I have not seen worms yet, it dose not mean I do not have them, or that I have had it in the past.m. I use, at this time, Diatomaceous earth. I put a couple of Spoonfuls in their feed about once a month. I am not sure how often I should treat my girls. But this all the wild birds out there, I am sure they have had to have picked a few up a long tge way.
My problem is mites! It is a Struggle to keep them under control. I have a served what others have said they suspect, when a chicken is sick mites move in. A healthy girl may have them in the hundreds, a sick one in the thousands. Here is a link to info on mites
https://www.backyardchickens.com/a/mites-chicken-pests-how-to-protect-your-chickens-from-mites. I use again Diatomaceous earth. However, I mix it with 7 dust, use a one of those ketchup long noise squart bottles. I can put the tip between the feathers easier to get at the skin. Then I spread it around the pen, and where they take dust bathes or hange up. It has been pointed out several times wood ash works better. Demosthine sugested I check out restaurants that use wood to smoke or BBQ with, give them a galvanized bucket, do to hot ash, to put it in when they clean their ovens/grill.