INTRODUCTION

The Callippe Silverspot Butterfly (Speyepia oallippe) is a spectacular sight as it flies through foothill or mountain terrain, its bright colors in contrast with the background landscape. Its wings, marked with orange-brown and variously shaped markings da the upper surfaces, span about 62.0 millimeters (2.5 inches). The wing undersides are lighter orange, usually speckled with contrasting silvery spots. First discovered by the gold-seeker-turned lepidopterist Pierre Lorquin, the species was described and named in 1852 by the French lepidopterist Boisduval. It has since been recorded from numerous localities in the western United States. Over this wide range, one finds great wing pattern variability: some populations consist of individuals which lack the undersurface silver markings; the underside background color is alao variable, ranging from green to brown to cinnamon; upper surfaces range from bright orange to dull yellow-brown, depending on location. The factors underlying this pattern variation are relatively little understood and this species could become a subject of long-term studies dealing with climatical effects on wing pattern as well as other ecological investigations. In drawing accurate conclusions from such research all the "puzzle pieces" should be available for study. Unfortunately, some of the Speyeria callippe pieces have been forever lost as populations disappeared due to habitat destruction.

Important Callippe Silverspot populations, both historically and scientifically, occur(red) in and near San Francisco, California. Since those specimens used by Lorquin to describe the species probably originated from this area, San Francisco received "type locality" designation for the species; specimens from there are thus considered most representative of the species as a whole. San Francisco area Speyeria callippe populations also differ in appearance from those of adjacent regions, showing more extensive black markings on the upper wing surfaces that result in a dusky appearance (Fig. 1). Lepidopterists have thus designated certain San Francisco area populations as a separate subspecies (Speyeria callippe callippe), apart from populations to the south (Speyeria callippe comstocki) or north (Speyeria callippe liliana). The pattern changes occur gradually as one moves north or south of the bay region; hence, any dividing line separating S.c. callippe from either S.c. comstocki or S.c. liliana becomes somewhat arbitrary. Still, the name Speyeria callippe callippe (we hence forth use the common name "San Francisco Silverspot" for this subspecies) refers in the strict sense only to populations on the San Francisco peninsula (San Bruno Mountains, north) (see Greenwalt, 1980). Those occurring at Redwood Regional Park in Oakland (Alameda County), near Vallejo (Solano County), and probably the Mount Hamilton Range (Santa Clara and eastern Alameda counties) (Fig. 2) are transitional between the subspecies S. callippe comstocki and S. callippe callippe. The San Francisco Silverspot can now be characterized as endangered within its narrow range; indeed, extinction of the subspecies may occur in the foreseeable future. In the following paragraphs, a synopsis of this butterfly's life history and habitat are presented, concluding with a prognosis for its survival.

LIFE HISTORY & HABITAT

Adults occur during a brief period each year from about late May to early July. Flying rapidly over the foothill terrain, they occasionally alight briefly on the ground or stop to visit flowers. The female spends much tine seeking clumps of the caterpillar foodplant, a yellow-flowering native violet, Johnny Jump-up (Viola pedunculata). The yearly foliage of this perennial plant has usually withered by June. The female locates these dying clumps and lays eggs on or near the leaves.

Eggs hatch within a few days. The very small emerging caterpillars crawl into the ground debris and enter a dormant state which extends through the summer and winter months. During the winter rainy season, the larvae again become active and commence feeding, primarily at night, on the new violet growth (Fig. 3). The full-grown caterpillars enter the pupal stage in May. This stage lasts about two weeks, ending with adult butterfly emergence.

The violet foodplant grows most profusely in grasslands, and the San Francisco Silverspot is generally restricted to such habitat. In contrast, the violet is rare or absent where taller plants predominate — for example, in the sage-scrub vegetation covering much of the bay area foothills. Periodic burns help maintain these grasslands. The fires do not kill the violets, which resprout the following season; they do eliminate taller growth which could outcompete these low-growing plants. Fire thus enhances San Francisco Silverspot populations by favoring the caterpillar foodplant. Although the degree to which fire directly affects adult survival and dispersal has not been documented, the following do occur: (1) San Francisco Silverspots will fly over burned areas within an hour following a blaze. (2) Violet foliage is not burned to ashes by early summer fires, since violets retain a higher moisture content than surrounding grasses — the leaves are only charred. (3) Violet clump visibility is enhanced following fire, when obscuring taller grasses are burned off (L. Orsak, personal observation in the San Brunos). Burned areas may thus be recolonized following a burn, if it happens during the adult flight season and intact Silverspot habitat occurs nearby. Even so, the higher temperatures of the post-blaze ground (due to plant cover removal and heat-absorbing properties of black ashes on the soil) could kill hatching larvae.

What effects do burns have, later in the season, after caterpillars become dormant? Richard Arnold (personal observation) has found that Silverspot caterpillars can survive grassland fires, since such relatively "cool" blazes usually move rapidly through the area — in contrast to the hotter, slow-moving brush and woodland fires. In windy conditions, grassland fires also burn in patches, leaving islands of unburned vegetation. Caterpillars lucky enough to occur in these areas might repopulate adjacent burned sites as adult butterflies.

PRESENT STATUS AND PROSPECTS FOR SURVIVAL

The San Francisco Silverspot was proposed for federal protection by the United States Fish and Wildlife Service in 1978, in view of past and foreseeable population extinctions.

The major site of known population extirpation has been San Francisco, where it probably no longer occurs. It was last seen there about 50 years ago. Former population sites in the City include Visitacion Valley and the Lake Merced area (Harriet Reinhard, personal communication). The only other site on the San Francisco Peninsula harboring populations are the grasslands at the eastern end of the San Bruno Mountains (Figs. 4, 5), south of San Francisco. Although both a county regional park and new state park encompass much of this range, very little San Francisco Silverspot habitat is included. Developments containing about 2200 homes are scheduled for most of this area, and the continued survival of the butterfly remains questionable.

The loss of these populations would mean the extinction of the San Francisco Silverspot subspecies, thus joining the large list of extinct San Francisco Peninsula organisms. But the destruction of the Silverspot habitat would also eliminate populations of many other organisms, including those of the Endangered Mission Blue Butterfly (Icaricia icarioides missionensis) (Fig. 6), which also occupies grassland habitats in the San Brunos.

How might the elimination of some Silverspot populations bring about the extinction of the subspecies as a whole? One must examine the biology and population dynamics of the butterfly for answer. Certainly, the Silverspot flew in greater abundance before the massive human influx, and it must have occurred in numerous colonies that were distinct, but not so isolated from one another as they are today. These populations were also subjected to periodic fire — a natural environmental feature — and exposed to other natural catastrophes such as drought. A long-term absence of fire creates a buildup of brush and debris. Subsequent fire burns slowly and is very hot, fueled by this organic debris accumulation. Such a fire might directly eliminate the butterfly from that site, or reduce its population, making it highly susceptible to other natural catastrophes. A population might also conceivably disappear due to inbreeding. In any case, these extinctions would be compensated by eventual recolonization of these and other sites as favorable habitat appeared. Although great fluctuations might occur in single populations, the overall San Francisco Silverspot population would maintain relative stability.

Unfortunately, extensive urbanization has markedly affected the butterfly's ability to colonize habitats in the San Francisco bay area. Greater distances of unsuitable habitat now separate remaining populations, thus reducing the chances of individuals from one site coming into contact with those from another, much less successfully recolonize a location. Of course, natural disappearances of populations would still be expected. Result? Populations would disappear one by one, until the Silverspot was extinct from the region.

This scenario is somewhat speculative, yet based upon biological theory. Indeed, the fact that three butterflies found only on the San Francisco Peninsula are now extinct gives the projections some credibility. And when one examines the sequence of events leading to their extinction, similarities between these butterflies and the San Francisco Silverspot become apparent.

THE XERCES BLUE STORY

All three San Francisco extinct butterflies seemingly disappeared before the destruction of all natural habitat. Indeed, the last known location of the Xerces Blue Butterfly (Glauco psyche xerces) remains undeveloped to this day, even possessing a few of its larval foodplants. The principal caterpillar food, Deerweed (Lotus scoparius), is an early colonizer of recently disturbed (shifting sand, fire) sites, outcompeted in a few years by other plants. Xerces Blue populations probably shifted locations as the foodplant sites changed. Local die outs of the Deerweed probably brought about occasional Xerces Blue population extinctions, but these were no doubt balanced by the butterfly's colonization of new areas. Urbanization eliminated most Xerces Blue populations during the 1930's, with the remaining vacant lot colonies surrounded by inhospitable city habitat. Fewer favorable habitats for Deerweed growth became available, and even these were unlikely to be found by the few remaining Xerces Blue butterflies. The Xerces Blue survived for awhile in this state, finally disappearing in 1942. Could the Xerces Blue story be repeated for the San Francisco Silverspot?

A POSSIBLE SOLUTION

Perhaps the Silverspot has already reached the "point of no return." Still, the best way to maximize its survival chances would entail preservation of a large continuous area in the San Bruno Mountains, containing several Silverspot populations in relative proximity to one another.

Protecting this habitat would bring added benefits: Additional sites of other resident rare/endangered organisms (particularly the Mission Blue Butterfly) would be procured. The habitat could also tolerate some forms of human recreation and the area would attain immense value as aesthetically pleasing open space within a large metropolis.

REFERENCES AND ADDITIONAL READING

Anonymous. 1978. The Endangered Mission Blue Butterfly of San Francisco. Xerces Society Educational Leaflet #1. 1-2,

1979. Extinct butterflies of San Francisco, California. Xerces Society Educational leaflet C4. 1-4.

1980. The Endangered San Bruno Elfin Butterfly of California. Xerces Society Educational Leaflet 6. 1-4.

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 California Department of Food and Agriculture. 58 pp.

Greenwalt, L. A. 1988. Endangered and threatened wildlife and plants; reproposal of critical habitat for one species of butterfly. Federal Register 45(62):205B3-20505>

Tilden, J. W. 1965. Butterflies of the San Francisco Bay Region. University of California Press: Berkeley & Los Angeles. 88 pp.

ACKNOWLEDGEMENTS.: THE ASSISTANCE OF LARRY ORSAK, RICBARD A. ARNOLD, HARRIET REINSARD, ROBERT DIR1G. ROBERT M. P!I£, ASD LAWRENCE F. GALL MADE THIS LEAFLET POSSIBLE.