Photo courtesy of Leticia Shaddix.  

Giant Swallowtails at Fermilab may most often be found near the woods edges in August.  Although very common in the southern United States where the caterpillars may be pests on citrus trees, Giant Swallowtails tend to be rather scarce and local this far north, most likely associated with the larval foodplant, Prickly Ash, found in our woods. 

The yellow underside sometimes causes Giant Swallowtails to look yellow as they fly overhead.  This Giant Swallowtail was fluttering its wings continuously while at the Monarda (bee balm) flowers, as many swallowtails do while nectaring. 

This Giant Swallowtail emerged in captivity from a chrysalis that overwintered in the Fermilab woods.  More photos and information are linked here.