Flying bugs around my cannabis plants, why?

I have two beautiful cannabis plants, they are still young, one is about 8 inches tall, the other not even close to that big. I checked on them one day, and i found myself looking at a bug, it almost looks like a mosquito. It has a peachy color to it. I've been killing them. I was wondering if these bugs are harmful to my babies, and why exactly are they taking a liking to them.