San Emigdio Blue Butterfly

Plebejus emigdionis

  • Petitioned for Sensitive Species Listing – U.S. Forest Service

Image courtesy Bill Bouton

The San Emigdio blue butterfly (Plebejus emigdionis) is a unique species found only in Southern California including the Mt. Pinos Ranger District of Los Padres National Forest. It is unique in that females will only lay their eggs on three different species of saltbush when a particular species of ant (Fomica pilicornis) is present. The ant protects the caterpillars from being eaten by other ants and wasps, and in return, the caterpillar secretes sugar and amino acids for the ant to eat.


But even with these personal bodyguards, the species is struggling. Activities threatening the survival of this species include water diversion, off-road vehicle trespass, livestock grazing, vegetation clearing, land development, road work, and spread of invasive species. As a result of these many threats, San Emigdio butterfly populations are predicted to decrease 50-70% in the long-term.

Because of the species’ dire status, several national forests have listed this butterfly as a sensitive species, yet the Los Padres Forest Service has not listed them as such on the grounds that it is not occurring within the Los Padres.

Image courtesy David Horner, SolarDarkroom Photography.

Photo courtesy David Horner, SolarDarkroom Photography.


In 2014, ForestWatch submitted a request to the U.S. Forest Service to list the San Emigdio blue butterfly as a “Sensitive Species.” There is no timeline for when the Forest Service has to decide if the species deserves sensitive listing, but without the proper conservation procedure in place, we risk significant decreases that may warrant its listing as endangered. Thus, it is critical to provide the San Emigdio blue with protections afforded by placement on the sensitive species list before federal actions threaten the viability of this species further. The addition of the this butterfly to the “Los Padres National Forest Sensitive Species List” would help protect San Emigidio blue populations in the forest by confirming that any potential impacts to the butterflies or their habitat are evaluated and mitigated. It would also ensure the utilization of the best and most current information to inform land management decisions throughout the region.