Long-legged Flies

For as much as I like watching life progress in the terrariums, it always wigs me out a little when I look in to find something flying around that wasn't there a day earlier.

Making a terrific buzzing noise, two of these critters were flying around the tank. One did a nose-dive straight into a millipede who reacted very negatively, thrashing about and running across the tank to escape the assault. My thoughts instantly thought I was dealing wasps, but after closer inspection, I determined the insects were simple flies.

Given their bright coloring and red eyes, I'm pretty convinced they are long-legged flies (Condylostylus {one of many potential species}). Like many insects that appear seemingly out of nowhere, I have no idea when I would have pulled in their eggs or larva. Likewise, the flies appear to have died off as quickly as they arrived, unless they have simply been hiding from me the past couple days (although I doubt the optimistic thought holds true).

As to why one dove on the millipede, and why the millipede reacted so negatively, I couldn't tell you. I don't think they could harm the thick-shelled insects; I'm guessing it was more just a random flight accident. And, at the time, perhaps the millipede was a freaked out as I was.