Along with the butterfly milkweed there was also fields of common milkweed (Asclepias syriaca) which was also attracting butterflies. I stopped alongside the road onto the berm so that I could walk into the field and take more butterfly pictures. Except as soon as TB opened her door, she looked down and said "Oh my God, it's full of poison ivy." I decided that it would be smarter just to stay in the mowed area and take pictures using the macro zoom.
Doing a little research on the milkweed plant, Wikipedia had this interesting observation:
Pollination in this genus is accomplished in an unusual manner. Pollen is grouped into complex structures called pollinia (or "pollen sacs"), rather than being individual grains or tetrads, as is typical for most plants. The feet or mouthparts of flower visiting insects such as bees, wasps and butterflies, slip into one of the five slits in each flower formed by adjacent anthers. The bases of the pollinia then mechanically attach to the insect, pulling a pair of pollen sacs free when the pollinator flies off. Pollination is effected by the reverse procedure in which one of the pollinia becomes trapped within the anther slit.
And I have a picture of the Grand Spangled Fritillary doing exactly that on the Butterfly Milkweed (if you look closely, you can see his proboscis in the flower).
I'm beginning to see that these common weeds are not quite as uninteresting as I had always thought.