Goldenrod Gall Fly

Eric Bak, MAEAP Technician

Back in August we learned about ragweed and goldenrod producing pollen and what it does to our allergies.  Let’s take a closer look at the lesser problematic plant, goldenrod. 

Goldenrod with gall

How many times have we really looked at a goldenrod plant?  Have you ever noticed a round ball or growth in the top one-third of the plant stem?  This is called a gall.  This gall is produced by a goldenrod gall fly, which is related to the fruit fly, and is in the same family.  The fly’s eggs are inserted near the developing buds of the plant.  After hatching, the larvae migrate to an area below the plant’s developing buds.  Then they cause the plant’s tissues to form into the hardened, bulbous chamber around them, called a gall.  These galls serve as a food source for the larvae and shelter from rain, wind, ice and predators.  This time of year, the black-capped chickadee and downy woodpecker will target these galls and eat the nutritious larvae inside.  The larvae are also host to a few different parasitic insects.  If the larvae survive through the winter, they emerge to repeat the process all over again. 

So, the next time you see children picking these round galls to use in their sling-shots, remember how Mother Nature had a hand in making them. 

Inside of a gall