Un-bee-lievable Find on Mt. Tamalpais: A Rare Bee Lost For Decades

By Science Communication Specialist Michela Gentile, Golden Gate National Parks Conservancy

This photo is one of the first images ever taken of the San Francisco leaf-cutter bee (Trachusa gummifera) in its entirety. The bee had not been seen for decades before One Tam’s community science program found it in Marin County in 2024. This photo was taken by a professional biologist. Wildlife monitoring is conducted with appropriate training and handling under agency permits.

© Sara Leon Guerrero/Parks Conservancy

September 2024 - Leaf-cutter ants may get all the nature documentary attention, but have you ever seen a leaf-cutter bee? They are no less amazing, tidily snipping pieces of leaves or petals and using them, sometimes along with tree resin, to build their uniquely shaped burrows. Plus, leaf-cutter bees are important pollinators of many plants. The Bay Area is home to an endemic leaf-cutter bee species—the San Francisco leaf-cutter bee (Trachusa gummifera). But no one had recorded this special status species since 1980—until now!

The San Francisco leaf-cutter bee didn’t turn up in our initial surveys to inventory Marin County’s native bees. Sara Leon Guerrero, community science program manager at the Parks Conservancy and leader of the Tamalpais Bee Lab, designed a new community science project to try to find it—a search party! Sara and colleagues were scouting sites for the search earlier this year when she unexpectedly came across a bee that fit the description. Through her photographs, the U.S. Department of Agriculture confirmed it was indeed a male T. gummifera.

Finding the San Francisco leaf-cutter bee is good news in a time when scientists are documenting biodiversity loss due to climate change, habitat loss, and other stressors. It gives us hope that other species may still be found. It also underscores the importance of community science and local survey efforts. The sighting wouldn’t have happened without our One Tam partnerships’ collaborative Peak Health effort to check on the wellbeing of the Mt. Tamalpais region. It was the Peak Health project that identified bees as an important knowledge gap and inspired the formation of the Tamalpais Bee Lab to address it.

There’s still more to learn about this special species, and we’re working with the California Department of Fish and Wildlife to obtain the permits necessary to continue investigating. There will also be opportunities for community scientists to help! Stay tuned at onetam.org/tamalpais-bee-lab

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