All chicken have mites, which is why they dust themselves but the warm weather multiplies them. These mites feed off the chickens blood supply, making your chickens anaemic and if left untreated die.
The total kill ready to use solution containing pemethrin 0.23%, tetramthrin 0.023%, benzalkonium chloride even if sprayed directly onto the mites does not kill them. I have found that ant killer spray kills red mites and other crawling insects dead and stops them coming back.
I remove all bedding and shut the chicken out of the house while I spray and until the house is dry. During this summer months I have only had to do this twice.
I also dust my chickens every 6 weeks with total mite kill powder which contains diatomaceous earth, and use a mite recovery tonic in the water post any infestations.