Old World Swallowtail (Papilio machaon): These are among the first swallowtails we see in the spring, flying from late April to early July on open hilltops and in mountain meadows. They are very easy to mistake for the Anise Swallowtail (Papilio zelicaon). To tell the 2 species apart, you need to focus on the “eyespot” on the hindwing. The black eyespot on the Old World touches the inner edge of the hindwing. On the Anise, the black spot is centered or circled with orange. Definitely tough to see unless you get a photo. Photo by Glenn Marangelo on 5/20/18 near Charlo, MT.