North America's Smallest Butterfly Now Calls Presidio Home

Presidio of San Francisco (September 15, 2008) — Score one for habitat restoration. The restored Crissy Field Marsh is now home to North America’s smallest butterfly. The Western Pygmy Blue was discovered last month during a butterfly survey of the Presidio, the first time the species has been spotted in the park.

The Western Pygmy Blue is actually fairly common, though easily overlooked because they often grow to no more than a half-inch (1.3 centimeters) in length. They are typically found in salt marshes around San Francisco Bay, but until now the only sightings in San Francisco had been in the southeastern part of the city. The butterfly’s larvae hatch into caterpillars that feed on pickleweed and the endangered California sea blite, which itself was introduced to the marsh when the National Park Service and Golden Gate National Parks Conservancy restored Crissy Field in 2001.

The Crissy Field Marsh is a prime example of a successful salt marsh restoration project. Since its completion seven years ago, dozens of species of birds, fish and invertebrates that have been absent from the Presidio for decades have been returning to the area.

Native habitats are being restored in many areas throughout the Presidio. As part of the Presidio Trust’s environmental remediation program, an Army-era landfill was removed and a creek was “daylighted” in the Tennessee Hollow watershed. The number of nesting birds has since increased dramatically, and stickleback fish are now seen swimming in the creek. Over the course of a seven-month study in the Presidio, researchers observed 57 species of bees. The highest number of rare species was observed in the remnant native habitats of the park, suggesting that insect diversity can be a benchmark of the long-term success of natural restoration projects. Habitat restoration projects are also underway at Mountain Lake, Inspiration Point, on the western coastal bluffs, and elsewhere.

The Presidio’s natural resource efforts are a partnership of the Presidio Trust, the Golden Gate National Parks Conservancy (GGNPC), and the National Park Service (NPS).