Harvesting Mason Bee Cocoons

IMG_6860By late September, mason bees have completed their development and are safely ensconced in their cocoons awaiting the return of spring. It’s a good idea to now extract the individual cocoons and store them in a safe and temperature-stable location. This keeps them away from birds and other predators. But more importantly, it helps to limit spread of disease. As you inspect the cocoons, you can cull those that are dead or diseased; and when the bees hatch, they don’t have to burrow their way through the potentially infectious detritus.

Harvesting is very easy. The cocoons are surprisingly tough, despite their delicate appearance. They can withstand some handling, and even brief submersion in water. Last year I cleaned the cocoons by tossing them with sand. Since then I’ve learned that there isn’t any real benefit to this procedure. So after picking out the duds I simply place the viable cocoons in a cardboard box and store them in a cool and dry place.


These plastic trays were well accepted by the bees. Each tube can hold about 8 cocoons. Wasps did manage to get at a few of them, which did not happen in the wood blocks. You can also see a few instance of pollen mite infestation: instead of a cocoon there’s just a mass or orange mite feces.




This cocoon was targeted by the parasitic ‘mono’ wasp. It lays its eggs on the bee larva. In the end, you have a cocoon full of baby wasps.






I’m not sure what happened to this bee. Hopefully it is not a case of chalkbrood. Chalkbrood is a fungal disease that can quickly wipe out an entire colony of bees.






My DIY woodblock houses worked very well. The paper tubes only hold about 4 cocoons. But it’s cheap and easy to make lots of these from wood scraps.

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6 Responses to Harvesting Mason Bee Cocoons

  1. Dan Plaster says:

    Boy, that second to last photo does look similar to that link you posted to chalkbrood

  2. Paul B says:

    If you are getting an average of four cocoons in your home made drill block it may be down to the depth of the tunnels. If it’s less than four inches you may also be getting predominantly male bees and thus your nesting females are working. Can you distinguish the difference between larger female cocoons and the male ones?

    • Yes, I need to get a longer drill bit and make better blocks. The difference between males and females is pretty obvious – I’ll have to look more closely when I harvest my remaining blocks and figure out what my ratio of males to females is.

      What do you mean by ‘nesting females are working’? I think the males’ role is only to fertilize and they don’t contribute anything to nest-building.

      • Paul B says:

        Very sorry that was a distracted editing omission – I was trying to say something like ‘females are working very hard for their/your population to stand still’.
        If they are too short (I found this with 4 inch lined drill blocks) you may end up with one or no females being laid at the end of the tunnel, which is then compounded by losses due to parasites (mites, flies and perhaps chalcid wasps) and spring dispersal.
        ..and yes it’s good to keep a record of your numbers and ratios to be able to judge how well you are doing and figure out adjustments – nest cleaning can become a sort of forensic science.

  3. I’m not an expert on mason bees, so I really enjoyed this post!

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