More face flies,Musca autumnalis DeGeer, are found on cows lying down than standing and these numbers increase further when animals are in the shade. There are large differences between individual animals, apparently influenced largely by color and animal activity. Fly activity is influenced most by incident light, provided temperatures are above 60–65°F. In studies of fly dispersal, marked flies were recovered at distances up to 1500 m within 72 hours after release. It is probable that they move much farther.