Nymphalis [Aglais] milberti
Milbert’s Tortoiseshell

Family Description:
Alternate Common Name:
Fire-Rim Tortoiseshell.
Caterpillar: The caterpillar is black on top with a yellow stripe, green on the sides, speckled with whitish dots, and dotted with spines.
Adult: The butterfly has a wingspan of 1 to 2 inches. The upperside is dark brown to black, the sides edged with three stripes in this order: yellow, orange and black. Bluish dots may be present in the black edge stripe on the hindwings. There are two orange spots in the dark brown area of the forewings. Underneath, the wings are mottled dark brown edged with light brown.

This species occurs in southern Alaska, throughout the southern half of Canada and northern half of the U.S, and south to the Mexican border in the western third of the U.S. It occurs widely throughout Idaho.

These butterflies can be found in any environment but tend to be where it is cool, such as in woodlands or at higher elevations.


Caterpillar: Caterpillars feed on the leaves of nettle (Urtica spp.).
Adult: Butterflies use flower nectar and occasionally sap for food.

Young caterpillars live together in web nests at the tops of nettle plants. Later they may live and feed independently in leaves wrapped up with silk. There can be one to three generations each summer, depending on the climate. Adults overwinter, often several together in a group, in a physiological state called diapause. When multiple generations occur during a given summer, only the adults of the last generation overwinter. Adults generally fly from June until winter and emerge in spring to fly again until June.

Males perch to wait for receptive females, typically from noon to early evening. Females lay hundreds of pale green eggs in groups on the undersides of nettle leaves.

Idaho Status: Unprotected nongame species.
Global Rank:

G5; populations are widespread, abundant, and secure.

Ferris, C. D. and F. M. Brown. (eds.) 1981. Butterflies of the Rocky Mountain States. Univ. of Oklahoma Press, Norman, Oklahoma, USA, 442 pp.

Opler, P. A., H. Pavulaan, and R. E. Stanford. 1995. Butterflies of North America. Jamestown, North Dakota, USA: Northern Prairie Wildlife Research Center Home Page. http://www.npwrc.usgs.gov/resource/distr/lepid/bflyusa/bflyusa.htm (Version 05Nov98).

Opler, P. A. and A. B.Wright. 1999. A Field Guide to the Western Butterflies.   Second Edition.  Peterson Field Guide Series. Houghton Mifflin Company, New York, New York, USA, 540 pp.

Pyle, R. M. 1981. National Audubon Society Field Guide to North American Butterflies. Alfred A. Knopf, Inc., New York, New York, USA, 924 pp.

Scott, J. A. 1986. The Butterflies of North America. Stanford University Press, Stanford, California, USA, 583 pp.

Stanford, R. E. and P. A. Opler. 1993. Atlas of Western U.S.A. Butterflies (Including Adjacent Parts of Canada and Mexico). Published by authors, Denver, Colorado, USA, 275 pp.