Help ID this insect

I don't have any pictures... But I will do my best to describe it. It is in the Diptera order. It has an orange body (but is not drosophila it is much larger). Its wings have black stripes on them, almost in an X pattern. Large eyes. I am working in northern IL, but originally from MO, and I have seen them all over. Currently they have been mating on Asclepias tuberous on our nursery lot. I forgot my insect ID book at home and wont be back for a while. Please help!