Propertius Duskywing

The distribution of E. propertius aligned with its host, Garry oak, primarily in southwestern British Columbia, Canada; the southern and northern Puget Sound and the eastern slopes of the Cascade Mountains in Washington; western Oregon; and northwestern California. In Washington, E. propertius exists only in small, isolated populations. It has also been observed in Mason County, San Juan County, Scamaria County, and Thurston County. E. propertius is frequently found in oak-dominated habitats, such as open woodlands, forest edges, and savanna habitats that contain Garry oak. It is closely associated with Quercus garryana ecosystems in British Colombia, which are naturally fragmented and have limited distribution. The scattered presence of these habitats has resulted in limited local population structure and interpopulation dispersal. In the southern part of its range, E. propertius feeds on other oak species.

E. propertius go through one life cycle per year. Unlike some other butterfly species that migrate, E. propertius usually stay within a hundred meters of their birthplace. These butterflies stay in the same site all year, whether they are eggs, larvae, pupae, or adult butterflies. Larvae feed on the leaves of Garry oaks. They conceal themselves in silken nests and primarily forage at night. Their large cocoons made of folded oak leaves fall to the ground during winter, where they overwinter as sixth instar caterpillars. The larvae pupate in early spring in the oak leaf nest. Adult E. propertius typically emerge from the pupae during April and May. The males come out first, then the females. Late-season individuals are primarily female.