Ooooohhhh, such gall!
You’ve probably seen some unusual round growths, about the size of a ping-pong ball, in the stems of goldenrod plants. These balls are called galls and they’re the homes of some baby flies. However, other insects also use plants as a nursery for their offspring.
The female Goldenrod Gall Fly lays eggs in the stems of the plant in the spring. The eggs hatch into tiny cream-coloured larvae several days later, and they begin to feed on the tissue inside the stems. Their saliva makes the goldenrod plants grow a hard rounded structure that houses the developing larvae. In the fall they chew a small tunnel through the gall to serve as their exit the following spring.
The larvae spend the winter inside, protected from the cold by the gall itself, but also by making antifreeze to prevent their tissues from freezing. They may become food for black-capped chickadees or downy woodpeckers, as these birds can peck through the gall to pull out the nutritious larvae inside. Those that survive will pupate in the spring and push out of their exit tunnels. They’re not good fliers and spend most of their 10-to 14-day lives walking on nearby young goldenrod plants to find a mate, and lay eggs.
Another insect makes its home at the top of the goldenrod plant. Goldenrod Bunch Gall Midges lay eggs in the top leaves. The larvae secrete chemicals that make the stems stop growing taller. Instead, they grow more and more leaves from the same spot, making large rosettes that provide shelter and food for the developing larvae. These tight clusters of leaves also make homes for others, like spiders and other midges!
A different midge is responsible for making willow shrubs grow galls that look like little pinecones. Willow Pinecone Gall Midges lay eggs in willow buds at the ends of the branches in springtime. Chemicals injected by the females and secreted by the eggs and larvae cause the stem tissues to broaden and harden into the shapes of pinecones.
Photo by Nancy Melcher
I’ve found all these galls while walking on the local trails, including the Barton Trail and the Uxbridge Countryside Preserve. They don’t harm the plants and provide unique homes for insects which in turn provide food for our local birds, both in the summer and winter. Nature can be fascinating if you stop and look closely!
Nancy Melcher is The Nature Nut. Send details of your sightings or questions about the natural world to: general@melcher.cx