Synonyms and other taxonomic changes
Papilio bairdii W. H. Edwards 1866. Type locality: nr. Prescott, Arizona - This name was applied to the black form.
Papilio brucei W. H. Edwards 1895. Type locality: Roaring Forks, Colorado - This name was applied to the yellow form.
Papilio hollandi W. H. Edwards 1892. Type locality: Glenwood Springs, Colorado - This name was applied to individuals intermediate to the black and yellow forms.
Black forms are very like P. polyxenes, and are sometimes difficult to separate. Generally yellow spots above (if present) are more "fuzzy" on the inner edge, and they contain less orange on the under side. The black "pupil" of the orange spot at the angle inside of the tails on the hind wing is elongate and connected to the black edge of the wing (in P. polyxenes it is usually round and centered, particularly on the upper side of the wing). The "tegulae" (little flaps on the thorax above the base of the front wings) are usually yellow in P. bairdii and mostly black on P. polyxenes. Also, the larval host for P. bairdii is usually Artemisia (though they will use some Umbellifers such as Fennel, and sometimes Rutaceae such as Rue). The larval hosts for P. polyxenes are Umbellifers, or in the southwest some shrubby Rutaceae (also Rue in gardens).
Yellow forms are like subspecies oregonius, but with black areas a bit more extensive. They differ from P. zelicaon usually in larger size, more elongated forwings, more extensive yellow markings (especially below), with the black pupil usually connected and not so large and rounded (usually not connected, or at least large and round in P. zelicaon). The tails are usually longer and often more curved. The body is more prevalently yellow, with black lines below (in P. zelicaon mostly black with yellow markings, with only sides of abdomen yellow).
California east to Colorado, New Mexico & Wyoming, perhaps into northern Chihuahua and Sonora. Blends with ssp. oregonius in northern Great Basin and in Rockies. Blends with ssp. dodi at the west margin of the Great Plains. The area where ssp. bairdii becomes ssp. dodi is debated (some consider dodi to be the same as bairdii). The areas of transition from one subspecies to another in the U.S. are ill-defined, and are hard to define meaningfully on a map.
Black forms tend to dominate in the south (s. Utah, s. & e. Colorado, Arizona, New Mexico, sw. Nebraska, etc.), while yellow forms prevail northward.