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Oregon Silverspot Butterfly
Speyeria zerene hippolyta

General Information

Official Status: Threatened, the Oregon silverspot butterfly is federally listed under the Endangered Species Act as threatened.

Date Listed: effective October 15,1980; Federal Register: 45 FR 44935 (pdf, 500 KB)

Critical Habitat: Critical habitat was designated at the time of listing, and includes the salt-spray meadow between Big Creek and Rock Creek, Lane County, Oregon. This includes those portions of Section 15 and of the south half of Section 10 which are west of a line parallel to, and 1,500 feet west of, the eastern section boundaries of Sections 10 and 15, T16S, R12W, Willamette meridian.

Recovery Plan: Oregon Silverspot Butterfly (Speyeria zerene hippolyta) Revised Recovery Plan (pdf, 1.0 MB), published August 2001.

Oregon Silverspot Butterfly, Photo Credit: USFWS File Photograph

Oregon Silverspot Butterfly

Photo Credit:USFWS File Photograph

arrow button Photo Gallery for the Oregon Silverspot Butterfly

Identifying Characteristics:

This is a medium-sized butterfly with a wingspan of approximately 5.5 cm (2.2 inches). The upper surfaces are golden brown with numerous black spots and lines. Wing undersides are brown, orange-brown, and tan with black lines and distinctive silver and black spots. Basal areas of the wings and body are covered with fine hairs. The Oregon silverspot is a member of the family of true fritillary, or silverspot butterflies, of which 13 species occur in North America. The species Speyeria zerene, sometimes known as the Zerene Fritillary, includes a number of subspecies, of which 8 occur in the Pacific Northwest and on the California coast.

The Oregon silverspot butterfly is similar in appearance to two other coastal subspecies of Speyeria zerene, the Behren’s silverspot butterfly (S. z. behrensii) and Myrtle’s silverspot butterfly (S. z. myrtleae), both of which are also federally listed. The Oregon silverspot differs from the Behren’s silverspot primarily by less dark basal suffusion on the upper sides of the wings and its relative smaller size. The Myrtle’s silverspot is larger in size than the Oregon silverspot. Both the Myrtle’s and Behren’s silverspot butterflies occur well to the south of the Oregon silverspot.

Current Geographic Range:

The historic range of Oregon silverspot butterfly extended along the Oregon and Washington coasts from Westport, Washington south to around Heceta Head in Oregon, and in a separate coastal area north of Crescent City in Del Norte County, California. At least 17 historic sites are known. The current known range is limited to five sites, including four in coastal Oregon in Lane and Tillamook counties, and one in Del Norte County, near Lake Earl. The butterfly’s presence at a six site, in Clatsop County, is uncertain due to a population decline.

Life History:

Females lay eggs in the debris and dried stems of the main larval food plant, the early blue violet (Viola adunca). This is a small, native, perennial herb with pale to deep violet flowers, which typically blooms in late spring to early summer, and dies back to the perennial rhizome during winter. Early blue violets occur widely in western North America, but within the Oregon silverspot range, are associated with coastal grasslands and, at one site, montane meadows.

Little is known about the biology of the caterpillars or pupae. Caterpillars (larvae) are dark-colored with many branching, sharp spines on their backs. Upon hatching, the larvae spin a silk pad upon which they pass the fall and winter in diapause (dormancy). Upon ending diapause in the spring, the larvae seek out the violet food plant. During the spring and early summer they pass through six instars (stages of development) before forming a pupa within a chamber of leaves that they draw together with silk. The adult butterflies emerge in about two weeks and live for approximately three weeks, during which time they feed on nectar and reproduce. Depending upon environmental conditions, the flight period ranges from about early July through early-September in California, and starts and ends about two weeks later in Oregon.

Oregon silverspot butterfly flight behavior is moderately erratic and swift, and flights usually occur by late morning when temperatures are above about 60 degrees Fahrenheit. Adults may feed on nectar as long as 5 minutes, returning to the same plant repeatedly. Butterflies may rest on bare ground, in grasses, or on foliage, and may fly long distances (hundreds of meters) for nectar or to escape windy and foggy conditions. Mating usually takes place in relatively sheltered areas.

Fdult Oregon silverspot butterflies feed on nectar, which is their only food source, besides internal reserves present when they emerge from the pupae. Plants in the sunflower family (Asteraceae) dominate as nectar sources, including thistles (Cirsium spp); gumplant (Grindelia stricta); goldenrods (Solidago spp); tansy ragwort (Senecio jacobaea), California aster (Aster chilensis), pearly everlasting (Anaphalis margaritacea), seaside daisy (Erigeron glaucus), and yarrow (Achillea millefolium ). Nectar species from other plant families include sea-pink (Armeria maritima).

General Habitat Characteristics:

The Oregon silverspot butterfly inhabits three types of grassland habitats, including:

  1. coastal terrace and headland “salt spray” meadows, such as occur at Cascade Head, Rock Creek, and Bray Point in Oregon;
  2. coastal dune systems, such as occurs in the Del Norte County site; and
  3. montane grasslands, which characterize one Oregon site (Mount Hebo).

The first two habitats are strongly influenced by proximity to the ocean, with mild temperatures, moderate rainfall, and frequent summer fog. An occupied or potential site must have two key resources:

  1. caterpillar host plants; and
  2. adult nectar sources, as well as other suitable environmental conditions.

Distribution of the Oregon silverspot butterfly is highly dependant on these resources. The larval food plant, violets - in particular the early blue violet - must be present. At Lake Earl, populations of Aleutian violets (Viola langsdorfii) grow in wet areas adjacent to areas with early blue violets, and may serve as secondary food plants for silverspot caterpillars. Nectar sources need to be available to adults during the summer flight period. In addition to violets and nectar plants, areas with shelter from wind may affect habitat suitability. Silverspot sites are frequently windy during the butterfly flight season. Trees and large shrubs, as well as topographic features, can provide sheltered pockets, where microclimates are more favorable to butterfly flight and essential activities during windy periods.

Population and Habitat Status:

The Nature Conservancy (TNC) has conducted annual censuses for Oregon silverspot butterflies at four central coast sites in Oregon since 1990. While reports indicate that populations may have been relatively stable between 1985 and 1990, the annual censuses since then indicate a marked decline at three of the four sites since 1990 (all except Mount Hebo).

Little is know about the status of the Del Norte County population. The US Fish and Wildlife Service’s Arcata office initiated annual surveys in 2005, using the method employed by TNC in Oregon. Two years of data are too little to evaluate trends, but the 2005-2006 surveys indicated that the Del Norte population was among the largest remaining populations, although considerably smaller than Mount Hebo.

The four occupied Oregon sites occur on either federal lands under management of the U.S. Forest Service (3 sites), or TNC (Cascade Head). The Del Norte site includes State and private lands. Habitat management intended to benefit butterfly populations occurs at all the Oregon sites, and is planned for public portions of the California site.

The coastal grassland habitats used by Oregon silverspot butterflies are maintained by a combination of soil conditions unfavorable to woody vegetation, salt spray and mist, and disturbance regimes. Thin rocky soils at some sites, and sandy soils of dunes systems at others, favor the open low grassy vegetation used by silverspot butterflies. Disturbance also helps maintain grasslands, but disturbance regimes have changed dramatically over the past century, generally resulting in less large-scale disturbance. Notably, sand dune ecosystems have been stabilized by plantings of trees, and introduction of non-native European beachgrass and other vegetation. Fires are much less common than in earlier centuries, when fires set by Native Americans maintained open habitats. As a result of fewer fires, the extent of coastal grasslands has declined dramatically in Oregon, being replaced by shrubby and forested habitats not suitable for silverspots. The spread of non-native plants such as Scotch broom and introduced grasses has also degraded and eliminated habitat for the Oregon silverspot butterfly.

Threats:

The primary threats to the Oregon silverspot butterfly are habitat destruction due to development and agriculture, habitat fragmentation and degradation due to exotic plant invasion, natural succession of grasslands to forest and other habitats, off-road vehicles, livestock grazing, and erosion. Collisions with vehicles, impacts of pesticides, and collection for illegal trade are also potential problems, as is the lack of periodic disturbances, such as by fires, which help maintain coastal prairie habitats.

Conservation Needs:

Immediate conservation needs of the Oregon silverspot butterfly include preventing the further loss and degradation of known and suitable habitat within the range of the Oregon silverspot butterfly. The recovery plan includes these priority actions:

  1. maintain existing populations, especially in areas where most of the habitat is unprotected or unmanaged (including Del Norte County, California), or where populations are low or declining; and
  2. protect and enhance existing habitat in each of six conservation areas identified in the recovery plan (Long Beach Peninsula, Clatsop Plains, Coastal Mountains, Cascade Head, Central Oregon Coast, and Del Norte). Also needed is research to better understand the species’ ecological and management requirements, and management and monitoring of protected habitats to deal with ongoing threats.
Related Documents:

No other related documents, other than those listed in the general information section above.

Other Informational Weblinks:

Last updated: April 11, 2011

Arcata Fish and Wildlife Office, 1655 Heindon Road, Arcata, California 95521, USA
Tel: (707) 822.7201 Fax: (707) 822.8411