Papilio polyxenes coloro
Desert Black Swallowtail
This denizen of the desert is closely related to Papilio zelicaon and easily confused with that species. One key difference is habitat: coloro is expected in the deserts and prefers turpentine broom (Thamnosma montanan) as the host. The anise swallowtail prefers cooler climes and will use fennel, as well as other carrot family plants. Either species may use Tauschia arguta or something similar in a pinch. Where they do overlap, they can usually be told apart through differences mentioned on the zelicaon page.
The desert black is an avid hilltopper. It can also be common in desert environs in favorable years where the host is present. For instance, in spring of 2020, this butterfly was very common in the Mojave National Preserve, whether atop Teutonia Peak, or anywhere else turpentine broom was growing. I even saw a couple of the black form clarki there for the first time.
This butterfly was first named as the equivalent of a subspecies by W.G. Wright in 1905. In a 1982 paper by C. Ferris and J.F. Emmel ("Discussion of Papilio coloro W.G. Wright (= Papilio rudkini F. & R. Chermock) and Papilio polyxenes Fabricius (PAPILIONIDAE)," Bulletin of the Allyn Museum, No. 76, pp. 1ff), the type locality was determined as Whitewater Hill in the Coachella Valley. That is just northwest of the intersection of Interstate 10 and highway 62 in an area now full of wind turbines.
A fresh Papilio polyxenes coloro perching along Cactus Spring Trail, April 27, 2017.
Here's a coloro nectaring on the same trail a week earlier, April 22, 2017.
A hungry last-instar coloro
larva was munching host Thamnosma montana
right at the trailhead on the same hike as above.
A closer look at the same caterpillar.
A very cooperative Papilio polyxenes coloro at gravel along Horsethief Creek, which is down Cactus Spring Trail in Riverside Co. September 20, 2014. This one didn't move for five minutes; not my usual experience with these. These can be very small, and this one looked not much larger than a Painted Lady.
This 'Desert' Black Swallowtail - Papilio polyxenes coloro - was hilltopping above Palm Springs. September 4, 2010.
Small, early stage caterpillar of Papilio polyxenes coloro
, probably a second instar, on host Thamnosma montana
. April 15, 2011, at the Cactus Springs Trail in the Santa Rosa Wilderness.
Another caterpillar of Papilio polyxenes coloro, probably a fourth instar. After this stage, the spines disappear and they become smooth - see the one above from 2017. April 30, 2019, again at Cactus Springs Trail in the Santa Rosa Wilderness.
I chased this black coloro all over the desert floor off Lanfair Road on the way to a hike in the New York Mountains in the Mojave National Preserve. John Comstock named the dark forms clarki and comstocki that pop up rarely in desert swallowtails, and this one would appear to be the former (no pun intended). Taxonomically, that means next to nothing; it's just a cool aberration.
William Greenwood Wright described this swallowtail in the 1905 book Butterflies of the West Coast. He personally collected the type, and many other of the butterflies in his book.