It's Monarch season:
Wisconsin and other Midwest states are right in the middle of the monarch migration trail or flyway. During spring and summer, the butterflies travel north toward Canada to repopulate. Now they are preparing to migrate south for the winter.
...[M]onarch butterflies have a four-generation migration strategy. Right now, people in Wisconsin and the Midwest are seeing the fourth generation of butterflies. The first generation starts in Mexico, as monarch butterflies stay in the mountains of Mexico all winter. When they begin to migrate north during the spring they start to reproduce and repopulate, these are the second and third generations.
The butterflies being seen now are the offspring of the butterflies that migrated from Mexico last winter. Monarchs spend most of the summer in the northern part of the United States and southern Canada.
h/t Capper; Open Thread below...