We came across these galls on a wild rose plant last week, and Eliza insisted I do a blog post about them. So here you go.
Insect galls on prairie wild rose – TNC’s Platte River Prairies, Nebraska.
Galls like this are formed when an insect lays an egg on or in a plant and the feeding of the recently hatched larva stimulates excess growth of plant tissue. The result is that the plant creates a little structure that contains both food and protection for the young larva. The most familiar example of this in prairies is the goldenrod gall, which can be seen in just about any prairie containing goldenrod plants. In this case, a wasp laid eggs on this wild rose (Rosa arkansana) plant and inside each of the resulting galls is a tiny white larva.
More galls on the same plant.
For much more information on galls and the insects that create them on wild rose, click here.
The Prairie Ecologist 
SO COOL
(!)
Chris, I have a question. Not related, but important. This year, due to rain, native thistles have really covered our local remnant prairie that we are trying to preserve. An expert has advised us to take them out before they go to seed. Some of the thistles have “pods” on their roots that, when opened, are hollow like seed cases. What is your opinion? Many thanks.
Judith,
Interesting. I don’t know what those would be… I’m also curious to know what thistle species you have and why the expert recommended taking them out. Around here, at least, native thistles don’t tend to cause us any problems and provide great pollinator and other habitat.
They are the Texas thistle. The thistles this year are so abundant that they are choking out other plants. Unsure at this time why our expert recommended taking them out as I did not speak directly with him. I will ask. I agree that they are great pollinators and we were of two minds about this as they are natives. Thanks.
Chris – That’s a great little article, a nice bit of natural history, which I will read and use in my own interpretive work.
Judith – I totally do not get the advice to remove native thistles from a remnant (or even from a young planting) in which they do sometimes, temporarily, dominate. With droughtiness such as has occurred in the region, one should expect opportunistic, annual and biennial, pioneering plant species to have a short “hay day” of a season or two. Digging them out will simply exacerbate problems by creating soil disturbance, and spraying could create other problems, plus denying the multitude of thistle-tissue eating insect species, thistle-seed eating birds and other, thistle-nectar drinking species, and thistle-pollen gathering species, their respective “hay days”. I do wish people would think in the long term and of something besides calendar prairies in instances such as this where it appears the “expert” is not doing so. My advice (with 25 years of tending and planting prairies): Definitely question (or ignore) this expert’s advice.
Thank you James, will do.
The inter-relatedness of living things is amazing!.
Lovely photo of the galls! In the text these galls are attributed to a fly, but the linked paper on rose galls shows very similar galls made by wasps in the genus Diplolepis (see esp. Figs 18 and 24). Is it for sure that the galls in the posted photo were made by a fly? The common spherical gall on goldenrod stems is made by a fly—perhaps the mention of this in the previous sentence triggered “fly” when “wasp” was intended?
Robert – thank you. that’s exactly what happened. I had Fly in my mind and put substituted it for Wasp. I’ve corrected the post now. I appreciate the careful read and correction!
Good Job Eliza!!!!!!
Very interesting, I have never seen galls on roses before. We get them on our bur oak trees, sometimes the downy woodpeckers snack on the larva inside. The ones on the roses are pretty but nasty looking.
Thanks, I found some today too, and took a picture. I didn’t know what they were but suspected they were what they are. Thanks again
Just found some of the galls on a wild rose in our community garden in braham, mn nice to find out about these thanks
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