This week: What Are Those Funny-Looking Acorns?
Hello!
Sometimes, you see things on trees that don’t seem right. Take, for example, little round growths on oak twigs. For a second, you might think they are acorns. In reality, they are a kind of insect called gall wasps (Cynipidae). Don’t worry—they are usually not harmful to the tree and there’s no reason to interfere with them. They are another way that oaks provide habitats for other life forms!
Quite a few types of galls exist. The photo below shows Rough Oak Bulletgalls (Disholcaspis quercusmamma) on a Swamp White Oak (Quercus bicolor). Funny enough, these types of wasps are often named after their galls, not their bodily characteristics. This particular gall seems to be named after musket balls.
Gall wasps have a fascinating lifecycle. Asexual female wasps lay eggs on leaf buds early in the season, forming tiny galls that go unnoticed. They hatch to become male and female wasps. This new generation of female wasps lays eggs on branches. This tricks the tree into becoming its host, so the tree redirects some of its cells to form a protective coating around the eggs. These are the galls we mistake for misshapen acorns or some kind of tree disease.
More importantly, these galls provide a home and food for the immature wasp. The gall protects the wasp by secreting honeydew. This sugary substance attracts ants and wasps (like yellowjackets) who chase away other parasitic insects and hungry birds. Finally, the galls hatch. This generation has only asexual females who will lay their eggs on leaf buds, and so the cycle continues. Strange creatures!
Elsewhere:
iNaturalist is hosting a free webinar on January 22. It will show you how to help scientists collect seasonal data about plants and insects. Who doesn’t love phenology? Register here.
Have a great week,
Julie