Lustrous Copper (Lycaena cupreus): ID, Range and Host Plants

Look for a flash of copper low over a damp mountain meadow in July, and the butterfly is probably the Lustrous Copper, Lycaena cupreus. It is a small butterfly, about 1 1/8 to 1 1/4 inches across (2.9 to 3.1 cm), and it lives where the western mountains run out of trees: alpine meadows, sagebrush flats, glacial cirques and rocky ground. Its caterpillars eat sorrels and docks, and the adults visit flowers for nectar on one flight a year, from June to August. The French and English Wikipedia entries and the BAMONA species account agree on all of that, and the rest of this page sets out what each one adds.

How to recognize it

The upperside does the identifying. BAMONA describes it as shiny coppery red with small black spots and a black border, and the spots are larger on the female, which is the easiest way to sex a specimen at a glance. French Wikipedia adds a white fringe at the wing edge, slightly brown at the base. Turn the butterfly over and the underside is gray with many small black spots; the forewing carries an overall copper tinge and a black line near the margin, and the hindwing has a red line in the same position. Wikipedia gives the wingspan as 23 to 30 mm, a little narrower than the BAMONA figure, so expect some spread between individuals and between sources.

The caterpillar is rarely seen but described in French Wikipedia: green, with red lines along the flanks and small red dots on the back. That description comes from a single source and appears in none of the others checked, so it is a lead for a field guide to confirm rather than a fixed rule.

Where it lives

BAMONA states the range in two parts. In the Rocky Mountains it flies at high elevations from British Columbia south to New Mexico. On the Pacific slope it occurs at moderate to high elevations from Oregon to the Sierra Nevada of California, and it reaches western Nevada. French Wikipedia lists the same block of states and provinces, naming British Columbia and Alberta in Canada, and Washington, Oregon, Idaho, western Montana, Wyoming, northeastern Utah, Colorado, northern New Mexico, California and western Nevada in the United States.

The habitat list is short and consistent: mountain meadows, sagebrush flats, glacial cirques, rocky treeless areas. In other words, open ground above or beyond the forest. Males perch and patrol for females in hollows of open areas, which is where BAMONA places their courtship activity.

The sorrel connection

Everything about where this butterfly lives follows from what the caterpillar eats. BAMONA lists plants of the knotweed family, Polygonaceae, including alpine sorrel (printed as Rumex pauciflorus) and other Rumex and Oxyria species. Wikipedia names Oxyria digyna, mountain sorrel, and Rumex. A note on spelling: Wikipedia’s article for the western alpine sheep sorrel is titled Rumex paucifolius, and it describes a perennial of moist mountain habitats from southwestern Canada to California and Colorado, so the plant BAMONA prints as pauciflorus is very likely the same one under its current spelling. No taxonomic authority was consulted to confirm the match, so the host plant is given here as BAMONA names it.

Mountain sorrel, according to Wikipedia, is a tufted perennial 10 to 30 cm tall with reddish stems and kidney-shaped leaves, found in alpine meadows, scree, snow-bed sites and beside streams, in wet places protected by snow in winter. That fits the cool, damp hollows where the copper is found. Females lay eggs singly on or near host plant leaves, the caterpillars eat the leaves, and half-grown caterpillars hibernate, so winter is passed as a caterpillar rather than as an egg, pupa or adult.

Flight season and adult food

One flight, June to August (BAMONA). Wikipedia puts it from mid-June to July or August, which reads as the same flight, described with a narrower peak. Adults feed on flower nectar. Wikipedia names thistles (Cirsium), alfalfa (Medicago sativa) and sweet clover (Melilotus) as nectar sources. The season is short, and the sources give dates for the species as a whole, not for any single mountain.

Status

BAMONA gives the Nature Conservancy global rank G5, demonstrably secure globally, with the caution that it may be quite rare in parts of its range, especially at the edges. Conservation is “not usually required” and management needs are “none reported.” Wikipedia, citing NatureServe, labels the species Apparently Secure and lists two subspecies, L. c. snowi and L. c. henryae. The two ratings differ by one step and the sources do not explain why; either way, no source consulted lists the species under a protection law.

A garden angle, with limits

Most species on this site sit comfortably next to a butterfly border. This one does not. It belongs to alpine and montane country, and none of the sources describes anyone raising it or luring it into a planted garden. What they do support is narrower: a gardener who lives inside its range, at elevation, near damp open ground where wild sorrel already grows, can leave those plants alone, keep the area free of pesticide sprays, and let thistles and clovers flower in July. That is protection of what is already there, not a planting scheme.

Farther from the mountains, the general advice in the butterfly garden guide applies to other species, with the nectar-plus-host rule at its core. For comparison with another small western butterfly that depends on one family of host plants, see the account of Moss’ Elfin, whose caterpillars eat stonecrops, and for an orange butterfly that does use sunflowers, the Gorgone Checkerspot.