Fruit flies like a high alcohol and sugar medium. House flies like dung and rotten meats as a medium. House flies will not thrive in fruit fly media. Safe food options are beef liver, powdered buttermilk, and sugar. Make you throw a small enough piece of liver to ensure that the maggots and flies eat it whole. For water, soak some aspen shavings and throw them in your culture. In a few days, you will have an unlimited source of house flies!