It's probably more a function of last year's high moisture levels than this year's dry ones that there are so many butterflies in Colorado.
On many of the trails I've hiked this summer, the quantity of butterflies is striking. Diversity is good too, as I've noticed at least five different species (there are probably more, but I'm not a trained lepidopterist).
To get the best butterfly photos, I found one needs to stand still near some flowers they appear to like, with your lens zoomed in to the longest focal length. When they land on nearby flowers, begin shooting like crazy. If they remain for a while, you can take the time to properly compose your image or wait for them to open their wings.
