Mission blues (Icaricia icarioides missionensis) have only ever been found in the San Francisco Bay Area.
They are one subspecies in the Boisduval's blue complex, near only one other subspecies at a handful of sites.
Study Area
We used data from sites in in Marin and San Mateo Counties, California.
Natural History
Host Plant
Mission blues consume lupine leaves as caterpillars. They have three known hosts: the silver lupine (Lupinus albifrons), summer lupine (L. formosus), and many colored lupine (L. varicolor).
Flowering lupine.
Nectar Plants
Mission blues are nectar generalists, frequently observed nectaring on lupines and various plants from the sunflower family (Asteraceae).
A mission blue butterfly drinks nectar from a cluster of yellow and white flowers.
Mutualistic Relationship
Ants "tend" spring Mission blue caterpillars in a mutualistic relationship, giving protection from predators and parasites in exchange for sweet "honeydew" secreted by the caterpillars.
Habitat
The Mission blue requires a larval host plant and appropriate nectar plants in a coastal grassland habitat.
A Mission blue butterfly perches on a grass seedhead.
A Mission blue butterfly perches beside purple flowers.
The ocean and a view of a bridge in Marin County, CA.
A Mission blue butterfly perches on a pink flower.
Mission blue and habitat
Population Dynamics
Mission blue butterflies are distributed in two isolated populations with little probability of immigration between the two. Within the populations, metapopulation networks exist where there are hostplant patches.
Most butterflies remain near their host and nectar plants, rarely traveling more than 500 meters from their habitat patch.
The exact population size is unknown, though populations surveyed on National Park Service land suggest that there are at least 20,000 individuals remaining.
Life Cycle
Adult
Adults fly April-May, during which time they feed on nectar plants, mate, and lay eggs. They produce one brood each year (univoltine).
A Mission blue butterfly perches on green leaves.
Egg
Mission blue eggs are laid singly on lupines as early as March until July, hatching throughout the spring and early summer.
Closeup of a Mission blue butterfly egg.
Caterpillar
Caterpillars emerge from their egg and consume lupine, then overwinter beginning in July as second instars and emerge in February, when continue eating and recruit ants.
A Mission blue caterpillar crawls along the leaves of its host plant.
Chrysalis
After four weeks of feeding, caterpillars move to leaf litter to form their chrysalis.
Conservation
Listing Status
The Mission blue was listed as federally endangered in 1976. Protections from the Endangered Species Act have limited private and public ventures that further destroy coastal scrublands, but their remaining habitats are being degraded by invasive grasses, ongoing succession from fire suppression, and fungal pathogens targeting lupine hosts.
Recovery Efforts
Habitat Restoration
Prescribed burning, grazing, and tree removal return the landscape to its early successional stage. Invasive plants are also removed manually and with herbicide.
During the prescribed burn, managers marked lupine plants to avoid trampling them.
Blue flags marking the locations of Mission blue hostplants, prior to a prescribed burn.
Management
Habitat management for the Mission blue is focused on restoring coastal scrubland.
To the right, a prescribed burn is conducted in the Marin County headlands. Flames are contained to metal burn boxes to localize the management and protect lupine patches from accidental burns.
A prescribed burn in the Marin County headlands.
Population Trends
We analyzed seven sites for Mission blue, with the data ending in 2010 for most sites when captive rear and release began. We saw variable trends in abundance, and delays or no change in phenology.
Example activity index through time for Mission blue.
Example activity index through time for Mission blue.
