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Lotis Blue Butterfly
Lycaeides argyrognomon lotis (also known as Lycaeides idas lotis)

General Information

Official Status: Endangered, the lotis blue butterfly is federally listed under the Endangered Species Act as endangered.

Date Listed: June 1, 1976; Federal Register: 41 FR 22041 (pdf, 500 KB).

Critical Habitat:Critical habitat for the Lotis Blue Butterfly has not been designated.

Recovery Plan: A Lotis Blue Butterfly Recovery Plan (pdf, 1.2 MB) was published in December1985

Male Lotis Blue Butterfly, Photo Credit: USFWS File Photograph

Male Lotis Blue Butterfly

Photo Credit:USFWS File Photograph

arrow button Photo Gallery for the Lotis Blue Butterfly

Identifying Characteristics:

The lotis blue butterfly is a small butterfly, with a wingspan averaging of about 1 inch (2.5 cm).  The upper wing surfaces are a deep violet-blue in the male, with a black border and fringe of white scales along the outer wing margin.  In females, the upper wing surface is brown, or sometimes bluish-brown, with a wavy band of orange near the outer margins of the wings, and an inconspicuous black border and fringe of white scales along the outer wing margins.  The wing undersides in both sexes are a grayish-white with scattered black spots, with a band of small orange spots bordered by black toward the outer wing margins.  The species Lycaeides argyrognomon, whichincludes the lotis blue butterfly and 12 other subspecies or forms, is also referred to Lycaeides idas, or Plebejus argyrognomon, and as the northern blue butterfly.  The northern blue butterfly occurs across northern North America.  The lotis blue occurs at the southwestern edge of the northern blue butterfly’s range.

Blue butterflies can be difficult for non-experts to identify, but the lotis blue butterfly is distinguished from other subspecies of Lycaeides argyrognomon by its large size, the size and pattern of the orange and black spots, and whitish underside wing color.

Current Geographic Range:

Historically, the lotis blue butterfly was found at several coastal locations in California, primarily in Mendocino County, but also in northern Sonoma County, and possibly northern Marin County.  Unfortunately, location information for most of the historic lotis blue butterfly sites is vague, and is based on specimens collected prior to the 1950’s. The one exception is a population discovered in 1935, north of the town of Mendocino.  Over the years, this site was visited by many lepidopterists and was the only certain location for the species from the 1950’s until the last confirmed observation in 1983.  The subspecies has not been observed since 1983.

Life History:

The life history of the lotis blue butterfly, like so much about this butterfly, is based on the known life history of closely related subspecies of the northern blue butterfly.  The lotis blue probably has a single generation per year, with a relatively long adult flight period, extending from mid-April to early July.  Eggs are likely laid during the adult flight season.  Newly hatched larvae begin to feed immediately, then overwinter in dormancy (diapause) as small larvae, then resume feeding the next spring.  The larvae (caterpillars) probably feed for about 4-6 weeks in the spring before pupating.  Lotis blue larvae have apparently not been observed; therefore we do not know what plants the larvae require for food.  Based on closely related species, native plants in the pea family (Fabaceae) are likely candidates.  The coast trefoil (also known as seaside bird’s-foot trefoil) (Lotus formosissimus) is thought to be a larval food plant.  The coast trefoil is a small perennial plant that generally occurs in damp areas in meadows, roadside ditches, and forest edges and clearings.  This plant grew at the last known lotis blue site, and there is a report of a lotis blue butterfly showing egg-laying behavior on coast trefoil, although no egg was observed.  Other possible food plants include herbaceous species of lupine.

General Habitat Characteristics:

The lotis blue butterfly probably occurred in wet meadows and sphagnum willow bogs. As noted above, the suspected food plant for larvae is the coast trefoil, which is relatively common along the Mendocino coast in damp coastal prairie.  Although the last known location was a sphagnum bog within pygmy forest, the coast trefoil is not normally found in bogs within the historic range of the lotis blue butterfly.  The importance of bogs to lotis blue butterflies is unclear.  The last known site for the species was located in a sphagnum bog surrounded by pygmy forest dominated by Bishop pine (Pinus muricata) with an understory of species in the heath family.  This suggests that such bogs may be at least one lotis blue habitat.  However, a recent extensive survey for lotis blue butterflies found that pygmy forest bogs did not provide many potential larval food plants, and suggested that bogs may not be typical habitat for the lotis blue.  Also, a powerline corridor ran through the last known lotis blue site, thus it may not have been a typical, natural bog.  Without knowing the larval food plant with certainty, the specific habitat characteristics for the species will remain something of a mystery.

Population and Habitat Status:

The lotis blue butterfly may be the rarest butterfly in North America.  The species has not been observed since 1983, despite many surveys at the last known site.  Extensive surveys of historic and potential sites in 1991 and again in 2003-2004 did not find the lotis blue either.  However, not all potential habitat has been surveyed, and the lotis blue butterfly may persist at one or more sites.

Threats:

Threats to the species are unknown, given our limited knowledge of the lotis blue.  The butterfly may have been naturally rare, and may have further declined due to natural factors such as a drying climate trend, or vegetation community changes over long time periods.  Changes in land use and management in historic times have contributed to vegetation changes within the historic range of the species, and may have affected the species.  Suppression of fires and other changes that reduced disturbance are suspected to have led to the transition of more open habitats, such as meadows, forest openings and coastal prairie, to areas dominated by forest and other taller, denser vegetation.  Development for housing and associated road-building has increased in recent decades, leading to loss and degradation of native habitats, and fragmentation of remaining habitat areas.  Because the butterfly may be associated with bogs and other wetland habitats, actions which affect groundwater may also affect the habitat for the species.

Conservation Needs:

A primary conservation need is to locate one or more populations of the lotis blue.  Should this happen, a priority need, in addition to protecting and managing the sites for the species, would be to study the lotis blue sufficiently to understand its basic biology and habitat needs, including what plant species the caterpillars require for food.  With this information, we would know better where to search for the lotis blue, and how to manage lands to conserve and restore the species within its historic range. 

Related Documents:

Lotus Blue Butterfly 5-year Review: Summary and Evaluation

Other Informational Weblinks:

Last updated: May 17, 2011

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