Myrtle's silverspot butterfly
Encyclopedia
Myrtle’s silverspot, Speyeria zerene myrtleae, is a medium-sized butterfly
in the brush foot family (Nymphalidae
), an endangered
subspecies
of Zerene fritillary
. It is endemic to California
, where it is known from only about four locations just north of the San Francisco Bay Area
, including two at Point Reyes National Seashore
. Its wingspan is approximately 2.2 inches (55.9 mm). The upper surfaces of the wings are golden brown with numerous black spots and lines. The undersides are brown, orange and tan with black lines and silver and black spots. Larva
e are dark-colored with many sharp branching spines on their backs. Myrtle's silverspot is larger and paler than the closely related Behrens' silverspot (Speyeria zerene behrensii), which is now limited to the vicinity of Point Arena in Mendocino County
.
The female lays a single brood of eggs in the dried herbage of violets, especially western dog violet
(Viola adunca), the only known larval food plant. Upon hatching, the caterpillars wander a short distance and spin silk
pads upon which they pass the winter. The larvae immediately seek out the food plant at the end of their diapause
in the spring. After 7 to 10 weeks each larva pupa
tes within a chamber of leaves it glues together with silk. Adults may emerge in about 2 weeks and can live for 3 weeks. The adult flight season may range from late June to early September. Adults feed on nectar from flowers including gumplants
(Grindelia spp.), yellow sand verbena
(Abronia latifolia), coyote mints
(Monardella spp., especially Monardella undulata
), bull thistle
(Cirsium vulgare) and seaside daisy
(Erigeron glaucus).
Myrtle's silverspot is found in sand dune
and coastal prairie habitat. Populations were formerly found in dunes and bluffs from San Mateo County
north to the mouth of the Russian River
in Sonoma County
. The populations south of the Golden Gate
apparently have been extirpated
by urban development. Four populations are known to inhabit coastal terrace prairie, coastal bluff scrub, and associated non-native grassland habitats in western Marin
and southwestern Sonoma Counties, including Point Reyes. Adult butterflies are typically found in areas that are sheltered from the wind, below 820 feet (249.9 m) elevation, and within 3 miles (4.8 km) of the coast.
The butterfly was listed as an endangered species
in 1992. Habitat loss due to residential and commercial land development has extirpated these butterflies from parts of their range and may threaten some of the remaining populations. Maintaining larval and nectar plants is critical for conservation of these butterflies. Changes in natural fire patterns
, introduction of exotic plants
, and successional changes
in the plant community have reduced the availability of host plants. Either excessive or inadequate grazing
activity can result in plant communities unfavorable to the butterflies. Measures for habitat improvement may include eradication of invasive exotics such as iceplant (Mesembryanthemum
spp.) and identifying appropriate grazing and/or burning regimes in grassland and scrub areas. These butterflies are highly prized by insect collectors, and are vulnerable due to their small population. Silverspot butterfly larvae are also extremely sensitive to pesticide
s.
Butterfly
A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...
in the brush foot family (Nymphalidae
Nymphalidae
The Nymphalidae is a family of about 5,000 species of butterflies which are distributed throughout most of the world. These are usually medium sized to large butterflies. Most species have a reduced pair of forelegs and many hold their colourful wings flat when resting. They are also called...
), an endangered
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
of Zerene fritillary
Speyeria zerene
Zerene Fritillary is a species of butterfly found in the western portions of the United States and Canada.-Description:...
. It is endemic to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, where it is known from only about four locations just north of the San Francisco Bay Area
San Francisco Bay Area
The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...
, including two at Point Reyes National Seashore
Point Reyes National Seashore
Point Reyes National Seashore is a park preserve located on the Point Reyes Peninsula in Marin County, California, USA. As a national seashore, it is maintained by the US National Park Service as a nationally important nature preserve within which existing agricultural uses are allowed to continue...
. Its wingspan is approximately 2.2 inches (55.9 mm). The upper surfaces of the wings are golden brown with numerous black spots and lines. The undersides are brown, orange and tan with black lines and silver and black spots. Larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e are dark-colored with many sharp branching spines on their backs. Myrtle's silverspot is larger and paler than the closely related Behrens' silverspot (Speyeria zerene behrensii), which is now limited to the vicinity of Point Arena in Mendocino County
Mendocino County, California
Mendocino County is a county located on the north coast of the U.S. state of California, north of the greater San Francisco Bay Area and west of the Central Valley. As of the 2010 census, the population was 87,841, up from 86,265 at the 2000 census...
.
The female lays a single brood of eggs in the dried herbage of violets, especially western dog violet
Viola adunca
Viola adunca is a species of violet known by the common names hookedspur violet, sand violet, and western dog violet. It is native to North America, including the western half of the United States to New England northward throughout Canada.This is a hairy, compact plant growing from a small rhizome...
(Viola adunca), the only known larval food plant. Upon hatching, the caterpillars wander a short distance and spin silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
pads upon which they pass the winter. The larvae immediately seek out the food plant at the end of their diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
in the spring. After 7 to 10 weeks each larva pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
tes within a chamber of leaves it glues together with silk. Adults may emerge in about 2 weeks and can live for 3 weeks. The adult flight season may range from late June to early September. Adults feed on nectar from flowers including gumplants
Grindelia
Grindelia is a genus of plants native to the Americas belonging to the family Asteraceae, . G. squarrosa, a plant with bright yellow flowers indigenous to much of the United States, is commonly called curlycup gumweed. G. robusta, found in the western states, is a coastal scrub bush that is...
(Grindelia spp.), yellow sand verbena
Abronia latifolia
The perennial flower Abronia latifolia is a species of sand-verbena known commonly as the coastal, or yellow sand-verbena. It is native to the west coast of North America, from southern California to the Canadian border....
(Abronia latifolia), coyote mints
Monardella
Monardella is a genus of 28 species of annual and perennial plants native to western North America. They are grown for their highly aromatic foliage, which in some species is used for herbal teas...
(Monardella spp., especially Monardella undulata
Monardella undulata
Monardella undulata is an uncommon species of flowering plant in the mint family known by the common name curlyleaf monardella.-Distribution:...
), bull thistle
Cirsium vulgare
Cirsium vulgare is a species of the genus Cirsium, native throughout most of Europe , western Asia , and northwestern Africa...
(Cirsium vulgare) and seaside daisy
Erigeron glaucus
Erigeron glaucus is a species of flowering plant in the daisy family known by the common name seaside fleabane, beach aster, or seaside daisy....
(Erigeron glaucus).
Myrtle's silverspot is found in sand dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
and coastal prairie habitat. Populations were formerly found in dunes and bluffs from San Mateo County
San Mateo County, California
San Mateo County is a county located in the San Francisco Bay Area of the U.S. state of California. It covers most of the San Francisco Peninsula just south of San Francisco, and north of Santa Clara County. San Francisco International Airport is located at the northern end of the county, and...
north to the mouth of the Russian River
Russian River (California)
The Russian River, a southward-flowing river, drains of Sonoma and Mendocino counties in Northern California. With an annual average discharge of approximately , it is the second largest river flowing through the nine county Greater San Francisco Bay Area with a mainstem 110 miles ...
in Sonoma County
Sonoma County, California
Sonoma County, located on the northern coast of the U.S. state of California, is the largest and northernmost of the nine San Francisco Bay Area counties. Its population at the 2010 census was 483,878. Its largest city and county seat is Santa Rosa....
. The populations south of the Golden Gate
Golden Gate
The Golden Gate is the North American strait connecting San Francisco Bay to the Pacific Ocean. Since 1937 it has been spanned by the Golden Gate Bridge...
apparently have been extirpated
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
by urban development. Four populations are known to inhabit coastal terrace prairie, coastal bluff scrub, and associated non-native grassland habitats in western Marin
Marin County, California
Marin County is a county located in the North San Francisco Bay Area of the U.S. state of California, across the Golden Gate Bridge from San Francisco. As of 2010, the population was 252,409. The county seat is San Rafael and the largest employer is the county government. Marin County is well...
and southwestern Sonoma Counties, including Point Reyes. Adult butterflies are typically found in areas that are sheltered from the wind, below 820 feet (249.9 m) elevation, and within 3 miles (4.8 km) of the coast.
The butterfly was listed as an endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
in 1992. Habitat loss due to residential and commercial land development has extirpated these butterflies from parts of their range and may threaten some of the remaining populations. Maintaining larval and nectar plants is critical for conservation of these butterflies. Changes in natural fire patterns
Fire regime
A fire regime is the pattern, frequency and intensity of the bushfires and wildfires that prevails in an area. It is an integral part of fire ecology, and renewal for certain types of ecosystems. If fires are too frequent, plants may be killed before they have matured, or before they have set...
, introduction of exotic plants
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
, and successional changes
Ecological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
in the plant community have reduced the availability of host plants. Either excessive or inadequate grazing
Grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
activity can result in plant communities unfavorable to the butterflies. Measures for habitat improvement may include eradication of invasive exotics such as iceplant (Mesembryanthemum
Mesembryanthemum
Mesembryanthemum is a genus of plants native to southern Africa. Many species which were formerly placed herein have since been moved into other genera such as Carpobrotus Sceletium is sometimes included here....
spp.) and identifying appropriate grazing and/or burning regimes in grassland and scrub areas. These butterflies are highly prized by insect collectors, and are vulnerable due to their small population. Silverspot butterfly larvae are also extremely sensitive to pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s.
Further reading
- Launer, A.E., D.D. Murphy, J.M. Hoekstra and H.R. Sparrow. 1992. The endangered Myrtle’s silverspot butterfly: present status and initial conservation planning. Journal of Research on the Lepidoptera. 31:132-146.
- Thelander, C. ed. 1994. Life on the edge: a guide to California's endangered natural resources. BioSystem Books. Santa Cruz, CA. p 436-437.
- U.S. Fish & Wildlife Service. 1988. Recovery Plan for Seven Coastal Plants and the Myrtle's Silverspot Butterfly. Portland, Oregon.
- U.S. Fish & Wildlife Service. 1992. Endangered and Threatened Wildlife and Plants; Six plants and Myrtle's Silverspot Butterfly from Coastal Dunes in Northern and Central California Determined to be Endangered. Portland, Oregon.