Moss' Elfin (Callophrys mossii): Cliffs, Stonecrops, Range

Anyone who has seen the older name Incisalia mossii can stop looking for a second butterfly. Wikipedia lists it as a synonym of Callophrys mossii, Moss’ Elfin, which Wikipedia also calls the stonecrop elfin and Schryver’s elfin. It is one of the smaller butterflies in this section, with a wingspan of 7/8 to 1 1/8 inches (2.2 to 2.8 cm), and it lives in patches on rock.

Identification

BAMONA describes the sexes separately. The upperside of the male is grayish brown with a tan patch on the inner margin of the hindwing. The female is light brown to tan with dark borders. The underside is where an elfin is identified in the field: coppery brown to purplish brown, with the inner half of the hindwing darker than the lighter outer half. The two-tone hindwing is the mark to look for, and the sources do not name look-alike elfins, so a photograph is worth keeping for confirmation.

Wikipedia gives the wingspan as 22 to 28 mm, the same as BAMONA’s figure converted. It recognizes six subspecies listed alphabetically, in California (bayensis, doudoroffi, hidakupa, marinensis, windi), on Vancouver Island (mossii) and in Colorado (schryveri). The species was first described by Henry Edwards in 1881 as a variety of another elfin, Thecla irus var. mossii.

Range and habitat

The range is patchy, with isolated populations from British Columbia south to southern California and east to Wyoming and Colorado. The habitat is rocky outcrops, woody canyons and cliffs. That fits the host plant: Wikipedia describes broadleaf stonecrop as a succulent found in many types of rocky habitat. In California, males perch on shrubs or at the tops of cliffs to watch for females; in Colorado they perch in gulches.

Life history and flight

There is one flight a year, from March to June. Eggs are laid singly on the underside of host plant leaves. Young caterpillars feed on leaves, and older ones on flowers and fruits, so the stonecrop must flower and fruit if it is to feed the whole caterpillar stage. The chrysalids hibernate. BAMONA reports adult food as “not reported,” which leaves an open question about what the adults visit in each region.

The caterpillar hosts are stonecrops of the family Crassulaceae. BAMONA lists Sedum, Sedella, Dudleya and Parvisedum species. Wikipedia gives examples: Sedum spathulifolium and S. lanceolatum.

The San Bruno Elfin

The conservation story is one subspecies, Callophrys mossii bayensis. BAMONA states that it is listed as Endangered by the US Fish and Wildlife Service and is limited to the San Bruno Mountains in San Mateo County, California, and a few nearby sites. It carries the Nature Conservancy rank T1, critically imperiled. The management need is to protect the habitat of the San Bruno Elfin and other limited populations from development and from encroachment by non-native plants.

The Wikipedia article on the subspecies adds the detail. Its patchy distribution reflects that of its host plant, broadleaf stonecrop (Sedum spathulifolium). Adults emerge in February and March, when nectar flowers open. The larvae feed first on the plant’s leaves and, when its flowers begin to open, move up and eat the flowers. By June most have finished and leave the plant to pupate in ground litter, and the pupae stay dormant until the next spring. The larvae also produce honeydew that attracts ants, which often protect them from predators and parasites. Beyond San Bruno Mountain, one colony is established at Montara, on coastal bluffs about 25 miles south, and a third near Rockaway Beach in Pacifica.

Wikipedia also records that habitat there was reduced by quarrying, off-road vehicles and urban development, and that a habitat management plan protects the elfin and the Mission blue butterfly, with reduced pesticide use, careful recreation management and vegetation management. Revegetation and reintroduction are targeted at areas where populations were lost.

What a gardener can and cannot do

Treat the species proper and the San Bruno Elfin separately. The species, outside California’s Peninsula, lives on cliffs and canyon walls, and none of the sources describes it visiting planted gardens. What they do support is that its host plants are ordinary stonecrops. Wikipedia describes Sedum spathulifolium as an evergreen perennial native from British Columbia to southern California, grown as an ornamental groundcover in well-drained soil in sun or part shade, and notes it dislikes winter wet; the cultivars ‘Cape Blanco’ and ‘Purpureum’ hold the Royal Horticultural Society’s Award of Garden Merit. So a gardener in the range can grow a host plant without strain. Whether elfins then find it is not documented.

For the San Bruno Elfin, the measures the sources list are habitat protection, control of non-native plants and managed recreation on a few rocky slopes; no source lists a garden measure. The butterfly garden guide covers the general rule that a garden needs host plants as well as nectar. For another small western butterfly tied to a single plant family, see the Lustrous Copper and its sorrels.