Thanks guys and gals.
Baz - I always use flash for macro. Find the apertures are just too small for natural light only. Usually fill flash, so try to expose the background say 1 or 2 stops under, then flash to make up the difference on the subject. Means you end up with some background definition rather than those black backgrounds you see often.
Example of black background, full flash look
Example of nice fill flash with background colour
Because I was shooting pretty much straight down for these, the flash was always going to light the background grass no matter what.
Equipment was Canon 30D, MPE-65 lens, MT-24 EX twinlight flash. Camera settings were ISO400, f/11, 1/200 or 1/250 I think.