I don't know that much about chickens, but, maggots are a good thing on people! I was a Army Aviator, H60 Blackhawk and UH1 Huey. The training I had included emergency survival medicine. If we had a wound that showed signs of infection, but we had no meds, the Army said the flys will make maggots and the maggots will clean the wound but will not eat living flesh. Only the dead flesh and puss! Then drop off! Years latter I saw the same thing on the movie "Gladiator" with Russel Crow.
But You don't want the Bott Fly! Thats another problem you don't want to know about!