These little guys appear in our lab fairly frequently, and are really annoying. There are probably around 30 of them flying around our lab right now. Dr. Peter Bryant, whose office is down the hall, suggested that they might be some kind of parasitic fly feeding on the Drosophila carcasses or something, but he couldn't get any more specific and suggested we send some pics to you guys. We would love to figure out where they're coming from so we can get rid of them. They're getting into our tubes, laying eggs, and generally wreaking havoc. Any help you could give would be great, but (mostly out of curiosity) I'd be really interested in knowing their precise scientific name.