DE is usually used to prevent trouble from bugs. It is said to kill mites and other arthropods (love that word - it includes insects, spiders, mites, all kinds of things) that can be pests in the livestock shelter. You don't want to inhale it, but it's fairly benign stuff.
I carefully sprinkle a bit around where the wall and the floor meet, and under the watering station, under the bottom bale of shavings, tiny tight little places that bugs may want to congregate. It gets into their breathing apparatus and chokes them, I believe.
It is for the ducks' environment, I don't put it on the ducks due to the respiratory concerns.