I treated my chix for internal parasites(1% ivomec drs. instructions) and noticed lice on one of my cleanest looking girls(I hate saying the word lice!!!OOOOH) anyhoo- waited for dry weather to dust them (appx. 5 days after worming) and the girl with lice had NO visable parasites on her skin. I have read, on here, that the oral wormers will not affect external parasites but I wonder now.