UC Davis entomologist Leslie Saul-Gershenz lent her expertise when a volunteer discovered what turned out to be "long-lost" silver digger bees in restored sand dunes at the San Francisco Presidio, a former military post now owned and operated by the National Park Service.

No large aggregations of the species had been seen in that area for nearly a century.

Saul-Gershenz confirmed that the digger bees are Habropoda miserabilis and were probably common in the sandy dunes of that area as late as the 1920s. When non-native ivy, eucalyptus and ice plants took over their habitat, the bees disappeared.

“The discovery of a thriving native bee colony on the western side of the Presidio is the latest example of how the removal of invasive plants and the restoration of dunes and grasses at the former military base have helped bring back coastal habitat that thrived in San Francisco for tens of thousands of years before the city was built,” said Saul-Gershenz, who received her doctorate in entomology from UC Davis and is now associate director of research for the Wild Energy Initiative, John Muir Institute of the Environment, on campus.

“I am very happy to see this nest site at the Presidio,” said Saul-Gerzhenz, who has worked on the biology, chemical ecology and parasite interactions of this group of bees in the genus Habropoda for many years. She has researched Habropoda at other sites, including the Oregon coast and the Mojave desert.

“This nest parasite M. franciscanus was originally described from the dunes in San Francisco near Lake Merced by Van Dyke in 1928,” Saul-Gershenz said. “It is presumed to be locally extirpated in San Francisco due to habitat alteration. However its host bee, H. miserabilis  appears to have finally found a suitable nest location in a sand dune area being restored by the Presidio Trust in the Presidio National Park.  The resiliency of nature provides hope for the future.”

In a news story published in the San Francisco Chronicle on March 29, reporter Peter Fimrite quoted the UC Davis entomologist as saying that the silver digger bees were “all but gone” by the mid-20th century. Since 1960, only a couple of specimens have been found at the Presidio. Saul-Gershenz collected a digger bee specimen near Baker Beach in 1998, but no large aggregations have been found--until now.

"Biologists have reported a more than tenfold increase in the number of native plants in the Presidio, including at least four that are federally listed endangered or threatened, among them the Presidio clarkia," wrote Fimrite. "The Franciscan manzanita, which was believed to be extinct in the wild, was discovered in the Presidio in 2009. It was the first of its kind seen in its native San Francisco since the old Laurel Hill Cemetery was bulldozed in 1947 and paved over for homes."

Silver digger bees "have made a comeback, after being nearly wiped out, in several other areas in California, including Bodega Marine Reserve in Bodega Bay and Lanphere Dunes in the Humboldt Bay National Wildlife Refuge after both places were restored," Fimrite related.

Brian Hildebidle, stewardship coordinator for the Presidio Trust, discovered the colonies while surveying a dune restoration project.  Jonathan Young, wildlife ecologist for the Presidio Trust, was also featured in the news story.

Gershenz and collaborator Jocelyn Millar of UC Riverside and others deciphered the sex attraction of Habropoda miserabilis and the deceptive mimicking blend used by its nest parasite Meloe franciscanus working with a population on the coast of Oregon (Saul-Gershenz et al. 2018). They documented a new parasite-host location system while conducting research on related species in the same genus Habropoda pallida found in the Mojave and Sonoran Desert (Saul-Gershenz and Millar 2006).