Although it looks a bit like a tug of war, I think that these two Red-footed Cannibalflies (Promachus rufipes) actually were mating when I spotted them on Friday at Huntley Meadows Park. (Don’t ask me any anatomical questions–I am not sure how it works for them.)
This photo was taken from a pretty good distance away with my 150-600mm lens and is a little soft, but I thought I’d post it today as an accompaniment to my earlier macro shot of what I think is a female Red-footed Cannibalfly.
© Michael Q. Powell. All rights reserved
Mike Powell 
I also have some pictures of matings of insects. At almost everyone of them, they are hanging like this. Trying to get off each other, but the genitals locked. I wonder why? (have an idea that it may be an adaptation to give sperm a little more time to go over to the female. Not sure though)
I tend to agree with your idea on why the mating insects stay locked together so long, though I must admit that I am not sure if that is what scientists would say.
hah ha.. yeah. must ask a professional.
Get a room, flies 😀
🙂