Propertius duskywing (Erynnis propertius)

Physical description

The Propertius duskywing is the largest of our duskywing species with a wingspan of up to one and three-quarters inches. The upperside of the wings are brownish with fore wings more mottled gray; the underside of the hind wings has well-defined spots. The sexes are dimorphic, the female wings are lighter and spots on both wings are larger. Sexual dimorphism means that males and females have different physical characteristics, such as color and size.

Ecology and life history

The Propertius duskywing is an obligate of Garry oak (Quercus garryana), meaning it is dependent on this oak for its survival. This oak serves as the butterfly’s hostplant where developing caterpillars (larvae) feed on oak leaves for nourishment. The primary nectar plant for this species is common camas (Camassia quamash).

The Propertius duskywing inhabits low-elevation (up to 2000 feet), open-canopied, oak woodlands and savannah. Oak woodlands are rare, patchily distributed, and declining in western Washington. Research is needed to determine the specific Garry oak understory requirements of the species’ larvae for overwintering, and by pupae for their development. Leaf litter is important to protect the larvae during hibernation. In the spring pupation occurs in a vague cocoon.

These skippers complete a single life cycle annually (univoltine). They are sedentary butterflies and do not migrate; instead, the species inhabits sites year-round (as egg, larva, pupa and adult), typically moving within only a few hundred meters of their natal locations.

Adults emerge from their chrysalids (pupae) during April through May. Males begin emergence first, followed by females; late-season individuals are primarily or solely females. Weather influences butterfly emergence and the flight period duration, with wet or cold conditions delaying emergence. 

Both males and females feed by using their long proboscis to sip floral nectar.

Male skippers seek mates by perching on low vegetation and then darting out to inspect passing butterflies. Males that detect females commence courtship behavior; when males detect another male they engage in a territory defense behavior of tight, upward spiraling flight.

Females search for egg-laying sites by slowly flying and hovering just above hostplant vegetation and then depositing single eggs.

Skipper larvae conceal themselves in silken shelters and primarily feed at night. Propertius duskywings are members of the Pyrginae subfamily, whose larvae construct large cocoons in folded oak leaves, which drop to the ground over the winter, where pupation occurs in early spring. The Propertius duskywing overwinter as larvae.

Geographic range

Overall, the range of the Propertius duskywing is aligned with its oak host distribution in southwest British Columbia, Canada; the south and north Puget Sound and eastern slope of the Cascade mountains in Washington; western Oregon; and south to northwest California. In Washington, the butterfly occurs in a few small, isolated populations. Occurrence has been documented in Mason, San Juan, Skamania, and Thurston counties.

For a map of range-wide distribution and conservation status of the Propertius duskywing, check out NatureServe Explorer.