7. How to Harvest Bee Cocoons

Ensure Bee Health

7.1 Why Harvest Bee Cocoons

7.1 Why Harvest Bee Cocoons

Open your nesting materials to remove healthy bee cocoons, leaving pests and diseases behind, and improve your bee population.

Bamboo tubes and drilled blocks of wood are excellent habitats for pests and diseases, due to their inability to be opened and cleaned.

Wild and naturally occurring nesting holes are spread across the landscape. Unfortunately, man-made nesting holes are close together and it's easy for pests and diseases to spread. Bees will nest inside of infected nesting holes and they aren't able to clean their homes before moving in.

It's up to us to give bees healthy habitats. Open your nesting holes to harvest cocoons and provide fresh nesting holes each season. Harvesting cocoons is easy: just open the nesting holes, remove healthy bee cocoons, and leave pests and diseases behind.

  • Crown Bees nesting materials are designed to be easy to open to harvest cocoons.
  • Harvesting cocoons can be a little messy but it is well worth your time and effort.
  • Harvesting bee cocoons is a great teaching activity for family and friends.

Top reasons to harvest hole-nesting bee cocoons:

Parasitic Wasps

Parasitic Wasps - Gnat-sized Larvae Killers

Parasitic wasps are gnat-sized wasps that lay thier eggs inside bee larvae.

Dozens of adult wasps emerge from each infected bee cocoon and return to infect bee larvae the next pollination season. Harvest cocoons to reduce the attack from these sneaky pests.

Pollen Mites

Pollen Mites - Microscopic Pollen Thieves

Microscopic pollen mites eat the pollen loaf and starve the bee larvae.

Healthy bees must crawl through unopened nesting holes, spreading the mites to new flowers. Mites also walk to neighboring nesting holes.


Chalkbrood - Deadly Fungal Infection

Chalkbrood is a deadly fungal infection that is picked up by bees on flowers.

The bee larva consumes the spore, dies and becomes a mass of larva-shaped spores. Healthy bees walking through unopened nesting holes spread the spores throughout the nesting holes and to new flowers.

Houdini Fly Maggots

Houdini Fly Maggots -- Destructive Freeloading Grubs

Parasitic fruit fly eats pollen loaf and starve the bee larvae.

Houdini flies are kleptoparasites that eat the pollen loaf. Left alone, fly populations will continue to grow. Harvest cocoons or place nesting materials in a fine mesh bag to only allow adult mason bees out to control this emerging pest.

Left unchecked, these parasites and disease can kill your bee house population. All of these threats to solitary bees naturally exist in your garden. Chalkbrood and pollen mites are spread when healthy bees must walk through an unopened and infected nesting chamber. To minimize these problems, harvest your bee cocoons and provide fresh and clean nesting holes.

Houdini Fly - A new invasive pest threatens Mason Bees
Why harvest bee cocoons? Pests and Diseases

Pests & Diseases By the Numbers

From the outside, filled nesting holes can look clean and tidy. We opened a sampling of our reusable wood nesting trays gathered from various gardens here in the Pacific Northwest and found some startling results. The sampled 112-hole wood trays were clean at the beginning of the year. Here’s what we found when we opened the trays in the fall:


Tray A

Tray B

Tray C

Number of filled nesting holes out of 112




Pollen Mite filled cocoon chambers




Houdini fly filled cocoon chambers




Chalkbrood filled cocoon chambers




Mono wasp filled cocoon chambers




Corn Meal Moth filled cocoon chambers




Total cocoon chambers filled with pests




Percentage of pests




Healthy mason bee cocoons




Percentage of surviving bee cocoons




Total cocoon chambers including pests and diseases





These results are surprising and unfortunately, pests are opportunists that take advantage when the conditions are in their favor. If we leave the wood trays unopened and harvested cocoons 2-3 years from now, we predict that the number of bees that survived the pests and diseases would diminish significantly each year. The data from this table is the reason why we recommend harvesting cocoons each year so that your garden pollinators become and remain plentiful.

Topic Completion

Pests & Diseases

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