Saturday, November 2, 2013

Cleaning Mason Bee Condos with Brian Campbell

 It's that time of the year to prepare your mason bees for winter by cleaning the cocoons and condos. Brian Campbell gave a thoroughly fascinating workshop on mason bees as part of the VanDusen Garden workshop series. Brian started the class with a talk on the diversity of bees in British Columbia. He says our province is a great place to practice native bee conservation. This talk is worth the price of admission alone and Brian can come to your garden club or school and tell you all about our local bees. He can give you the confidence to clean your mason bees and help them live to produce another generation next spring.

My father-in-law says he brings his houses in to dry a few days before he cleans them out. Brian takes his in much earlier to protect them from birds and predatory mites. If you had two condos you could try both methods and compare the results. (Note that it's important not to disturb the egg while it is developing into a larva.)

If you have houses made of drilled holes with paper tubes you need to pull out the tubes and unroll them to remove the cocoons. I recently read that parchment paper for cooking is the best paper for rolling your own tubes if you are using the system with the drilled holes.When cleaning cocoons it's important to watch for hibernating wasp queens. We had found one that appeared totally dormant until she woke up and began flying around the room. There are several other mason bee pests you may find in your tunnels including parasitic wasps, cuckoo bees, cuckoo wasps, carpet beetles, flour beetles, spider beetles and pollen mites.

Also look for any cocoons that are damaged and empty and put them in the garbage pile. If your tunnels are filled with crumbly brown matter and chalky white hard  dead larva you may have a condo infected with chalk brood. In this case you've got to quarantine your condo and clean it with water and bleach. Clean your hands as well to prevent the disease from spreading.

If you've got some healthy cocoons, separate them out and wash them in a tub. Some people use bleach, and some don't. There are other people experimenting with natural oils to eliminate the mites and also the cleansing action of gentle abrasion with sand. There are natural eco-sensitive bleaches on the market that would work for this. Brian assures us the healthy cocoons are water proof and the bleach will not get into the bees.

 This condo was interesting because it contained the cells and larva of resin bees. If these are put back together once the mason bees are cleaned out they should pupate and hatch next summer. The exact species of this bee remains a mystery to us. I really wish we had a digital microscope to look more closely at all the insects and debris in the tunnels. (If anyone knows of a good digital microscope for classroom and home use with a MAC OS, please let me know. Price is an object, BTW!)

 It's as simple as this: just putting the cocoons in water and letting them float to the top. You can remove them and let them dry on an old towel. Some people repeat this three times or also use sand to help abrade debris from the cocoons. The most common debris is black pellets of bee poop and pollen mites. These hairy footed mites hitchhike on the backs of bees to eat pollen. Like Varroa mites they reproduce at an alarming rate which can all end in tears. If hairy mites in the tunnels run out of pollen they eat the mason bee cocoons and then they eat the mason bees.

Next you can "candle" the bees by laying them on a powerful flashlight or light tray. Brian encouraged us to keep track of how many large (female) cocoons and smaller (male) cocoons were intact. By mid December (or earlier) puts the cocoons in a plastic bag in a jar in the refrigerator until spring. He adds a wet piece of paper towel on the bottom to keep some humidity in the jar, but not too much. Check your bees periodically to see if they are too dry or too wet.

We also found a tiny dead cuckoo wasp: Pseudomalus auratus. It was just a few mm long and it had a shiny turquoise thorax and a red shiny abdomen. It is one of the wasps that parasitizes mason bees. This wasp does not sting, but curls into a ball when it feels threatened. Awwww.

Should you clean your cocoons? Yes. Most folks had not cleaned their condos for a couple of years and they were overrun with pollen mites and disease. From my research I also learned it is best to buy cocoons from a trusted local mason beekeeper like Brian who checks to make sure he sells disease-free Western mason bees.


  1. Hi, Nice article. I think that the mites eat the egg and small larvae but not adults inside a cocoon.They cannot open the cocoon. I use a Dinolite with my Mac. A little expensive but well worth it. Have a look at my web site Cheers, George

    1. Thanks for clarifying that George. I will check out your site!