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How to harvest and clean mason bee cocoons

Mason bee cocoons

Non-parasitized mason bee cocoons will be firm to the touch and dark grey. Cocoons that are lighter in colour and “crispy” to the touch are likely full of tiny parasitic wasps. You may even see the entry hole. One infested cocoon can contain up to 60 developing wasps! (Photo: Steph L via Flickr)

Cleaning wild baby bee cocoons sounds weird, if not invasive. But if you choose to attract these pollinators, take responsibility for increasing the likelihood of healthy bees emerging in spring.

It’s a lot like washing and maintaining bird feeders, baths and houses to help keep songbirds and hummingbirds healthy.

When to clean cocoons

The best time of year to clean bee cocoons is between October and December. The bees will be fully formed by then.

The goal is to reduce bee mortality and have healthy cocoons to release in spring! Cleaning cocoons keeps parasite numbers low and prevents disease spread in the colony. Washing cocoons and the bee house removes pollen mites, parasitic wasps, dermestid beetles and fungal pathogens that feed on pollen, nectar and developing bees.

Instructions for cleaning

You’ll need:

  • Scrap paper or newspaper
  • Scissors
  • Chopstick/stir stick
  • Glass measuring jug
  • Room temperature water
  • Spoon
  • Oxygen bleach
  • Sieve
  • Paper towel or reuse tissue paper
  • Clear plastic lid
  • Flashlight
  • Jar with lid (and punched holes)
  • Small paper box and tissue paper
  • Scrub brush

1. Prepare work area

Cover your work area with scrap paper to collect debris like mud and bee poop. Remove all plastic or wood trays from the bee house.

2. Check your bee house and tubes

Look for holes in the tube or if mud at the entrance has been compromised (see 5 below). Put suspect cocoons to the side. Mark or make note of the front and back end of tubes. Females are in the deeper chambers (more than three inches from the nesting hole). Males occupy the outer chambers (emerging first in spring). It’s possible to get an idea of male to female ratio by noting their size and location in the tube. Typical ratio is 2:1 male to female.

3. Open trays and tubes

Gently open plastic trays or cut homemade paper tubes (use scissors or remove tape). For houses made with reusable paper straws try using a dowel. Carefully pry cocoons (small brown ovals between mud walls) off with a chopstick or stir stick and set them aside. Inside are fully developed hibernating bees!

4. Identify contents

Carefully separate cocoons from other contents. You may find:

  • Black: gnat-sized, parasitic chalcid wasp
  • Bright yellow: pollen mite poop or frass
  • Brown/black: poop
  • Cream: dermestid beetle larvae that eat hibernating bees
  • Crescent-shape: mummified larvae infected with deadly chalkbrood fungus (dark and abnormal looking)
  • Dark grey: cocoons (males are often smaller; females are larger)
  • Grey: mud (it can take a bee 12 mouthfuls of mud to create one cell wall!)
  • Orange or reddish “sand”: pollen mites (e.g., Chaetodactylus krombeini) that eat what the bees need
  • White: mould
  • Yellow: pollen

Check images from Crown Bees and Oregon State University to help.

5. Identify “suspicious” cocoons

Non-parasitized mason bee cocoons will be firm to the touch and dark grey. Keep these. Go back to the tubes/tray you sorted. Cocoons that are lighter in colour and “crispy” to the touch are likely full of tiny parasitic wasps. One infested cocoon can contain up to 60 developing wasps! (Many gardeners attract parasitic wasps to combat garden pests. Consider adding parasitized cocoons to your bug hotel.)

Not sure? Spread the cocoons on a clear surface (bottom of a glass jar or on a clear plastic lid). In a dark room, shine a flashlight underneath and discard those that look hollow.

6. Wash viable cocoons

Place cocoons in jug of room temperature water. (They’re buoyant and water repellent.)

Agitate by stirring with your hand to loosen stuck on dirt, feces and mites. Debris will fall to the bottom. Scoop cocoons with a sieve and place in a bowl or pail of five per cent oxygen bleach solution. Soak for five to15 minutes, stir and then scoop them up with the sieve. Rinse them well to remove all traces of oxygen bleach. Do not use soap or detergent — that will kill the bees! Place washed bees on a cloth or paper towel to dry for about an hour.

7. Bee cocoon winter storage

Add clean cocoons to a small paper box wrapped with paper towel. Place the box inside a plastic yogurt container or glass jar — whatever will keep rodents and moisture out. Punch air holes in the lid. Store your container in the fridge at 0 to 5 C (60 to 70 per cent humidity), in an unheated garage or outside. Ants, woodpeckers, squirrels, racoons and bears can wipe out mason bee colonies. They’re more likely to survive the winter if you eliminate this risk!

8. Clean the house

Bees prefer clean nests! Soak trays in soapy water, scrub them with a brush and rinse thoroughly. Soak again in a five per cent oxygen bleach solution to kill bacteria and fungi. Spray the entire bee house with five per cent oxygen bleach, rinse well and dry. Store the house until next spring before you hang it.

Want to know more?

Get a copy of Margriet Dogterom’s Pollination with Mason Bees or visit BeeDiverse.