A toast and tip of the sunshading straw hat to Teddi today. Cheers! Her photographs that accompany this post are perfectly beautiful AND they afford an opportunity to talk Swallowtails and Monarchs. I’d intended to showcase hummingbirds all week (since they’ve been spellbinding me daily with sightings in the morning room flowerbed, the “ice garden”, and the wildflower garden), but the draft remains a draft. Brushed aside by Teddi’s sun-soaked snapshots on Friday afternoon, I’ve decided it’s more timely and relevant to address the question of what beautiful butterfly we are witnessing in these photographs. Is it a Monarch or a Swallowtail?
I’m leaning toward the latter, but the question arose with Teddi’s message.
Monarch enjoying newly renovated wildflower garden. — Teddi Rogers
Could I be mistaken? Of course, I often am. And so it struck me that I’m probably not alone. Perhaps others too might mistake the two Lepidoptera. As so often in these wildlife questions, I reached out to John Davis. At the time of publication I’m still awaiting his confirmation, and I will update this post once I hear back. (See update below.)
In the meantime, a bit of sleuthing… 
While both species are in the order Lepidoptera, swallowtails are members of the Papilioninae subfamily and Monarchs belong to Danainae. Like most swallowtail butterflies, Eastern Tiger Swallowtails have a black “tail” on each of their wings. (Source: The ArthroBlogger)
Papilio glaucus, the eastern tiger swallowtail, is a species of butterfly native to eastern North America. It is one of the most familiar butterflies in the eastern United States, ranging north to southern Ontario, Canada, and is common in many different habitats. It flies from spring until fall, during which it produces two to three broods. Adults feed on the nectar of many species of flowers, mostly from those of the families Apocynaceae, Asteraceae, and Fabaceae. P. glaucus has a wingspan measuring 7.9 to 14 cm (3.1 to 5.5 in). The male is yellow with four black “tiger stripes” on each forewing. Females may be either yellow or black, making them dimorphic. The yellow morph is similar to the male, but with a conspicuous band of blue spots along the hindwing, while the dark morph is almost completely black. (Source: Wikipedia)
The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. It is among the most familiar of North American butterflies and an iconic pollinator, although it is not an especially effective pollinator of milkweeds. Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (3.5–4.0 in). (Source: Wikipedia)
What say you? I’m feeling considerably more confident with the likelihood that this breathtakingly, beautiful butterfly is an eastern tiger swallowtail. Don’t hesitate to correct me!
In closing, thank you, Teddi, for these captures and for provoking the question. And, John, thank you for answering my endless questions. Our Rosslyn adventure is so much richer for both of your participation! Thank you.
Update
I received John’s update this evening. We certainly are fortunate to have a knowledgeable wildlife steward on the team (and a quick communicator to boot!)
Lovely Eastern (or Canadian?) Tiger Swallowtail! They seem to be doing well this year, unlike some other butterflies. — John Davis
So my hunch was well founded for a change. Thank you, John.
What do you think?