A rare species of sand-loving bees is making a comeback in San Francisco's Presidio for the first time in about a century.
Ecologists spotted hundreds of silver digger bees in the park last week while surveying a dune restoration project in the park.
Experts believe the removal of invasive plants and the restoration of dunes and grasses at the former military base helped bring back the bees. They said the bees were common in San Francisco as late as the 1920s but began to disappear when the coastal prairie on the western side of the city was paved over for development.
"I said you have to look at this because I have never see this type of bee before," said Jonathan Young, a wildlife ecologist at The Presidio Trust.
Natural Resource Manager Brian Hildebridle was the one who made the discovery last week. He was checking the area for yellow jackets and poison oak for volunteers who were working on a restored dune on the western side of the Presidio.
Hildebridle and Young sent a photo of the bee to an expert who confirmed it to be a silver digger, a bee species which need dunes that are clean and healthy to reproduce.
Their habitat has been slowly restored since the military in 1994 turned the land over to the National Park Service.
Crews and volunteers have been working to restore dunes the city paved over, remove invasive plants that take over the sand and replace them with plants native to the area. The work is part of an 18-year restoration project.
"This particular bee is an indicator of good health. It's here. We’re trying to increase the biodiversity around the Presidio and this species' presence kind of tells us we’re doing a good job," Hildebridle said.