I spotted these Red-Footed Cannibalflies in the garden when I saw the bottom one trying to escape. He(?) was firmly attached and wasn't going anywhere, so he eventually gave up and dangled. (Cue me yelling "Kevin! Kevin! Get the camera!" and him muttering "This is my life...")
The really amazing thing is that the top one had another, smaller robberfly, of a different species, and was eating it. It's mostly hidden by the flower there, you can sort of see the edge of an eye. Apparently in some robberflies, the males will bring an offering to the females, possibly to avoid being eaten, so that may be what happened here. She didn't seem to care that there was a male almost her size dangling off the back.
(I am starting to think I really do need to fork over the money for a good macro-lens. This was taken with my iPhone and I don't know if the camera shots will have come out, given how far away he had to stand to get the focus.)
There are a LOT of robberflies in my garden this year. I think we may have hit some kind of tipping point in insect population where it can now support large numbers of insect predators, because I don't remember ever seeing anything like this quantity before. We've always had dragonflies, but this is wild.