While it is not always easy to tell the caterpillars of swallowtails apart, we believe this is a Western Tiger Swallowtail (Papilio rutulus). They can be found in a wide range of habitats, including riparian woodlands, canyon streams, wet montane meadows, wooded suburbs, and gardens. Younger stages of the caterpillars resemble bird droppings. Older caterpillars range in color from green to the purple / brown color pictured here and sport eyespots with a separate, yellow spot inside each. This caterpillar will soon transform into a chrysalis to wait out the winter. The bright yellow adult butterflies can be found flying from June into July. Take a peek at the life cycle.
Photo by Kathy McEldery on 9/3/20 in Plains, MT.