San Emigdio Blue Butterfly

Plebejus emigdionis

  • Sensitive – U.S. Forest Service (2020)
  • G1 Critically Imperiled – NatureServe (2012)
Photo courtesy David Horner, SolarDarkroom Photography

The San Emigdio blue butterfly (Plebejus emigdionis) is a unique species found only in central and 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.

Threats

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, the Forest Service has granted special protections to San Emigdio blues in three national forests: Los Padres, Inyo, and San Bernardino.

Image courtesy David Horner, SolarDarkroom Photography.
Photo courtesy Bill Bouton

Conservation

In 2014, ForestWatch submitted a request to the Forest Service to list the San Emigdio blue butterfly as a “Sensitive Species” in the Los Padres National Forest. Placement on the sensitive species list will help address threats facing the species and prevent further declines. The addition of this butterfly to the Los Padres National Forest sensitive species list will 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 will also ensure the utilization of the best and most current information to inform land management decisions throughout the region.

In 2015, ForestWatch conducted a survey of San Emigdio Blues in the Mt. Pinos Ranger District, accompanied by Forest Service representatives and two butterfly experts. We recorded several occurrences of San Emigdio Blues, confirming that the butterfly occurs in the Los Padres. Additional locations inside the forest boundary were recorded in 2019.

In 2020, six years after we submitted our request to the agency, we received an updated Sensitive Species list for the Los Padres National Forest that included the San Emigdio blue butterfly. The species now has enhanced protections where it is found in the national forest.