Valley silverspot (Argynnis zerene bremnerii)

Physical description

The valley silverspot is in the genus Argynni (greater fritillaries). It has distinctive black line and dot patterning on its bright orange upperside, and a heavily-patterned underside with silvery orbs. Wingspan is up to 2.5 inches. Fritillary larvae are generally dark with many bristled spines.

Ecology and life history

The valley silverspot is restricted to native grasslands in western Washington, primarily montane meadows in the northeastern Olympic Mountains, and low-elevation, short-stature grasslands in the south Puget Sound region. In a two-year study of valley silverspot habitat and nectar use on two south Puget Sound prairies, early blue violet was identified as a larval host, and two plants were selected for adult nectar sources (showy fleabane, [Erigeron speciosus] and Canada thistle [C. arvense]). There have been no hostplant or habitat studies in Olympic Mountain populations.

Like other greater fritillaries, the valley silverspot 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). Adults emerge from their chrysalids (pupae) during species-specific time periods; typically early-to-late summer. 

Males begin emergence first, followed by females; late season individuals are primarily or solely females. Weather influences butterfly emergence and flight period duration, with wet or cold conditions potentially delaying emergence.

Male fritillaries seek mates using rapid patrolling and searching flight behavior. Females search for egg-laying sites by slowly flying and hovering above hostplants and then landing and crawling to inspect vegetation before depositing eggs singly.

Both males and females feed by using their long proboscis to sip floral nectar. Research on other Argynni species suggests that nectar availability affects the number of eggs laid by females.

These species depend on violets (genus Viola) for their hostplants. Argynni fritillaries lay eggs late in the summer. A tiny larva hatches within a few weeks and seeks shelter to overwinter, but does not feed until the following spring. Larvae feed nocturnally on their hostplant; this characteristic, along with bristled spines on their dark body and a gland that secretes defensive chemicals, protects them from predators.

Geographic range

The distribution of the valley silverspot is limited in part by their dependence on rare habitat types. Their distribution and abundance in Washington is characterized by low numbers of small isolated populations. Declines in both the number and size of populations have been documented for this species.

Surveys have been conducted to determine the current distribution of the valley silverspot in the south Puget Sound region. Little is known of the current status and distribution of the species in other portions of their range within the state.

The species in Washington has been detected in the following counties: Clallam, Clark, Cowlitz, Jefferson, Lewis, Pierce, and Thurston.