Questions about a wierd flying bug.?

Okay so yesterday I saw this wierd bug with a regular fly, I don't know if they were mating or if the thing on top of it was sucking it's blood. The bug on top of the fly, was long, furry, and fatter then a mosquito, and had a long stinger on it's "butt" It also had a long needle looking thing out of it's mouth and it penetrated the regular fly, when I looked at it closely, so it looked like it was eating the fly. But I have seen these bugs before, but I have no idea what it is. I thought maybe a crane fly, but do crane flys eat regular flies, it was either eating it or mating with it, but more likely it was eating it when I saw that needle out of it's mouth. So, can anyone tell me what bug it was that eats regular flies, that is bigger and fatter and furrier than a mosquito, but definetely not a mosquito, it's bigger than a mosquito. I'm just curious.