The gall of goldenrod
Take a walk in a meadow this winter and enjoy the beauty around you. Notice last summer’s wildflowers: Queen Anne’s Lace, mullein, milkweed, buttercup, and goldenrod, to name just a few. They stand proud above the snow. But what are those round balls in the goldenrod stems? Is that where ping-pong balls come from, or what?
You’d have to be desperate to use goldenrod galls for ping-pong. These small round growths in the stems of the plant are actually homes for the larva of the goldenrod gall fly! Touch one and discover how hard it is – much tougher than the supporting stem.
Inside is a small cream-coloured worm, the larval stage of the fly. When the weather warms in spring and new goldenrod plants are starting to grow, the larva turns into a pupa. The adult fly emerges from a tunnel through the gall that it built the previous fall. They are not good flyers, so they usually walk to a nearby goldenrod plant to find a mate.
The female lays her eggs in the stem using a thin tube called an ovipositor, which literally means “one who deposits eggs.” In about 10 days the eggs hatch. The larva chews the developing stem tissue. Its saliva makes the plant produce the characteristic round gall which provides it both food and protection.
At the end of the summer the larva excavates its exit tunnel, scraping through the gall right to the edge of the outer wall. As autumn temperatures cool, the larva produces concentrated glycerol in its tissues. This insect-anti-freeze protects it to minus 40C. Warmer spring temperatures trigger the transformation into a pupa, and the cycle repeats.
However, many larvae do not survive to adulthood. These nutrient-rich nuggets often become a winter meal for chickadees or downy woodpeckers. The birds peck into the hard gall tissues to extract these tasty wholesome tidbits. There are also other insects that lay their eggs in the larvae, and those parasites consume the host goldenrod gall larvae.
Look closely at any goldenrod galls you find. Has a bird already found a tasty snack? Are there a lot of galls in the area? Be amazed that there’s a little worm inside that’s better able to get through winter than you are. Perhaps you’ll take an empty one that’s been pecked open home for a fun game of ping-pong!
Nancy Melcher is The Nature Nut. Send details of your sightings or questions about the natural world to: general@melcher.cx