Many of my birding friends show an interest in butterflies during the slow, hot months of summer. And since so many birders are proficient at sorting out look-a-like shorebirds and confusing fall warblers, certainly they can learn the few anomalies in butterflies.
Only a few species of butterflies show significant dimorphism: the male and female look markedly different. One species, the Tiger Swallowtail, has two different female forms. These are both female Tiger swallowtails pictured in the photo below.
The commonly recognized "tiger" form of the female on the left is only slightly different than the male tiger swallowtail. She sports a bit more blue at the base of her hindwing.
However, the black-form female tiger swallowtails can be a real poser. Maybe we need to talk about those confusing "black" butterflies? This black-form female still has a blue band at the hindwing, and if you see her against the light- you can actually see these faintest of stripes!! That is a sure bet you are looking at a dark-phase female tiger.
Suprise! Now we have added a male to the mix - a male Spicebush Swallowtail. He has just joined the ladies for a drink (of nectar). He is also a dark butterfly similar in size to the tigers, yet there are no see-through wing stripes. We can easily assess this a male, as his hindwing color is green. A female Spicebush would have a blue coloration.
Tigers can routinely be found nectaring on brightly colored flowers, such as Purple Coneflower and Ironweed. But this photo from Adams county was the first time I have seen them nectaring on the incredibly fragrant Virgin Bower, Clematis virginiana. I have one in my landscape but I rarely see it utilized by butterflies. I plan to take a much closer look to see if mine is actually a hybrid, that may not be producing a sweet smell or nectar like Ohio's native plant.
Blue Jay Barrens posted a wonderful article on Virgin Bower and I encourage you to tap on the link and visit his sight for for more information about this wonderful native plant.