I've got four adult hens and one chick in a city back yard. They've got a coop and run and during most days range the fenced back yard. I keep the run clean and lay down plenty of food-grade DE. However, there's been a dramatic increase in houseflies in our yard/neighbors' yards since we began keeping these birds last year. Every time you open the door, you get flies in the house..when you sit outside to picnic, flies. Is this normal? Is there anything I can do? The flies are such a pain I'm actually thinking of getting rid of all the chickens.