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.

There were several first-of-season Painted Lady observations reported through the CarolinaLeps newsgroup in early to mid-July. The first was observed on July 9 in Winston-Salem, North Carolina by Gene Schepker. Two Painted Ladies, along with 7 American Ladies, were observed by Harry LeGrand on July 10 in North Carolina State University farm fields south of Raleigh. Another first-of-season Painted Lady was observed on July 14 by Carolyn Seaton in Lancaster County, South Carolina. Painted Ladies typically tend to first arrive in the Carolinas in early to mid-summer, and are often considered noteworthy when they are spotted there.

One month after the last Painted Lady irruption in the final days of June, another generation, perhaps even larger, suddenly emerged in central Iowa on July 29 and 30. I went out on a survey and collecting trip in Story and Boone Counties on the 30th, and found hundreds of fresh butterflies milling around and flying across Highway 17 and other local roads between Boone and Luther. There was also a large emergence between Polk City and Ankeny, with perhaps 200 along a stretch of highway between these towns. Hundreds were also observed along Interstate 80 in eastern Polk, Jasper, and Poweshiek Counties, but there were very few along I-80 farther east in Iowa and Johnson Counties, suggesting a somewhat localized irruption so far. Many of the butterflies seen along I-80 were flying north, but others were flying in various different directions.

Farmers in our area continue to have problems with "thistle caterpillars" feeding on their soybeans. While I was out monitoring yesterday, I met one grower who said that he had had to spend $30,000 this year for spraying his soybean fields for Painted Lady caterpillars. He was also disappointed to hear from me that there could be yet another generation of larvae before a final brood of butterflies emerges in early September to fly south.

This irruption began earlier in the month in the Omaha, Nebraska area, sometime between July 18 and July 23, as reported by @langabee from weekly surveys there. From those reports, I was anticipating another irruption in central Iowa, while wondering why it wasn't happening here for another week to 10 days after beginning in eastern Nebraska. Perhaps some observers in western Iowa can fill in the blanks here.