Large numbers of Painted Ladies have been emerging in central and western Iowa and in the Omaha, Nebraska area (and most likely elsewhere in Iowa and the upper Midwest). In central Iowa, the numbers of adult butterflies were relatively low up to and on June 27. However, large numbers of mature 5th-instar larvae were observed feeding on thistles near Dawson, Iowa on June 17, and larvae were also reaching pest levels in some Iowa soybean fields - suggesting a huge irruption was about to occur. Then, beginning on June 29, the next generation suddenly emerged in huge swarms, with hundreds along a typical mile of Iowa roadside. Painted Ladies had not yet emerged in northeast Iowa as of July 3, but larvae were present. suggesting that the irruption there is just a matter of time, and is likely to be accompanied by other butterflies arriving from more southerly regions.
These are the abundant offspring of a previous generation of butterflies that arrived in Iowa this spring from the western U.S., perhaps from regions such as Colorado or New Mexico, where large outbreaks had occurred from early April to mid-May. The butterflies emerging now are perhaps the fourth or fifth generation since the first ones appeared in the southwestern U.S. and northwestern Mexico late last winter.