A. idalia range maps: Historic and current

If you were to just travel back in time 70+ years ago, the Regal Fritillary would be an abundant and widespread butterfly across our nation's grasslands and into central Canada. They were even found in urban areas such as Chicago and Central Park in NYC. At this time both the western occidentalis subspecies and the eastern idalia subspecies had very robust populations. The map above is not separated by subspecies because it is likely there would've been crossover in states like Michigan, Indiana, and Ohio. After 1950, however, there is a noticeable decline for both subspecies (but especially the eastern) that appears to get worse every decade.

In post 2020 North America, we see a much different situation. The eastern idalia populations were almost completely wiped out from a variety of factors including the urban sprawl and loss of habitat. The only known population resides on the Airforce base Fort Indiantown Gap in eastern Pennsylvania. While the western subspecies is still numerous in some areas, the Fritillaries are moving into more secluded areas and shrinking their range. This map pins some of the areas where major populations still exist. 

Every state population varies. The table below lists the general background information for each state included in the map range. See where your state ranks. 

State/ region Details
Great Plains States (ND, SD, NE, KS, OK) The Great Plains certainly hold the strongest Regal populations in the country. Most well-maintained tall-grass and mixed-grass prairies contain solid western populations. With the exception of Oklahoma, Regals are found in all 4 corners of the Great Plains. Regals only seem to be found irreguarly in the northern prairies of Oklahoma.
Iowa and northern Missouri The Western Midwest still has many solid populations of western Regals. They become more abundant in IA and MO as you move away from the Mississppi. Regals historically have been restricted to northern Missouri as the Ozark region is not their preferred habitat. They have only receded in MO.
Minnesota Occidentalis excels in the sprawling prairies of southern and central MN as they are able to tolerate the extreme temperatures. They have even been introduced county parks around the Twin Cities.
Illinois Illinois has many various populations located around the northern prairies of the Driftless areas and the sand counties near Springfield and Kankakee.
Wisconsin Wisconsin used to have Regals throughout the south and central part of the state. Now they only have 3 main populations in Portage county, Fort McCoy in Monroe, and northern Grant County. They are likely to be around for some time as they have robust populations. Some adults also seem to wander to other parks in the Driftless region.
Indiana Indiana lost almost all of its Regal presence. Only one main population is known in the Kanakee Sands on the Illinois border and it is the eastern-most site of occidentalis.
Montana and Colorado Montana and Colorado are the western-most extents of the range. Regals are only very rarely found in the far-eastern prairies MT. Colorado's Pawnsee National Grasslands still have a strong colony found each year.
Eastern Pennsylvania Like Indiana, Pennsylvania is near the brink of Regal expiration. The Fort Indiantown Gap base contains the last known population of eastern idalia. Luckily this site is heavily protected and while local, these butterflies have a robust colony.