Solitary Bees

How to Protect Your Mason Bees from the Houdini Fly

Mason bees are a welcomed pollinator to any garden. So much so, that many people enjoy installing mason bee houses in hopes of attracting mason bees to their homes.

Recently, a parasitic fly has been damaging mason bee populations. This fly is called the Houdini fly. Luckily, if we take the proper precautions and properly care for our mason bee houses and coccoons, we can help to protect mason bees from the Houdini fly.

Disclosure: As an Amazon Associate I earn from qualifying purchases. This is at no cost to you and helps to keep this website running.

What is the Houdini Fly?

The Houdini fly is well known in Europe, and has recently made it’s way to the United States. It is called the Houdini fly for the way it is able to escape mason bee nests. Other names of this fly are devil fly, or red devil, because of it’s large red eyes.

Houdini flies are from the same family as the fruit fly, and are also classified as kleptoparasites. This means that they steal the food of another animal. In this case, it is the food of young mason bees.

How Does the Houdini Fly Harm Mason Bees?

Houdini flies harm mason bees by entering the mason bee tube and laying eggs on the pollen that is meant for the emerging mason bee. Once the Houdini fly maggot emerges, it consumes the pollen before the mason bee larvae hatches. This causes the mason bee to starve and die.

Signs of Houdini Fly Infestation

The most obvious sign of Houdini fly infestation is the presence of clusters of small, white maggots in the mason bee nest cell. At this point, you may notice that the mason bee larvae is dead or missing all together.

Preventing Houdini Flies

It is not believed that Houdini flies can be fully eradicated, however, there are things you can do to prevent Houdini fly infestation.

  • Use a mason bee house that opens so you can visually inspect your nesting materials.
  • If you are unable to inspect your nesting materials, place them in a fine mesh bag. Release the mason bees when they emerge, and kill any flies.
  • Thoroughly clean all nesting blocks every year.
  • Harvest mason bee cocoons before they emerge in Spring.
  • When harvesting cocoons, destroy any Houdini fly maggots you find.
  • Purchase mason bee cocoons from places that inspect for Houdini flies.

Recommended Mason Bee Houses

The following mason bee houses work well for Houdini fly prevention because they open up for visual inspections.


The Houdini fly is a parasite of the mason bee. It lays eggs in the mason bee tube and consumes all the pollen before the mason bee larvae hatches. The best way to prevent Houdini fly infestation is by doing visual inspections for fly maggots and harvesting mason bee cocoons before they emerge in spring.