Butterfly photography requires a certain amount of stealth. I use a single-focal length macro lens–105 mm, and slowly get as close to the butterfly as I can. In bright sun, I use an aperture of f/16 and a shutter speed of 1/250 sec, at ASA 100. Here is a photo I took of a pearl crescent with those settings.
Ideally you have the sun to your back. But when you are stalking the butterflies, that does not always happen. It can help to use a little fill flash–keeping it simple, I use the pop-up flash on my camera. That changes the aperture to f/22 and the shutter speed to 1/200. I always use the manual settings so I have complete control.
If I used more flash, or if the background were farther away, the background would go dark. With this photo, that is not really an issue.
A little bit of flash really helps this photograph.
I found a pair of little yellows, mating while hanging upside-down under a leaf. Here is what the photo looks like using the fill flash.
The photo is clear, you can easily see details of the scales and the eyes, and even little hairs on the leaves.
Without the flash you lose some of the sharpness and detail, but you get more of a sense that the butterflies are underneath the leaf. In this instance, the natural light photo is much better.
At least, that is the way I see it.