San Bruno Mountain's Rare and Endangered Butterflies

Three Endangered Butterflies in One Place!

Three rare and endangered butterflies struggle to survive on San Bruno Mountain - the Mission Blue, the San Bruno Elfin and the Callippe Silverspot. All are federally listed as endangered and San Bruno Mountain is the only place on the planet where these 3 species coexist. These rare butterflies have very specific habitat requirements - and butterfly habitat on San Bruno Mountain is under constant threat. Loss of habitat means loss of butterflies.

These three butterflies have several things in common:  all are subspecies of more common butterflies; all are host plant-specific - see description below; all have limited range; all have very short adult stages; all have one-year life cycles - explanantion of stages below; and all find their largest population here on San Bruno Mountain.

Click on the butterfly's name to go to its own page for specific information.


  Mission Blue Butterfly

Icaricia icarioides missionensis


  USFWS; public domain photo




 Listed 1976



 San Bruno Elfin Butterfly

Callophyrs mossii bayensis


  SBMW photo




 Listed 1976



 Callippe Silverspot Butterfly

Speyeria callippe callippe


  © Keith Moreau




 Listed 1997



Host Plant-Specific Butterflies - the importance of habitat protection

Butterflies require both nectar plants to feed adults and host plants to house and feed larvae (caterpillars). Many butterflies use a variety of plants (polyphagous butterflies) as host plants and those species tend not to be endangered - they have an easier time and can adapt to varied habitats.

Host-specific butterflies have a harder time - some may be able to use more than one species from one plant genus (the Mission Blue can use 3 different species of lupine), but frequently butterflies will rely solely on one plant species to lay their eggs and feed the larvae (caterpillars). The Callippe Silverspot, for example, must use the California Golden Violet (Viola pedunculata) and the San Bruno Elfin must use the Pacific Stonecrop (Sedum spathulifolium). Consequently, the disappearance of the host plant, for any reason, spells disaster - and the extermination of the species.

Butterfly Life Cycle - a yearlong process of metamorphosis

There are four stages in butterfly development: egg, larva (caterpillar), pupa and adult.

Egg:  This is where life begins.

Larva (caterpillar):  This is when most of the feeding and growth occurs. There are several stages of larval development, each stage called an instar (first instar, second instar, etc.) The larva molts between each instar stage.

Diapause: Our three butterflies spend about 85% of their life cycle in this hormonally-induced state of quiescence (period of inactivity). Each butterfly enters diapause at different developmental stages. For our three endangered species, diapause is at the larval or pupal stage of development.

Pupa:  The "magic" happens here as the full grown larva (caterpillar) becomes an adult butterfly. Some insect larva spin a cocoon but these three butterflies form a hard shell called a chrysalis after the full grown larva sheds its skin for the last time.

Adult:  The beautiful butterfly we enjoy must now mate and lay eggs for a next generation. The adult stage butterfly only lives for a couple of weeks.

Footnote:  Habitat is critical to San Bruno Mountain's butterflies. The major threats to loss of habitat are development, non-native invasive plants, and natural scrub succession. Plant succession is a natural process where a few species of plants expand to dominate a habitat when they have the opportunity and no negative factors. Succession can be slowed and reversed using a strategy of controlled burns, which also benefits the required host plants. All three species of endangered butterflies evolved with fire being a natural part of their environment and have adapted by spending the majority of their life cycle on the ground or in the ground around their host plant.