Houdini Fly

The Washington State Department of Agriculture (WSDA) has confirmed reports of Houdini fly (Cacoxenus indagator) in Washington State. The Houdini fly is a kleptoparasite. It does not attack mason bees directly, but lays its eggs on the pollen meant for the mason bee young. The Houdini fly maggots then emerge and consume the food before the mason bee larvae, which causes them to starve.

Houdini fly is believed to be permanently established in Washington. However, mason bee producers and home hobbyists can reduce the impact on managed mason bees, which in turn will also help wild mason bee populations, through good management practices.

Mason bees are native pollinators that are active for a short time in early spring. They are one of the few reliable pollinators during cool spring weather, which is important for many fruit crops for farmers and gardeners.

Video showing how the adult Houdini fly inflates its head, which it does in an effort to break through mason bee nest mud walls to escape. 

Here you can see an adult Houdini fly visiting mason bee tubes. 

• Harvest mason bee cocoons – Open mason bee nesting materials before they emerge in the spring and destroy Houdini fly maggots. 
• Control adult mason bee emergence – If you cannot open nesting materials, place your nesting materials in a fine mesh bag and close tightly. As the bees emerge, release the mason bees daily and kill any Houdini flies. 
• Only use nesting materials that allow you to open, inspect, and harvest cocoons. Visual inspections can greatly reduce Houdini fly populations. 
• Only purchase pest-free mason bee cocoons. Before purchasing mason bees, ask the provider how they harvested and whether they inspected the cocoons for Houdini fly.

Crown Bees has provided the following video about Houdini Fly. The video includes information about how to manage Houdini fly in your own mason bee nesting materials. 

Houdini fly pest alert - Feb 2020 [PDF]

Questions? Contact us at pollinators@agr.wa.gov or 1-800-443-6684.