Thanks for the reply. I cleaned out the coop and drenced it all with a strong detergent spray. This seemed to kill most of them. I then sprayed all of the house with an insecticide which apparently kills or crawling insects - pethryin or something - . I burnt all their bedding. I then doused the chickens in red mite powder liberally and waited for the coop to dry before letting them back in. I visited them overnight and they seemed to be far less distressed than the previous night - I did see a few mites crawling around on them, they were still squatting on the floor rather than on their perches above . This mornng there were alot of dead mites all over the coop and the hens seemed more active. I think they actually looked better and their combs were redder but that might just be my imagination! Im going to repeat the whole process in 3 days and keep my fingers crossed. Any advice would be welcome