Food supply is critical and so is the physical environment they each need. Since the Front Range of Colorado is prone to high winds at certain times of the year, it is helpful to provide shelter from wind for butterflies. Using windbreaks or a sheltered area is a good start. It is also important to know that most butterflies have specific host plants on which they develop. Monarch butterfly caterpillars will only develop on milkweed.
Black swallowtails feed only on parsley, dill and related plants.
The food supply for adult butterflies usually consists of nectar, or sweet liquids, produced by flowers. Some types of flowers produce more nectar than others and even flower color can attract or deter butterflies. For example, as mentioned earlier, black swallowtail caterpillars will munch on dill, parsley, fennel, and carrot. So be careful where you plant these if you want them for your dining room table instead of for caterpillar food. The same applies to the European cabbage butterfly which likes broccoli, cabbage, and other members of the mustard family.