I agree with Ian's suggestion that you look at something longer to get more working distance between the lens and your subject. I tried a an old 55mm and 60mm Nikon macro lens with my APS sensor D70 and D300, and while they were OK for static subjects, the working distance was just too close for bugs.
I currently have the 105mm VR macro, and the working distance is quite a bit better - but I'd love one of the 200mm macros for even more.
The nikon zoom macro lens was handy for changing the framing without having to move the camera - but there was a lot of glass in there and it was prone to lens flare. (also, if memory serves, you had to add a close up lens to get to 1:1).
If you're after a butterfly lens that only goes down to 1:4 or thereabouts (so not a true macro) then the Nikon 80-400VR zoom works very nicely - you get a very large working distance and it makes a nice wildlife lens too.
Also worth looking at in the butterfly lens category are the later nikon 500mmf8 MF mirror lens (the later version focuses falrly close, the older one doesn't so doesn't work for this) and the adaptall-2 tamron 500mm f8 MF mirror lens - again, this has a good close focus.