Recently we've seen lots of this small fly in our house in Michigan. They are smaller than regular houseflies and don't have the distinctive green/blue sheen that houseflies have. I assume they bite, because at least once I've killed one and it spewed red (which I assume was blood), although I haven't actually been bitten by one to my knowledge.

The fly is about 8mm in length. They tend to sit on walls or ceilings without flying a lot, and they're not difficult to kill, i.e., they don't immediately fly off when approached unlike a regular house fly.

Is it possibly a cluster fly?

Here are two images. The first image is a live fly, the second is dead which is why the wings aren't flat to the body.

fly 1 fly 2

  • $\begingroup$ Some insects have internal body fluid and organs that can appear reddish upon disruption of the exoskeleton (aka - squishing). I wouldn't be so quick to assume it's blood. $\endgroup$
    – MattDMo
    Commented Aug 17, 2022 at 1:05
  • $\begingroup$ @MattDMo Fair enough but then wouldn’t all of them behave the same way when crushed? I’ve killed quite a few and only one had that result. $\endgroup$
    – Alan Munn
    Commented Aug 17, 2022 at 1:13


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