Every year when warm weather persists into the late fall, various observers here in the northeast report Clouded Sulpurs instead of or in addition to the expected Orange Sulphur. Back in the mild fall of 1999 I did some research on this subject. According to a couple of people at the New York City Butterfly Club, the Orange Sulphur has a cold weather form called ariadne. James A. Scott (1986) calls this form vernalis. It 's characterized by fine black speckling on the hind underwing which, mixed with the yellow ground color, gives it a somewhat greenish look. Scott citing W. Watt writes "the darker unh helps warm them when they bask laterally in cool spring days". There are also dark markings (one person called them chevron shaped) on the hind wing rim (if I interpreted that correctly). I was fortunate enough to have an opportunity to photograph one on Sunday. In the top picture, the flush in the upperwing color tends slightly toward that of Orange Sulphur. When I saw it (and 2 others) in flight, however, it didn't show conspicuous orange flushing, but the color was not light enough for Clouded Sulphur either. It is also said to be smaller than typical forms, but I can't say that I noticed that. That might be more apparent in early spring. Click on the images to download larger versions (the bottom one will be a non-flash version) and compare to a summer form.

Our concept of why Orange Sulphurs make these late season appearances is that they are not originally native to these northern latitudes, having evolved in areas where such emergences do not result in genetic dead ends. Scott writes "because of its recent spread north, diapause is poorly adapted there, allowing ill-fated emergence of some adults in warm periods in late fall". This in fact may be a common denominator for other species that are seen at this time. Monarchs, Buckeyes, and American Ladies are all species that annually move in from the south.