How do you tell if hens and hen househave mites?

Chickens and their environment should be treated for mites regularly. I don't know how you can tell if they have them...just assume they do. Was raised on chicken farm and that was one thing we did on a regular basis..spraying the roosts, nests, etc. Check with your county agricultural extension office on the best pesticide to use. Do not just use any pesticide as you could harm the chickens.allways assume they do and treat them. Put diatamatious earth in a paper bag stick chicken in holding it by the legs . shake. Im not kidding.okay first pick up one of your chickens woith gloves or so on.. Then look under there feathers. You should see little white or dark like things moving.. Sometime they get this and sometimes they dont. Mine scratch all the time just by occasinal bugs jumping on or off or from dander or dry skin.... Hope this helps kaila..Well most chickens DO have mites.  Some of them you might find around the tail end and some you will just find if you part the feathers on the back of the bird.  You can get some spray from your vet which is quite effective.  Basically there are two types, black mites and red mites.You hen house needs a really good clean out, put on your oldest clothes, cover your hear and give the whole place a covering of creosote getting into all the corners, THIS WILL KILL EVERYTHING!   Then burn all the old bedding and put fresh straw in and having sprayed your birds too that should keep them away for a little while.  Make sure that the perches they have to roost on a night time are also well creosoted as many birds also get Scaley leg, which is a mite that gets onto the legs and makes them look like scales.
This will then pass from one bird to another.  it is treatable but vets bill are always best to be avoided if at all possible.
it is also good to worm you bird at least once a year too especially if they are living in an enclosed area which tends to get stale.  The ground needs turning weekly at least.
Hope this is helpful.