The night of August 19, 2022 some loud thunderstorms rolled through our area. The next day we saw deer in our backyard with a lot of weeds stuck all over their coats. The doe and her two fawns (which we frequently see) were covered with the stuff. One of the fawns looked like it was wearing a weedy hat.
I compared it to pictures on the web and it looks similar to Virginia Stickseed (Beggar’s Lice), a common wildflower in Iowa. I’m not sure though; I’m definitely no botanist.
On the other hand, Beggar’s Lice tends to be pretty common where the deer population is dense—because they won’t eat it.
Maybe the loud storms scared them into running through the burr weed patches.
Update August 25, 2022: Here’s a picture I took yesterday of the deer after a week. They’re still festooned with Beggar’s Lice.