Two-tailed swallowtails are primarily on the wing in late spring and early summer in Montana. They’re the largest of all our western butterflies (spread specimens sometimes push 6 inches in wingspan), and unique among them, sporting two “tails” on the hindwings. Many of our yellow swallowtails can be commonly found out in the woods as well as in your backyard. Males patrol stream courses or city streets looking for receptive females. The caterpillars commonly feed on chokecherry and ornamental green ash in our area. Like many other swallowtails, the younger larvae resemble bird droppings and the older ones have a bright orange, odorous organ (osmetriums) that can be everted from behind the head when under threat. The two-tailed ranges across western North America down into Mexico.
Photo by: Jacquese Rasmussen on 6/15/21 in Dillon, MT