva or the eggs of the intruder are two possible reasons for the plants’ response. Whatever it is, the plants are triggered to release something called phytohormones that begin forming the gall. Phytohormones are chemicals that regulate plant growth.
One thing to note is, if you see a tiny creature crawling in or around a gall, that doesn’t always mean that’s the species responsible for causing the gall to form. Other insects may climb into the gall searching for food.
And, speaking of food, some plants have evolved to protect themselves from hungry insects. Get this…if a plant is under attack by insects, they can release extra chemicals (called volatiles) into the air to attract larger predators that will feed on their invaders. Cool huh? But it gets even better! Some insect species have learned to take advantage of this natural defense. A few gall wasp species have actually figured out how to get their host plants to produce galls that release a sweet, sticky substance which attracts ants that will then protect the gall containing their larvae from other attackers.
The fact that we still don’t know that much about galls is a reminder that there’s still so much to learn about how ecosystems function. Galls are a fascinating subject in nature we can continue to investigate and explore.
Blog post written by Samantha Olsen, intern under Lara Milligan, Natural Resources Agent, revised and edited by Lara Milligan and James Stevenson, Extension Specialist.