Most of the fly's body liquids are yellow or yellowish but another man on YA answered a similar question by saying that the red blood is from a fly's eyes. I have also killed flies that leaked red and / or yellow.

colorless, pale yellow or green, since insect don't have hemoglobin in their blood (what gives our blood a red color)

It must have been a mosquito that had recently stung someone, or the red color could have been something that was in the digestive system of the insect, or, and most likely, it was a red colored pigment present in the fly's eyes

Usually when I swat flies there's this gross yellow smear, but today I swatted one that was on my ceiling and there was a spot of bright red where the body had been (it fell a few seconds later) this is grossing me out and I'm wondering why this fly was different..? It definitely WAS a FLY by the way, I got a good look at it.

I've tried looking this up, and there aren't many answers online but most of them are saying flies' blood is colorless..?! Surely that can't be right!

Sorry I know this is gross but I'm really curious about this!

Thanks in advance =)