Your admiral is actually a viceroy; (Limenitis archippus archippus); not
a white admiral. It’s an understandable mistake; since caterpillars and life
histories of the two are very similar; but, the yellowish-greenish cast of the
fifth instar viceroy caterpillars coupled with the protrusions at the base of the thoracic horns serve to differentiate the two species.

Also, the most common species in the Western U.S. is shared between the lorquin’s admiral (Limenitis lorquini) and the weidemeyer’s admiral Limenitis weidemeyeri . The western white admiral, Limenitis arthemis rubrofasciata barely enters into the U.S. through Northern Montana, North Dakota, and possibly Minnesota where intergrades between it and nominotypical L. arthemis may occur.

For more information about how to rear varying Limenitis taxa, click
here.
Thx, Todd

http://www.raisingbutterflies.org