This butterfly was spotted and photographed by Dan Sonnenberg on a farm in central Wisconsin this past weekend. The image was shared with other members of the Southern Wisconsin Butterfly Association, none of whom had ever seen such a coloration pattern.
After much pondering and web-searching, the current opinion is that it is an aberrant form of a Pearl Crescent. For comparison, here is a "normal" Pearl Crescent I photographed a couple years ago:
The size and wing shape (and time of year, and location) are similar, but the coloration is dramatically different in the mystery butterfly. Mike Reese, president of SWBA, found this comparison photo at Bug Guide -
- of a butterfly presumptively identified as an aberrant Pearl Crescent.
Dan was able to capture a view of the underside of the mystery butterfly's wing -
- which is at least marginally Pearl Crescent-ish. (Here's one from my files)
The photos of the "mystery butterfly" have been submitted to the North American Butterfly Association, which will publish the images and solicit professional opinions.
If any readers here have suggestions or know of images of similar butterflies, please don't hesitate to append a comment.