Finally, today, another giant swallowtail, again at mid-day, again on my mother's beautiful buddleia (beloved of butterflies). And this big butterfly was indeed the Giant Swallowtail (Papilio cresphontes)
Food plants for the larvae of this butterfly include Common Hoptree (Ptelea trifoliata) and Prickly Ash (Xanthoxylum americanum). We have a couple of specimen plantings of Common Hoptree (aka Wafer Ash), a species at risk in the small range of Ontario where it occurs naturally (here's a range map). We are growing it outside of its range here--but so far, so good. In more southern regions the Giant Swallowtail larva feeds on citrus, and is known as the Orange Dog, not well-loved by citrus growers. The leaves of the hoptree are said to have a citrusy smell when crushed. (I'll have to go check when I'm done here.) The Prickly Ash is very "citrusy" in a number of ways. They both come by it honestly, being members of the Rue family (Rutaceae) along with oranges and lemons etc.