Cow, horse, dog, and chicken manure are all great nurseries for fly larva. The flies lay their eggs on the fresh poop and the eggs rest there until either you or Maw Nature adds water.well folks its been 5 years since you all posted about flies. I opened my door this morning and 250 flies came in. (i may be eggzagerating) a bit. I'm thinking they reproduce in the chicken poo, don't you?....