Butterflies like the Monarch have always been one of my favorite parts of the prairie.
MonarchWatch has some interesting prairie-as-habitat information on their web site and have even started a blog. For example, in "Status Report on the Monarch Butterfly (Danaus plexippus) in Canada" by Crolla and Lafontaine they state:
In the last 150 years there has been a major shift in the North American distribution of the eastern population of the Monarch (see Brower 1995). Until the 1880’s, the prairie region of central North America appears to have been the main breeding area of the eastern Monarch population. The native prairie flora includes about 22 species of habitat-specific milkweeds (Asclepias), many of which can serve as larval hostplants, and an abundance of flowering plants that provide a diverse array of nectar resources for adult Monarchs.
In the latter half of the nineteenth century, plowing destroyed 433 million acres of the midwestern prairie, and by 1910 most of the native prairie had been converted to crop land (Brower 1995). Concurrent to this widespread destruction of the prairie flora, the deciduous forests of eastern North America were being cleared on a vast scale. Most of the deciduous forest in the eastern United States had been cleared by 1860, and from 1860 to 1890 an additional 50 million acres of forest in the Great Lakes region was cut (Brower 1995). One result of the opening of the eastern deciduous forest was a rapid and widespread proliferation of the weedy Common Milkweed (Asclepias syriaca) in cleared lands across the northeast. The destruction of the native prairie flora of the midwest (with its associated milkweeds), and the concurrent rapid spread and increase in abundance of Common Milkweed in the northeast, appears to have resulted in a major shift in the main breeding range of the eastern population of the Monarch, from the Great Plains to northeastern North America This expansion into the northeast was characterized by a shift from utilization of a variety of prairie milkweeds as larval hostplants, to the utilization of Common Milkweed as the primary larval host of the eastern population of the Monarch in North America.