THE ENDANGERED MISSION BLUE BUTTERFLY OF CALIFORNIA
INDICATOR OF AN IMPERILED NATURAL ECOSYSTEM

Larry J. Orsak

Figure 1: Mission blue butterflies often perch on perennial lupine, the caterpillar's food.

INTRODUCTION

The mission blue butterfly (Icaricia icarioides missionensis; Figs. 1, 2) received federal protection as an endangered species in 1976, because much of its original, limited San Francisco area habitat had become unsuitable or was slated for urban development. It inhabits an ecosystem occupied by other unique plants and animals.

Figure 2: Endangered mission blue butterfly. Male.

DESCRIPTION

First described in 1937 (Hovanitz, 1937), the mission blue has a wingspan of about 25 millimeters (1 inch). The male (Fig. 2) is iridescent blue on the upper wings, with narrow black and pale white margins. The female is primarily brown, though often with some iridescent blue overlay. Below, males are grayish; females are grayish-brown. Both sexes are marked with an array of dark spots on their undersides. The Pardalis blue (Icaricia icarioides pardalis), the common San Francisco bay region subspecies, is represented by populations occurring just north and south of the mission blue colonies. The mission blue is usually distinguished from the Pardalis blue by the lighter underside spotting, the somewhat smaller size, also the presence of some blue on the female wing top surfaces. The latter character is never found in Pardalis blue females.

Figure 3: San Francisco Bay Region, showing mission blue butterfly distribution.

RANGE

The mission blue now occurs only in northern San Mateo County (San Bruno mountain and a small colony on the Milagra Ridge), San Francisco County (Twin Peaks, Fig, 4, and McClaren Park), and Marin County (small pockets on the Southern Headlands and Fort Baker, Fig.3). The Twin Peaks population is substantially reduced from its former size, surviving primarily on the southeast natural remnant. San Bruno mountain (Fig. 5) harbors the largest populations, primarily on the eastern, north-eastern and southern slopes (Arnold, 1979; Thomas Reid Associates, 1982).

LIFE CYCLE

One generation of mission blue occurs per year. Its life cycle closely resembles that of other Icaricia icarioides subspecies, as confirmed by Arnold (1979).

Eggs (Fig. 6A) are laid on leaves, buds and seed pods of the perennial lupines Lupinus albifrons (Fig. 7), L.formosus(Don&bue, 1975) and L. variicolor (Arnold, Ibid). The tiny caterpillars feed for a short time (Fig. 6B), then crawl to the foodplant base and enter a dormant state (termed "diapause") until the following spring.

Figure 5: San Bruno Mountain, looking west from San Francisco bay. Eastern grassland habitat supports low density mission blue populations. The ridges above brisbane (lower right) are prime sites to see the mission blue during May and June. The San Francisco silverspot, today only on San Bruno Mountain, inhabits the same sites.

At some point during very late winter to early spring (depending on the microenvironment of eachcaterpillar), the larvae resume feeding. Periodically the caterpillars shed their outer skin to accommodate growth.

Congregations of native ants on lupine may indicate the presence of larger mission blue larvae (Fig. 6C). The ants often stand on the sow bug-shaped caterpillar, tapping it with their antennae (Fig. 6D). The caterpillar secretes honeydew, a sweet substance eaten by the ants. In return, the ants probably ward off predators and parasites of the mission blue caterpillar. Thus, both ants and butterflies profit to some extent from this relationship. While this ant-caterpillar relationship is not unique (recorded for many members of the butterfly family Lycaenidae), it is an excellent example of the specialized interrelationships occurring among species of an ecosystem. ss

Full-grown caterpillars attach themselves securely to a surface, often a lupine stem or leaf. They then shed their outer skin once more, revealing a quite different outer covering, that of the pupa (chrysalid) (Fig. 6E).

The pupal stage lasts about ten days, during which the new adult butterfly develops within. It ends with emergence of the adult.

Mission blue butterflies can be observed as early as late March (near summit, San Bruno mountain; Twin Peaks) well into June (near Brisbane; San Bruno mountain). They are often seen perched on a lupine food plant, or nectaring at coastal buckwheat (Eriogonum latifolium) flowers (Arnold, Ibid). However, adults are often overlooked and are seldom abundant. This is because, unlike related inland subspecies, whose adults all fly within a three to four week period, mission blue adults emerge only a few at a time over an extended time period (Fig. 8) (Langston, 1975). This may be attributed to the cool and widely varied coastal climate, which can greatly prolong larval development.

Figure 7: The Gray bush lupine (Lupinus albifrons) is a major caterpillar food for the mission blue.

REQUIRED HABITAT

Mission blue scarcity is also due to the distribution of its lupine foodplants. Lupines grow best in grassland and rocky habitats lacking taller plants that might crowd them out. The lupine foodplants occur in low density even within favored natural areas, often clumped in small pockets. Mission blues must often travel many meters to locate their foodplants, thus spreading out over the grassland.

THREATS TO SURVIVAL

The Twin Peaks mission blue locale has special scientific significance as the "type locality," the site where specimens used to describe the subspecies were collected. Housing construction reduced that colony to its present remnants, which are constantly trampled by visitors to this classic vista point.

Most crucial to the butterfly's survival is protection of its largest habitat remnant on San Bruno mountain. Much of the mountain is now included within a county and a state park, but considerable mission blue habitat lies beyond, on land partially slated for development (Fig. 9). An estimated 16 of the total mission blue population inhabits San Bruno mountain's northeast ridge (Thomas Reid Associates, 1982). During 1980 and 1981 (Thomas Reid Associates, 1980, 1982), an intensive biological study was conducted on the mission blue and other equally rare (but not federally protected) San Bruno mountain inhabitants, necessitating the largest butterfly marking study ever conducted. One of the project's goals was to determine what, if any, development might allow the long-term survival of the rare and endangered species. Since further habitat elimination could jeopardize the species' long-term survival prospects, the study also sought to identify management practices (such as periodic fire) which would be required for maintenance of grassland habitat remnants. The "Habitat Conservation Plan" which was the end result of the biological study (San Bruno Mountain Steering Committee, 1982) estimates that as much as 13 of the total mission blue habitat will be eliminated through the major development planned for San Bruno mountain; it is envisioned that at least one-quarter of this will be reclaimed after construction (Ibid). However, by Summer 1994 no true reclamation has taken place. For example, the south slopes land (S.S.F., Terrabay, Inc. bankrupt by 1991) which is now under (he control of U.S. Resolution Trust Corporation, R.T.C.) is simply eroding and weed infested. This H.C.P. has caused the unraveling of the mission blue/silverspot habitat.

Figure 8: Seasonal Chronology of the mission blue life cycle. Adapted from data in Arnold (1978), Donahue (1975) and personal observations. Black areas within cross-hatching show the seasonal occurrence of a typical mission blue individual: cross-hatching indicates amount of seasonal variation found for the subspecies as a whole.

INDICATOR OF A UNIQUE ECOSYSTEM

Proponents of housing development on San Bruno mountain grasslands earlier portrayed the mission blue as the sole obstacle to development. This is incorrect. The mountain, small by many standards, represents the largest remaining tract of natural habitat on the northern San Francisco peninsula. As such, it harbors remnant populations of species endemic (found nowhere else) to the San Francisco peninsula. Indeed, San Bruno mountain harbors at least ten plants considered "Rare and Endangered" by the California Native Plant Society (two occur only there), and three others considered worthy of periodic population monitoring.

Figure 9: Signifcant mission blue populations inhabit San Bruno Mountain's northeast ridge. Looking northeast. Approximately 1200 housing units are planned for here, leaving about 60% of the northeast ridge as open space.

Besides the mission blue, another federally protected butterfly, the San Bruno elfin (Callophrysmossii bayensis) (Fig. 10), has its population stronghold on the mountain. Furthermore, there exist unverified San Bruno mountain reports of the endangered San Francisco garter snake (Thamnophissirtalisstrataenia). Another butterfly proposed for "Endangered" status, the Bay checkerspot (Euphydryas editha bayensis), survives at three sites, one being a small serpentine area on San Bruno mountain. And the San Francisco silverspot butterfly (Speyeria callippe callippe) now flies only on San Bruno mountain.

Butterflies are not the only rare San Bruno mountain insects: The wild bee Dufourea stagei is known only from San Bruno mountain and one other site in the nearby Santa Cruz mountains. Significant populations of the San Francisco tree lupine moth (Grapholita edwardsiana), which occurs only on sandy northern peninsula sites, were found by J. A. Powell and,R.A' Arnold at several of the mountain's sandy habitat remnants (Arnold, 1980).

Of all these rare or endangered species, at least seven prefer grassy habitats. Thus, destruction of a unique habitat harboring many highly localized species is the true issue, not the elimination of one butterfly.

Figure 10: Numerous highly restricted San Bruno mountain plants and animals, make this site a significant natural resource. Here, the federally protected San Bruno elfin butterfly nectars at the very rare coast rock cress (Arabis blepharophylla).

SAVING AN ECOSYSTEM: INVESTING FOR THE FUTURE

The importance of protecting unique natural ecosystems having a diversity of restricted organisms becomes apparent when one realizes that human survival has greatly depended on an ability to exploit other organisms for our benefit such as crops, domesticated animals and experimental subjects. Scientists are constantly discovering potentially useful attributes in little known, often nondescript species. Consider butterflies alone. Research on the African mocker swallowtail butterfly (Papilio dardanus) brought the answer to how "Rhesus babies," a human genetic disease, come about (Clarke, 1967). A Taiwanese butterfly (Catopsilia crocale) is being studied after an anti-tumor agent was found to occur in its wings (Brewer, 1976). The San Bruno mountain-inhabiting Bay checkerspot butterfly, subject of a 20-year study by Dr. Paul Ehrlich and colleagues at Stanford University, has produced information which might be applied to problems as diverse as insect pest population control, as well as wild game management (Ehrlich, et al, 1975).

Thus, it makes ecological and economical sense to protect as much of the earth's gene pool as possible. Once lost, genes cannot be recreated. Our own long term survival depends upon the continued healthy existence of the earth's many unique creatures and ecosystems.

Yes, the decision to save or pave the mission blue's special habitat will have implications far beyond the fate of one small butterfly. Hopefully the mission blue will continue to be an indicator of a unique ecosystem rather than symbolic of a destroyed national resource.

ACKNOWLEDGEMENTS: The following individuals criticized drafts of this leaflet. Their help was indispensable and is gratefully acknowledged: Richard Arnold, Karolis Bagdonas, JohnDeBenedictis, Robert Dirig, and Robert Pyle.

REFERENCES

Anonymous. 1980. The endangered San Bruno elfin of California. XercesSoc. Educational Leaflet 6. 4pp.

1981. The endangered San Francisco silverspot butterfly of California. Xerces Soc. Educational leaflet 5. 4pp.

Arnold, R. A. 1979. Status of six endangered California butterflies, 1977 . Report to the Calif. Dept. Fish & Game. 93pp.

1980. Status of proposed threatened or endangered lepidoptera. Report to the Calif. Dept. Pish & Game. 65 pp.

Brewer, J. 1976. Butterflies. Harry Abrams: New York 176pp.

Clarke.CA. 1967. Prevention of Rh-haemolytic disease. British Medical Journal 4:7-12 (7 October issue.)

Bay Area Land Watch. 1981. Rare and endangered San Bruno mountain wildlife.

1994. Habitat Conservation Plans under the Endangered Species Act.

Donahue, J.P. 1975. A report on the 24 species of California butterflies being considered for placement on the federal lists of endangered or threatened species. Report for the Calif. Dept. Food&Agric 58pp.

Ehrlich, P. R., R. R. White, M. C. Singer, S. W. McKechnie, & L.E. Gilbert. 1975. Checkerspot butterflies: a historical perspective. Science 182: 221-228.

Hovanitz, W. 1937. Concerning the Plebejus icarioides Rassenkreis (Lepidoptera, Lycaenidae). Pan-Pacific Entomologist 13: 184-189.

Langston, R. L. 1975. Extended flight period of coastal and dune butterflies in California. Journal of Research on the Lepidoptera 13:63-98.

San Bruno Mountain Habitat Conservation Plan Steering Committee. 1982. San Bruno mountain area conservation plan. 2 vols. 112 pp. + 284 pp.

Thomas Reid Associates, 1980. Phase one report to the San Mateo County steering committee for San Bruno mountain. Endangered species survey. San Bruno moun tain. Biological study, 1980.

1982. Endangered species survey. San Bruno mountain. Final report to the San Mateo County steering committee for San Bruno mountain. 260 pp.

Adapted from San Bruno Mountain Watch Education Leaflet Series No. 7
Photos from the Vault
First Printing: Xerces Society, June 1982
Second Printing: Bay Area Land Watch, April 94