It wasn't hard to spot the plants. I rounded a slight bend in the road, which followed a small creek, and saw dozens of typical red-flowered plants. Not far behind were a dozen or so magnificent white-form plants, and they fairly glowed in their shady haunts. Above, one of the white plants grows side by side with a typically colored form for ease of comparison.
Well, there were indeed some hummingbirds about, but they only occasionally visited the Cardinal-flowers and never did come into the white-flowered plants which I set up on. They seemed far more smitten with the numerous Spotted Jewelweed, Impatiens capensis, another wildflower which is coveted by the little birds. In fact, there was a huge patch of the stuff right behind my position, and a male Ruby-throat was guarding it fiercely. He'd drop down and feed at the flowers for a few minutes, then zoom back up to a conspicuous perch overlooking his kingdom, only 15 feet behind my head. Any other hummers that came near were promptly driven away.
As the air warmed, the swallowtails became active and eventually stole the show. At times, fifty or more were mobbing the Cardinal-flowers and three or four often sparred over the same plant, as in the photo above. These big butterflies quickly became my focus.
PHOTOGRAPHIC NOTE: Nearly all of these photos were made with the Canon 5D IV and Canon's superb 500mm f/4 II telephoto lens, mounted on a tripod. Big butterflies such as these really transcend macrophotography, and are easier to shoot from afar with a telephoto. This allows the photographer to remain far enough back to be completely unimportant to the insects, which will operate free of disturbance and as they naturally would. Most any lens of 300mm and up should work very well for swallowtail photography.
Indeed, the flowers appear tailor-made for swallowtail access. The three lower petals hang down, offering a convenient perch for butterflies wishing to plumb the nectaries at the base of the long corolla tube. This arrangement puts the head of the insect in close proximity to the flower's reproductive parts, which are the grayish-white extensions at the top of each flower. When a flower is young, the reproductive extension is a brush or beard-like spur that contains the anthers, which hold the pollen. As the flower matures, the female stigma becomes exserted from the corolla tube - a stigma can be seen protruding from the flower directly opposite the butterfly.
So, the end game for the plant is to have an animal vector move pollen from anthers to stigma. As colonies of Cardinal-flowers, and even individual plants, will have a combination of flowers with exposed stamens/anthers and stigmas at any given time, flower-hugging butterflies would certainly seem capable of accomplishing this task.