Volker, Thanks for more information on hog bristles. There are also cheap disposable paint brushes labeled as "hog bristle -made in China' that might serve as a source. But as you noted about the critters that snacked on your chamois brush, I'm also a bit obsessive about not using natural materials as much as possible because they either get eaten, moldy or brittle exposed to light. You read in my comment on Russ's post about modeling raw, aged wood that some little critters ate the silver sheen off the driftwood sticks I'd carefully collected.
That said, I have and will continue to use various natural materials when they offer the best results.
Here are a few tall weeds in a marshy area of my layout that are simply individual hairs from a white tail deer. I found them on a walk in the woods and preserved them with a bit of boric acid after consulting with a taxidermist. The hair has a naturally mottled color and tapered tip that look convincing, though exactly what it represents isn't clear. So far (10 years) nothing as eaten them
The short marsh grass is synthetic and the bottom of each hair was simply dipped into yellow carpenters glue and held briefly against a strand of the synthetic for a few seconds until it stuck.
This is a terrible photo, but it's the only one of that area at present. The mix of the short yellow grass and taller stems look like a marshy area near here, so I'm pleased with the results but wouldn't try the deer hair for the reeds because once bent they break and fold over.