Lady bugs are one of the best aphid controls but they are not always in the adult form.
This shows ladybugs that were present in my own yard in two stages we don't think are ladybugs.
They are never a threat to the eggs, cats, or adult butterflies; but they do feed on the aphids.

Hover Fly larva also chomp down on aphids. Pretty gruesome to watch. They nab an aphid and suck it dry!!! This is a very old photo - sorry for the quality...but you get the picture!

Great picture, old or not. Thanks Cat.