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Photo Credit: Sarah Swenty / USFWS
Mission Blue Butterfly
Icaricia icarioides missionensis
Basic Species Information
Endangered. This species is in danger of extinction throughout all or a significant portion of its range.
The mission blue is a small, delicate butterfly, in the Lycaenidae (gossamer-winged butterfly) family. Wingspread is about 2.5 to 3.6 cm. (about 1 to 1.5 inch)
Males and females have very different wings. The tops of males' wings are iridescent blue and lavender. Females' wings are dark brown with blue at the base.
In both males and females, wing edges are black. They have fringes made of long white hair-like scales. The undersides of the wings are whitish with small gray and larger black circles. There are no spots on the upper surfaces of the wings. The body of the male is dark bluish brown.
Adults drink flower nectar from buckwheat, golden asters, wild hyacinths and other plants. Caterpillars eat only lupine.
Coastal chaparral and grasslands.
Adult mission blue butterflies can be seen flying around from about late March to early July. Each of them only lives about a week.
Females lay eggs on lupine plants throughout the mating flight. The eggs are laid singly on leaves, stems, flowers and seed pods. (A great place to look for pictures of plants is CalPhotos. Search for silver lupine, summer lupine or many-colored lupine.)
The eggs hatch into caterpillars in 4 to 7 days. These feed on the inner tissues of the lupine. Flowers are entirely consumed. Then the caterpillars crawl into the leaves at the base of the plant.
When a caterpillar crawls into leaves, it becomes a pupa. Pupae are very different from butterflies and caterpillars. If you saw a pupa, you would think it was part of a plant.
In the spring, the butterflies-to-be become caterpillars again. They are tended by ants. The caterpillars give off a sweet liquid called "honeydew" that attracts the ants. The ants protect the caterpillars from predators. One generation of butterflies is produced each year.
The mission blue butterfly was first collected in 1937 from the Mission District of San Francisco. A small colony is located on Twin Peaks in San Francisco. Some live at the Golden Gate National Recreation Area in the Marin Headlands. The species has also been collected from Fort Baker, Marin County.
Most of the mission blues live on San Bruno Mountain. The 3,600-acre mountain in northern San Mateo County has most of the remaining habitat for three endangered species. These are the mission blue, callippe silverspot and San Bruno elfin.
Colonies are located at sites ranging from 210 to 360 m (about 690 to 1,180-foot) elevation. Some colonies occur in the fog belt of the coastal range. Coastal chaparral and coastal grasslands dominate the vegetation type where colonies are found.
Based on the lack of sightings of the adults during the normal flight season since 2004, it is possible the mission blue butterfly is either on the verge of being extirpated from the Twin Peaks Natural Area, or has already been extirpated. Attempts at reestablishing this population are ongoing.
What appears to be a mission blue butterfly metapopulation is found in the southern portion of its range in San Mateo County. This metapopulation is a chain of distinct colonies that extend north from the San Francisco Peninsular Watershed, along Sweeney Ridge, and ends at Milagra Ridge. See the 5-year review.
It is thought that wasps, other insects and rodents may prey on pupae.
Present or threatened destruction, modification, or curtailment of the habitat or range of the mission blue butterfly due to private development projects no longer pose as serious of a threat to the species as they did at the time of listing. However, public infrastructure development projects remain a significant threat. All mission blue butterfly populations found on Golden Gate National Recreation Area properties are relatively safe from development activities that would destroy, modify or curtail habitat.
The outbreak of an unknown fungal pathogen that infected lupine host plants during the El Nino year of 1998 at Milagra Ridge and Twin Peaks represents a threat to the mission blue butterfly throughout its range. Although many of the lupine host plant patches, and the mission blue butterfly population along with them, have reestablished themselves at Milagra Ridge and have been reestablished at Twin Peaks, the fungus remains present in the soil. The potential spread and outbreaks of this pathogen poses a greater threat to small and isolated populations.
Nonnative grasses and forbs that have invaded California grasslands and the conversion to coastal scrub are serious threats to the two listed butterflies due to their ability to become more abundant while outcompeting or becoming more abundant than the larvae food plant and nectar plants.
WHAT YOU CAN DO
If you live near the San Francisco Bay, help restore the mission blue's home. Search the Internet for mission blue butterfly volunteer. People are needed to pull weeds and plant native plants.
Wherever you live, watch butterflies and consider planting a butterfly garden.
Photo Credit: David Wright/USFWS
Photos & More
More Information on the Mission Blue Butterfly is available on ECOS.gov
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Last updated: December 1, 2017