The Bay checkerspot (Euphydryas editha bayensis) is a butterfly endemic to the San Francisco Bay region of the U.S. state of California. It is a federally threatened species, as a subspecies of Euphydryas editha.

Since the 1980s the population of checkerspots, the Euphydryas species and subspecies, has been in serious decline. This particular subspecies had been the subject of extensive study by researchers at Stanford University since the 1960s. Thus its vulnerability, particularly in light of rapid land development taking place in the San Francisco Bay Area, was recognized by this group of researchers. Consequently, in 1980 they petitioned the U.S. government to list this checkerspot subspecies as endangered. This led to a prolonged and contentious review by the U.S. Fish and Wildlife Service involving scientists representing arguments for and others against listing and numerous public hearings. The service finally conferred federally threatened status designation in 1987.35366 Federal Register, Vol. 52. No. 181. September 18, 1987

Recently, two authors have advocated a reclassification for this subspecies of the checkerspot common to western North America, Euphydryas editha. The classification, to Euphydryas editha editha, is for reasons of historical precedence;Proposed Rule--Critical Habitats (PDF), Oct. 16, 2001, Federal Register. however, this has not been accepted by the scientific community.

Description

The Bay checkerspot butterfly is a medium-sized butterfly with a wingspan of slightly more than . As a member of the family Nymphalidae the checkerspot is part of a group of brush-footed butterflies. The insect's forewings are marked with black bands along the veins of the wing's upper surface. It is the black banding that gives the Bay checkerspot its unique appearance and its name. The bands contrast sharply with bright red, yellow and white spots.Bay Checkerspot Butterfly , U.S. Fish and Wildlife Service, Sacramento Field Office.

The Bay checkerspot differs from other checkerspots, with characteristics differing:

from the LuEsther's checkerspot (Euphydryas editha luestherae) by being darker, it also lacks the relatively uninterrupted red band on the outer wing which the LuEsther's checkerspot has. from the island checkerspot (Euphydryas editha insularis) by being not as dark and brighter red and yellow than, which lives on the Channel Islands and nearby mainland. from other subspecies such as the Quino checkerspot (Euphydryas editha quino) or the Mono Lake checkerspot (Euphydryas editha monoensis) by having black bands that give the Bay checkerspot a much more checkered appearance than they have.Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area (PDF), 443 pages, U.S. Fish and Wildlife Service.

The subspecies was first described, as Euphydryas editha var. bayensis, by Robert F. Sternitzky in 1937.

Life cycle

Adult butterflies emerge in early spring. The adults, which live an average of ten days emerge during a six-week period from late February to early May. The male Bay checkerspot typically emerges four to eight days before the female. The males have one goal, reproduction. They find and mate with a female immediately upon emerging. The male mates many times while most females mate only once during the flight season. Besides mating the adults spend time foraging for nectar and for the females, laying eggs.

The eggs are usually laid in March and April. The adult female will lay up to five masses of eggs which contain 2 to 250 eggs each. The eggs are deposited at the base of the dwarf plantain plant or less frequently the purple owl's clover or denseflower Indian paintbrush. The eggs take about ten days to hatch and upon emergence from the eggs the larvae grow for a period of two weeks or more during which they shed their skin until they reach their fourth instar. Any larvae that successfully enters the fourth instar enter a period of diapause that lasts through the entire summer. During diapause they spend time under rocks or within cracks in the soil. When the diapause ends they resume activity, feeding and move to complete their development into adult Bay checkerspot butterflies.

Diet

While the larvae are dependent on the host plants, mostly the dwarf plantain, for sustenance the adult butterflies live on nectar. They feed on a variety of plants associated with serpentine grasslands. Some of these plants include California goldfields, white turtlehead, desert parsley, scytheleaf onion, false babystars, intermediate fiddleneck and others. Female fecundity is dramatically affected by nectar availability.

Habitat

This subspecies of butterfly faces declining habitat which has contributed to its placement onto the list of federally threatened species. Like other endangered and threatened species of butterflies, in and around the Bay Area, the checkerspot is faced with rapid human development of areas once considered prime habitat. Development and the proliferation of invasive species, exotic non-natives that naturalize in the area, are two of the three most grave threats to this and several other species of butterfly. The greatest threat to the butterfly is likely the increasing emission of nitrogen in California.

Range

The historic range of the checkerspot included many areas around the San Francisco Bay. Most of the San Francisco peninsula, mountains near San Jose, Oakland Hills and several locales around Alameda County were once home to populations of the butterfly. The butterfly occurred in areas east, west and south of the Bay, from Twin Peaks to Mount Diablo in Contra Costa County, all the way south to Hollister. Many of these areas no longer support the subspecies as development of the area increased throughout the 20th century. Today the only known populations inhabit Santa Clara County. Disturbances, specifically the altered regimes of these disturbances (i.e. lack of fire) have, along with invasive grassland plants, induced decline in the population of the host plants.

The current range is much reduced and patchy at that. Of all occurrences of the butterfly known when the subspecies was listed as threatened in 1987, all in San Mateo County have disappeared. A reintroduction of 1000 larvae to Edgewood Park in February 2007 did not result in a re-establishment of a population at this location. The subspecies was last observed at San Bruno Mountain in 1985 and at Jasper Ridge Biological Preserve in 1998. All remaining known populations of the butterfly are in Santa Clara County. The U.S. Fish and Wildlife Service recommends that any area of appropriate habitat within the historic range should be considered "potentially occupied". One site in Santa Clara County that has a large source population, that may number in the hundreds of thousands, is near the city of Morgan Hill on a ridge line currently called Coyote Ridge; much of this was acquired by the Santa Clara Valley Open Space Authority and is scheduled to open in 2018 as Coyote Ridge Open Space Preserve.

In the area of Jasper Ridge Biological Preserve local populations were deemed extinct in 1998. The populations of butterflies at Jasper Ridge had been the subject of intensive study and research at the lead of Stanford biologist Paul Ehrlich. Ehrlich had studied the Jasper Ridge populations since 1960 and researchers were able to examine 70 years of climate data and conclude that gigantic fluctuations in local climate probably hastened the demise of the Jasper Ridge Bay checkerspot populations. Ehrlich contends that prior to Spanish settlement of California the Bay checkerspots were almost certainly ubiquitous in California. It was the inadvertent import of invasive plant species in the hay that settlers fed cattle that brought unnatural competition for the native plants that sustained the Bay checkerspot.

The butterfly and its host plants thrive in areas with serpentine soil, soils derived from the serpentinite mineral, and other ultramafic rocks. The habitat has been described as consisting of three general types. Type one is the primary habitat which occurs on native grasslands located upon very large serpentine outcroppings. Type two is secondary or "satellite" habitat "islands" which occur in native grasslands on smaller serpentine outcrops. These satellites are typically generating very robust populations of Bay checkerspots in favorable weather with good habitat conditions. Type three are the tertiary habitats. These areas are where both Bay checkerspot larva and the plants they feed on occur in non serpentine soils with similarities to serpentine derived soil.

The possible reclassification of Euphydryas editha bayensis would indicate a change in range for the Bay checkerspot because of several populations of checkerspot butterflies whose subspecific status has been uncertain. If the nomenclature change was accepted it could represent a range extension for the threatened butterfly.

Host plants

The Bay checkerspot depends upon plants in two different genera as a larva. The primary host plant is of the genus Plantago while the secondary host plants occur in the genus Castilleja.

Plantago erecta

Plantago erecta, or dwarf plantain, is one of the primary host plants in the genus Plantago for the Bay checkerspot butterfly. In many years, the plantain dries up causing the checkerspot larvae to seek a secondary host plant. P. erecta is native to California and only found in western North America. As the primary host plant for the Bay checkerspot, it is an important species for conservation of the butterfly. P. erecta is known variously as California plantain, English plantain, foothill plantain, dotseed plantain, and dwarf plantain. It is typically found in coastal sage scrub, foothill woodland, and chaparral biomes.Plantago erecta, Taxon Report, Calflora Database.

Castilleja exserta

Castilleja exserta is known by a handful of common names: exserted Indian paintbrush, sometimes red owl's clover, or purple Indian paintbrush. It is one of two secondary larval host plants of the butterfly that remains edible later in the season and acts as a backup when the dwarf plantain dries up. The plant can grow up to in height. It prefers mesas, slopes and open areas in ponderosa pine forests and poppy fields at elevations from 1,500 to 4,500 feet (1,370 m). The flowers bloom from March to May and are about 1.25 inches long (32 mm) and formed in dense spikes, they are magenta or purple on the lower corolla lips and have yellow or white tips. The bract, modified leaves, are a reddish purple and hold five to seven lobes, each about one inch long (25 mm).Purple, Mojave or Common Owl's Clover , Colby-Sawyer College. It ranges from middle to southern California, into southern Arizona and northern Mexico., Wildflowers, Marin County Open Space District.

The plant's original classification, Orthocarpus purpurascens, has been shown, after careful study, to have been incorrect. Study showed that it belonged to the genus Castilleja.

Castilleja densiflora

C. densiflora, commonly referred to as purple owl's clover is the second of two secondary larval host plants of the butterfly. Similar to C. exersta, it often remains green later into the spring than the butterfly's primary host plant. The plant is generally between in height and grows in small colonies. Flowers can be observed between April and July. Flowers are pink/purple to white/yellow with five petals with white lobes that form a yellow "beak" and "eyespots" on the lower lip, which resembles the face of an owl. The species can be found in a variety of habitats including: foothill woodland, mixed evergreen forest, northern coastal scrub, chaparral, yellow pine forest, and native grasslands.

Habitat conservation