Feces that contained residues of digested dairy feed supplements were offered as ovipositional substrates to cagedMusca sorbensWiedemann to determine preference. Results showed preference for residues of digested ground corn. Ovipositional preference for residues of digested ground corn over those from coarser rolled corn suggested a relationship between surface areas exposed to digestive fluids and intensity of ovipositional preference. Feces of cows that were fed complete rations formulated without corn were ovipositionally unattractive to cagedM. sorbens.