We have recently been finding galls on our hikes. Simply put, galls are abnormal growths of tissue on plants. Galls can be caused by a number of things, insects, fungi, bacteria or even other plants. We decided to learn more about our gall finds by cutting them open.
The first gall we found was on a goldenrod plant. We learned that there are three different types of galls that occur on goldenrod.
- A bunch or rosette gall is created by the Goldenrod Gall Midge (Cecidomyiidae).
- An elliptical gall is made by the Goldenrod Gall Moth (Gnorimoschema)
- A ball gall or apple gall is the work of a Goldenrod Gall Fly (Eurosta solidaginis)
Our gall looks like a ball, so we knew it was created by the Goldenrod Gall Fly.
It was fairly easy to cut open with a knife. Once the outer skin was broken the inside was easy to work through.
This is what we found!
Our research led us to break the life cycle of the Goldenrod Gall Fly into six stages.
- The adult fly lays eggs in the stem in the spring or early summer when the plant is growing quickly.
- The egg hatches and the larva bore into the stem and starts eating the plant.
- The larval activity and chemicals injected into the plant stimulates the plant to produce more tissue at that location thus forming the gall.
- In the fall the larva creates an exit tunnel that extends up to the surface of the gall but stops before breaking the outer layer. You can clearly see this in the picture of the open gall.
- The larva goes back to the center of the gall to over winter.
- In the spring it pupates (which is the stage we think we observed above) and in late spring to early summer it emerges as an adult.
The adults do not eat and only live from 10 – 14 days. Just long enough to mate and lay eggs for another generation.
We moved on to the galls we found on the oak trees in the forest. We had an older one and a fresh new one (cut from a branch that needed to be trimmed to clear the trail better).
In this case multiple eggs had been laid in one stem by what we learned was a Gall Wasp. We think these are the work of Andricus Kollari according to the pictures we found on wikipedia.
In this new green one you can see the small eggs or larva. We are not quite sure but they were not moving so we assumed they were the eggs.
The multiple exit tunnels can be seen in this older one.
These took a little more work to get through with a saw and I would highly recommend the use of a vice for safety when cutting harder galls like these.
There are many types of galls out there to discover. I will try to dig up some pictures of others we have found to post to the Flickr group.
Have you seen any? We would love to see or hear about them!