Look out for Red Admirals! Large numbers of these butterflies have been migrating northward across the upper Midwest and southern Ontario, Canada in the last few days in the wake of a strong flow of warm, moist air from the Gulf of Mexico. Some observers have also seen either Painted or American Ladies flying with them. This wave of butterflies has appeared over a wide area of the upper Midwest from northeastern Kansas to Minneapolis, central Iowa, and southwestern Wisconsin within a relatively short time, between April 6 and April 9, suggesting a sudden incursion from elsewhere. To further support this possibility, there has been one report of a steady stream of northbound Red Admirals and Painted Ladies throughout the day on April 8 in Polk County in central Iowa.
-- Royce Bitzer, April 10, 2017