This photo provides a handy size comparison. The large yellow butterfly in the background is a Cloudless Sulphur, and the smaller butterfly (front right) is an Orange Sulphur. Cloudless Sulphurs are easily twice as large as our Orange and Clouded Sulphurs. These two butterflies were puddling side by side in damp mud at Cox Arboretum.
Cloudless Sulphur nectaring at a thistle flower. Cloudless Sulphurs are noticeably different from our more common Orange and Clouded Sulphurs. They are much larger, and their wings sometimes have a faint hint of lime green. Also, Cloudless Sulphurs have a more powerful flight than Orange and Clouded Sulphurs.
I love how this photo of a Cloudless Sulphur turned out. The butterfly was nectaring on a sunflower on the Cox Arboretum prairie. There were plenty of other plants in the background, but my camera managed to blur the background, leaving the butterfly and sunflower nice and sharp.
This Cloudless Sulphur is nectaring on a royal catchfly flower, another native prairie plant. Cloudless Sulphurs will readily investigate any red blossoms. They are much like Ruby-throated Hummingbirds in that regard!
This Cloudless Sulphur is nectaring on blazing star, a native prairie plant. Cloudless Sulphurs are usually found in open habitat like prairies and meadows. Their host plants are wild senna and partridge peas. You will have your best luck finding Cloudless Sulphurs in locations where these plants are common. Cox Arboretum, the Caesar Creek Wildlife Area, and the Meadow Ridge area of Elk Creek MetroPark are all good locations.
This is another female. Cloudless Sulphurs are stray visitors from the south. They can't overwinter in Ohio, so their numbers vary from year to year. Cloudless Sulphurs were formerly considered rare in Ohio, but with warmer weather, they have been expanding their presence in the state. In most recent years, they have been fairly common in southwestern Ohio.
This is a female Cloudless Sulphur. Females have white "leaf mold" spots on their wings, unlike the males which are mostly solid yellow (see above).
Here is a Cloudless Sulphur on a Cardinal Flower, another red flower. I have seen Cloudless Sulphurs from late May through the end of October in our area (weather permitting), but they are most numerous in late summer and fall.
Last but not least, here we have a Cloudless Sulphur with its wings spread. These butterflies never rest with their wings spread. I only got this photo because this male was fluttering around a newly emerged female. You can see part of her chrysalis in the background. Cloudless Sulphur males have unmarked yellow wings. (Females might have a very thin black border.) Orange and Clouded Sulphurs, by contrast, have a thick dark border on the dorsal surface of their wings.