By Ryder W. Miller

The Presidio Trust, which is responsible for managing the Presidio National Park, has announced the successful re-introduction of the Checkerspot Butterfly (Euphydryas editha bayensis), which has been successfully translocated from San Bruno Mountain to the Presidio.

The butterfly is a federally threatened species that almost disappeared in the City.

“Yes, after two years of larvae translocations from San Bruno Mountain we have been seeing a lot of breeding occurring the park and lots of Presidio-born caterpillars. All signs of a successfully establishing population,” said Jonathan Young, a wildlife ecologist for

 The Checkerspot Butterfly
has been successfully re-introduced
at the Presidio. Courtesy photo.

the Presidio Trust. “Checkerspots were on the verge of blinking out in the city of San Francisco. They are lazy flyers and would never be able to come back to the Presidio on their own from nearby populations.”

Caterpillars were released at two sites in the Presidio: the Western Presidio Hills, located behind the Landmark Apartments at 15th Avenue and Lake Street, and eastern El Polin Springs, the valley below Inspiration Point near the Arguello Boulevard entrance to the park.  The butterflies have since spread out to other nearby areas, including Lobos Creek Valley.

Though they will not be flying through the Presidio again until next spring, butterflies were observed during the annual San Francisco butterfly count.

“Their flight season is over for the year, but all of the caterpillars born this spring will continue to feed on their host plants throughout the remainder of the year before emerging as flying adults next spring,” Young said.

He cautioned butterfly watchers use caution when trying to spy the flying insects.

“Most of these areas have accessible trails, but remember to stay on trails as these sites are very sensitive habitats and also have poison oak,” Young said.

Liam O’Brien, organizer of the San Francisco Butterfly Count, said he was proud that the conservation ideas he and others had years back fell on the right ears.

“Jon Young and the Presidio Trust have organized many folks to create a smooth transition between the translocated larvae and the ones that fly there now,” O’Brien said.

For more information about the Checkerspot Butterflies, and where they might be visible, Young recommends an app from iNaturalist.org.

In related news, Green Hairstreak Butterflies, which have a wildlife corridor project in the west side of the City, are rebounding in their Sunset District and Golden Gate Heights’ strongholds.

“The bar was slightly lower a decade back just creating new satellite habitat. The Hairstreaks showed up and they continue to show up,” O’Brien said.

Young added that there are a couple of Green and some Gray Hairstreaks that fly in the Presidio and around the City. The Green is less common and appears to be thriving in the Presidio. This year, butterfly counters observed a high number of them and found a few a new sites where they have never been seen before. Presidio Trust workers are also working to create new and improved wildlife corridors throughout the park.

“Connectivity between patches of habitat is very important for the longevity of wildlife. Presidio corridors are designed and managed to maximize connectivity for all wildlife, big and small,” Young said.

Expected later this year will be some butterfly migrations through the west side of the city. The Monarch butterfly migrates along the west coast and will winter in San Francisco if the weather is suitable. They usually arrive en masse in November. Rob Hill in the Presidio is a good place to see them “clustering” in trees by the hundreds.

Also visible will be California Tortoiseshell Butter flies, which over the last two years have had numbers in the thousands. They are sometimes mistaken for Monarchs.

Young recommends sharing observations of nature through the iNaturalist website (www.inaturalist.org).

“Researchers and managers, such as myself, see everything submitted on the site. The more eyes on the ground recording what they see helps us better track our biodiversity. Maybe someone will see a butterfly that hasn’t flown in the county in over a century … share it with the world. Even if you can’t identify it, the online community will if you get a decent enough picture,” advised Young.

The public can also get involved by planting butterfly-friendly plants in their backyards and volunteering to help with habitat restoration.

Young pointed out that “although the Presidio is home to a relatively large diversity of butterflies (about 25 species), there are a number of butterfly species that used to fly in the Presidio that no longer do so.”

One proposed reintroduction is the California Ringlet, a grassland-specific butterfly that was last seen in the Presidio more than 10 years ago.

The Xerces Blue butterfly is the first documented butterfly to go extinct due to human activities.

That event occurred in San Francisco in the ’40s.