An online resource based on the award-winning nature guide –

Goldenrod Ball Gall Fly Larva

3-22-13 goldenrod ball gall fly larva IMG_6182The round “ball” that is often present on the stem of goldenrod plants contains the overwintering larva of a fly (Eurosta solidaginis). A year ago an adult female fly laid an egg in the stem of the goldenrod plant. The egg hatched and the larva proceeded to eat the interior of the stem. As it did so, the larva excreted chemicals which caused the plant to grow abnormally, creating a ball-shaped “gall.” If you were to open a goldenrod ball gall today, you would probably find an overwintering larva (if a downy woodpecker or parasitic wasp hadn’t gotten there before you). Within the next few weeks the larva will pupate, and as early as April the adult fly will emerge from the gall, having crawled out the passageway that it chewed last fall. An inflatable “balloon” on its forehead allows the fly to burst through the remaining outermost layer of tissue at the end of the passageway. The adult fly lives about two weeks, just long enough to mate and begin the process all over again.

8 responses

  1. Edward Parsons

    Mary, I also think it is interesting that the larvae has some kind of “antifreeze” to get through the winter.


    March 22, 2013 at 12:53 pm

    • Yes, Edward, I agree — it’s a fascinating adaptation that many overwintering insects have.

      March 22, 2013 at 1:39 pm

  2. I’m so glad to see this detailed photo. We used to call these galls “noggin knockers” when I was a kid, and we disrupted the peaceful resting places of quite a few of these larvae as we picked them and bonked each other’s heads.

    March 22, 2013 at 2:18 pm

  3. Kathie Fiveash

    I did a project many years ago in graduate school of counting goldenrod seeds on plants that had and did not have galls on the stems. If I remember right, the galls did affect the seed numbers, but not a whole lot. Since goldenrod plants in a patch are generally clones, it seemed that the galls did have a deleterious effect on seed production.

    March 23, 2013 at 12:53 am

  4. This was very interesting and informative: Thank you!

    March 23, 2013 at 2:19 am

    • Thank you for taking the time to read my blog, Rick.

      March 23, 2013 at 6:20 pm

  5. Have you ever noticed how the chickadee’s will use this as a food source during the winter months? I have seen them perched on the gall pecking away making a perfect little hole and getting that tasty little bit of protein out of the gall.

    March 23, 2013 at 10:52 am

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s