Western Tiger Swallowtail . This yellow and black tiger swallowtail ranges from the Rocky Mountains to the Pacific coast, and is at home in many habitats, including suburban gardens and parks. For those of us who grew up in the suburbs, this was the big yellow swallowtail that frequented our neighborhoods. One reason it is at home in so many places is that it can use several popular trees as the larval food plant: ash trees and sycamores seem to be preferred, but willows, cottonwoods, poplar, and alders are also known hosts. Outside the cities, these trees grow where there is water, and that is where rutulus may be found. Hilltopping is not in their repertoire, though it certainly is for the closely-related pale swallowtail.