MISSION BLUE BUTTERFLY
Status:
Endangered
Description: On the upperside of the wings, the
adult female is brown with some blue, and the male is light blue. Both
have blackish wing edges. The underside of the wings is off-white with
two rows of irregularly shaped black spots. The larva (caterpillar) is
light green with diagonal white bars on each segment.
Size: Adults are about the size of a quarter (21 –
33 mm). Larvae are very small and rarely seen.
Habitat: The Mission blue requires a host plant and
appropriate nectar plants in a coastal grassland habitat. The host
plants utilized by the Mission blue are silver lupine (Lupinus
albifrons), summer lupine (Lupinus formosus), and varicolor lupine
(Lupinus variicolor). Nectar plants include various composites
(Asteraceae) that grow in association with the lupines.
Range: Remaining populations of Mission blue
butterfly are found in only a few locations around the San Francisco Bay
area in California: the Marin Headlands (Marin County), the Skyline
ridges (San Mateo County), San Bruno Mountain (San Mateo County), and
possibly at Twin Peaks (San Francisco County). The historical
distribution of the species probably encompassed much of the coastal
scrub/grassland habitat of the northern San Francisco peninsula and
Marin County.
 Life Cycle: The eggs
are usually laid singly on the dorsal side of new lupine leaves, but may
also be laid on stems, flowers, and seed pods of the lupine. Eggs hatch
within 6 – 10 days, and the first and second instar larvae feed on the
mesophyll of the host plant. Approximately three weeks after eclosion,
the second instar larvae begin diapause, usually in the litter at the
base of the host plant. Diapause begins at about the same time that the
host lupine shifts its energy from leaf maintenance to flower and seed
production. Larvae remain in diapause for the rest of the summer and
through the winter, and emerge to continue feeding in the spring.
Pupation, which lasts about a week, occurs in the duff at the base of
the host plant or other plants. The adult flight period lasts from March
to June. Adults live for approximately one week, and females lay eggs
on the host plant. The complete life cycle of the Mission blue lasts one
year.
Food Source: Mission blue larvae will feed only on
the leaves of the three host lupines: L. albifrons, L. formosus, and L.
variicolor. Adults may drink the nectar of composite flowers (sunflower
family), using a long tube called a proboscis that extends from the
underside of the head.
Population: The San Bruno Mountain population is
estimated at 18,000 adults. The Skyline Ridges support approximately
2,000 adults, and there may be as many as 500 at Twin Peaks. The Marin
Headlands population has not been estimated, but is significant.
Behavior: Mission blue larvae spend most of their
time feeding on lupine leaves in a variety of weather conditions. Adults
spend their short lives mating, laying eggs, and nectaring. To locate a
mate, adults patrol around in patches of host plant, rarely straying
far from the lupine habitat. On rainy, cool, windy, or foggy days,
adults hide out underneath vegetation.
 Survival Threats: The
main threat to the Mission blue is habitat loss due to agricultural and
urban expansion. Various parasites and predators threaten the Mission
blue during its life cycle. Eggs and larvae are parasitized by other
insects, such as wasps and flies. Rodents prey upon both larvae and
pupae, and many pupae die due to desiccation. . The invasion of exotic
plant species, such as ice plant, pampas grass, broom, gorse, and
eucalyptus, also threatens habitat. Trampling of host plants, larvae,
and pupae by humans and dogs is also a problem in some areas.
Legal Protection: The Mission blue was added to the
Federal Endangered Species List in 1976, and is protected under the
Endangered Species Act.
|
