The hackberry emperor is a member of the brushfoot family that has a range which stretches into the southern half of Minnesota. The hackberry emperor caterpillar only eats the leaves of the hackberry tree, or possibly elm leaves, so they are only found in areas where these trees grow.
There are typically two broods of hackberry emperor per year. The first brood hatches should be hatching soon, usually the end of June and beginning of July. The second brood usually hatches near the end of August. The second brood will over winter in the larval form. You don't usually see these butterflies on flowers because they do not drink nectar, instead they are attracted to tree sap, bad fruit, and animal waste.