Utah Lepidopterists' Society

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Utah Butterfly and Skipper Species' Descriptions

Papilio eurymedon  

(Pale Swallowtail)


Adults Top Row:  Male and female.  Bottom Row:  Male and female ventral surface. (Click on image for larger picture.) Mature larva (on hostplant Ceanothus velutinus)       Photo courtesy Tom Allen.

Example of habitat  Example of hostplant--Ceanothus velutinus 


        The Type Locality of Papilio eurymedon is "...été trouvée en Californie." (Queen Lily Campground, near Belden, North Fork Feather River, Plumas County, California, Lucas.)  

       Currently, there are no described subspecies although it is the opinion of this author that there are potentially three valid subspecies of this butterfly.  Utah colonies of P. eurymedon are somewhat distinct from cismontane California populations.  One of the distinguishing features is that Utah individuals tend to have more orange on the VHW than California adults.  At the same time, colonies of P. eurymedon in the Pacific Northwest tend to have much darker DFW black bands (or tiger stripes) than either Utah or California populations.  

        In "Butterflies of California," John Adams Comstock referred to this taxon as the mountain swallowtail or "Papilio eurymedon albanus" even though "albanus" was originally described as a low elevation California butterfly and falls as a junior synonym to "eurymedon."

Utah Distribution and Habitat:

        P. eurymedon flies roughly between the elevations of 6000' to 9500' in mountainous regions of the state that harbor colonies of its hostplant.  

Last instar P. eurymedon larva on leaf of hostplant Ceanothus velutinus. P. eurymedon pupae are normally earth tones; however, sometimes Northern Utah populations yield a green and chocolate brown appearance.


      In Northern Utah's Wasatch Front,  along with other butterflies and skippers like Nymphalis californica, Satyrium saepium provo, Incisalia augustinus annettae, and Erynnis pacuvius lilius, Papilio eurymedon utilizes the hostplant Ceanothus velutinus.  

     In the mountains of southern Utah, P. eurymedon likely uses other mountain lilacs such as   Ceanothus martinii and Ceanothus fendleriWhether or not this butterfly uses Ceanothus greggii in Washington County is not known (by the author.)

     Throughout Utah, the pale swallowtail is univoltine and overwinters as pupa.  In the lab, the approximate time from ova to pupa is 6 weeks--which is slightly longer than its machaon group counterparts.

     Lab rearing of P. eurymedon can be quite a challenge for three reasons.  The first reason is the relative difficulty of finding larvae on the hostplant out in the field.  On the average, within a colony, it takes roughly between one to several hours of diligent searching just to find 1 immature on the plant.  This is the case because of the sheer biomass of hostplant as compared to the numbers of immatures in a typical colony coupled with the fact that, unlike P. indra, females of P. eurymedon, in Northern Utah at least, do not seem to prefer to oviposit on certain sections or sizes of its hostplant.  As long as there is new leaf growth, P. eurymedon seems to oviposit arbitrarily anywhere on its host making the finding of the critters a true challenge.

      The second challenge of finding adults of P. eurymedon, let alone immatures, is the fact that  this butterfly usually is the least common of the three Utah glaucus-group swallowtails.  Furthermore, its numbers in northern Utah seem to have been diminishing between 1999 and the time this paper is being written (summer of 2004.)  The cause for this decline is probably more related to ova and larval parasitism than it is to drought.  (Look for pale swallowtails to recover towards the end of this decade.) 

      The third reason why rearing P. eurymedon can be quite a challenge is the difficulty of getting females to oviposit in the lab.   Unless your name is Jim Reiser, getting ova out of any glaucus-group swallowtail in the lab can be a real challenge.  

Todd Stout

All images of Limenitis weidemeyeri on the ULS Info Bar courtesy Jay Cossey                                                                    

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