Butterflies found in the Pacific Northwest include Spicebush Swallowtail, Painted Lady, Cabbage White and Red Admiral. Migratory Monarch butterflies are found throughout most of the United States. They migrate north in the spring and can be found in Washington State, mainly east of the Cascades where milkweed is abundant. The Washington Butterfly Association publishes a list of butterflies found in the Puget Sound Region and their food plants.

Butterflies are important pollinators but their populations are in decline, mainly due to habitat loss. Butterflies and caterpillars are also important food sources for other pollinators, such as birds. The Xerces Society (named for the now extinct California butterfly Xerces Blue) provides education and guidance on butterfly conservation worldwide.