Rent Mason Bees Partners with UC Davis to Combat Rising Houdini Fly Threat to Native Bees

Join the Hunt for Houdini Flies!

BOTHELL, Wash., April 30, 2025 /PRNewswire/ -- Rent Mason Bees, the nation's largest solitary bee provider, has partnered with researchers at the University of California, Davis to address the alarming spread of the Houdini fly, an invasive kleptoparasite threatening native mason bee populations across the Pacific Northwest.

This week, they officially launched THE HOUDINI FLY HUNT, calling on bee hosts and citizen scientists nationwide to help track and report sightings of this destructive invader.

The collaboration is led by Abigail Lehner, a PhD candidate at UC Davis, who is researching how mason bees are impacted by global environmental change. Lehner recently received a grant from the Western Sustainable Agriculture Research and Education (WSARE) program to deepen the understanding of Houdini fly biology and to develop an effective management plan.

"I've seen a significant increase in Houdini flies in Washington and Oregon this year, and they are devastating to mason bee populations. Unmaintained bee hotels are a major cause of their spread," said Lehner.

The Houdini fly—a small, gray insect with red eyes, about the size of a fruit fly—was accidentally introduced from Europe within the last few years. These parasitic flies are often seen hovering near bee hotels or sitting at nest entrances.

Houdini flies exploit mason bees by sneaking into nests when the mother bee is away. They lay their eggs on the pollen stores intended for bee larvae. When the Houdini larvae hatch, they consume the pollen, starving the developing mason bees. Fully grown Houdini flies then escape the sealed chambers at the same time the surviving bees would normally emerge, earning their notorious name.

Thyra McKelvie, Managing Director of Rent Mason Bees, emphasizes that proper care and public education are critical.

"Many people don't realize that setting up a bee hotel comes with responsibility," McKelvie said. "Without proper maintenance, these hotels can quickly become breeding grounds for parasites like the Houdini fly."

McKelvie outlines three critical steps for responsible mason bee care:

1. Place clean, openable nesting material out in early spring.
2. Remove nesting materials at the end of spring (mason bees only live 6–8 weeks).
3. Harvest and clean cocoons in the fall to remove parasites.

"If you want to prevent further spread, it is imperative to clean out your bee hotel in the fall and remove Houdini larvae," Lehner added.

Join the Houdini Fly Hunt!

One of the best ways to combat this threat is by identifying where Houdini flies are spreading—and that's where you come in.

Report your findings here: Houdini Fly Hunt!
Watch the video to learn how to spot and stop Houdini flies: Mason Bee Predator Alert! Houdini Fly – How to Spot, Stop & Hunt!

Your participation is crucial in protecting our native pollinators and strengthening ecosystems across the country.

www.RentMasonBees.com

SOURCE Rent Mason Bees