Rocky Mountain Dotted-Blue (Euphilotes ancilla [Barnes and McDunnough])
Wing span: 5/8 - 1 inch (1.6 - 2.5 cm).
Identification: Upperside of male is deep blue with wide black borders; hindwing orange band usually absent. Female brown with variably expressed marginal orange patch on the hindwing. Underside of both sexes is light blue-gray with black spots. Underside of forewing often suffused with smoky gray.
Life history: Dotted Blues usually stay near their host plants. Males patrol around the host plants all day to find females. Eggs are laid singly on flowers or buds; caterpillars eat flowers and fruits and are tended by ants. Chrysalids hibernate in leaf litter.
Flight: One flight; late April to early August depending on location and elevation.
Caterpillar hosts: Various Eriogonum species, especially Sulphur-flower.
Adult food: Flower nectar, especially from Eriogonum.
Habitat: Sun-exposed rocky slopes and flats with host plant colonies.
Range: Washington south to California and southern Alberta and Saskatchewan south through rockies and high plains to Wyoming, Colorado, Utah, and northwestern New Mexico.
Conservation: Not required for the species, but rare subspecies in Nevada require survey and assessment of threats from alien weeds.
The Nature Conservancy Global Rank: G5 - Demonstrably secure globally, though it may be quite rare in parts of its range, especially at the periphery. Subspecies shieldsi Austin and purpura Austin of Nevada are of high conservation concern because of their local nature and possible threat from invasive alien weeds such as cheatgrass.
Management needs: Conserve habitats for rare subspecies and maintain host plant populations.
Emmel, T.C., editor. 1998. Systematics of Western North American Butterflies. Mariposa Press, Gainesville, Fla. 878 pp. Ferris, C.D. and F.M. Brown. 1981. Butterflies of the Rocky Mountain States. University of Oklahoma Press, Norman. 442 pages. Layberry, R.A., P.W. Hall, and J.D. Lafontaine. 1998. The Butterflies of Canada. University of Toronto Press, Toronto. 282 pages, 32 color plates. Opler, P.A. 1999. A field guide to western butterflies. Houghton-Mifflin Co., Boston, Mass. 540 pages, 44 color plates. Scott, J. A. 1986. The butterflies of North America. Stanford University Press, Stanford, Calif. 583 pages, 64 color plates. Stanford, R. E. and P. A. Opler. 1993. Atlas of western USA butterflies including adjacent parts of Canada and Mexico. Denver and Fort Collins, CO.
Author: Paul A. Opler
State and Regional References:
Brown, F.M., Eff, J.D., and B. Rotger. 1957. Colorado Butterflies. Denver Museum of Natural History, Denver. Ferris, C.D. and F.M. Brown. 1980. Butterflies of the Rocky Mountain States. University of Oklahoma Press. Norman. Layberry, R.A., Hall, P.W. & Lafontaine, D.J., 1998. The Butterflies of Canada. University of Toronto Press, Toronto, ON. 280 pp. Opler, Paul A. 1999. Peterson Field Guide to Western Butterflies, revised edition. Houghton Mifflin Co., Boston, Mass. Stanford, R.E. and P.A. Opler. 1993. Atlas of Western USA Butterflies. Privately published, Denver, Colo. Tilden, J.W. and A.C. Smith. 1986. A Field Guide to Western Butterflies. Houghton Mifflin Co., Boston, Mass.