My name is Dr Margriet Dogterom and am the founder and owner of Beediverse. I write this blog for all who love bees and who want to learn more about these wonderful creatures.


Kristy writes:  Our first spring with mason bees about half our bees hatched. Of those bees they filled about 1/3 of one of the houses. But the next spring they were eaten by something and nothing hatched.  With some  additional mason bees  a few slots were filled, but something got into the nest and nests are now empty.  em from being eaten. After cleaning we went from 5 filled slots to what looks like 4 cocoons that are healthy.  The rest have worms, earwigs or flys in them.

REPLY:  It looks like you have a few cocoons for next year. Set these out in the spring. It sometimes takes 2-3 years to build up a population that uses the nesting holes.  First they use all kinds of natural nesting sites.  Yes, protecting bees from predators is a big item.  It looks like some of the cocoons are moldy.  But this mold does not harm the bee inside.  Mold is easily removed when washing cocoons.  Do harvest them as early as mid September.  While they are stored, they are potential food items for all kinds of predators.  Do  you have a copy of my book Pollination with Mason Bees? Perhaps reading through it you will come across other ideas you may not have thought of.   If you can attend a workshop, this would also be helpful.  Dr Margriet


FROM LESLIE:  I’ve followed the steps to clean the cocoons as outlined in your book. The cocoons were really heavily covered in mites, and there were many parasitic wasps present on and within several cocoons, which had holes in them (and which I discarded).
My question is how to clean the remaining mites off cocoons.  The remaining cocoons are still not as clean looking and shiny as the ones I typically buy from Wild Birds in the spring. There’s some webby material still present on the outside, and what looks like possible clumps of mites.  Should I rewash the cocoons and put them in the bleach solution again?

pollen mite X

a microscopic look at the pollen feeding mite.

floating cocoons-mites_edited-1

A mason bee cocoon covered in mites


Wash cocoons in a large bowel, under running water and inside a sieve.


For about 30secs to a minute, scour mites off cocoons by rolling cocoons in a metal sieve and under running water

REPLY: Yes, do wash them again under running cold tap water.  Use a metal sieve that will scour mites off the outside of the cocoons. use a bleach as the final wash to make sure that there are no fungi on the cocoons.   Dr Margriet


Candling. If lots of light shines through the cocoon, there is no mason bee inside the cocoon.

Wasp cocoon

Four adult parasitic wasps inside this cocoon. Search and destroy, or wasps will destroy your bees.

This candling video shows the technique of candling.  Set up a 6V flashlight in a dark room.  Place washed and cleaned cocoons in a petri dish.  Rotate petri dish over light to more clearly see what is inside cocoons.  Remove parasitized cocoons.  Go to shop beediverse on this web site to order petri dishes.



Adult bees while hibernating through the winter in their cocoons, are curled up leaving a small area through which light can pass. These cocoons appear mostly black with a bit of light passing through the center of the cocoon.


A cylindrical area in the centre of the cocoon is often an underdeveloped bee that died during development.


Wasp cocoon  Well not exactly.  We are candling mason bee cocoons here.  Placed in a petri dish and on top of a flash light, parasitized cocoons become translucent showing  the parasitic wasps inside.  This cocoon shows at least 4 parasitic wasps.  The thing to do?  Destroy!  More about candling tomorrow. Click on this link to purchase a petridish  from Beediverse


“Back when I was cleaning up my cocoons I found three with a tiny hole in them. The hole was about the diameter of a straight pin shaft. Inside each I found 10 to 15 tiny winged insects metallic green in color. All of them were dead. They are about .03 to .04 inches long. Attached (I hope) is a microscope photo of one of them. Also attached is a photo of a cocoon with a cluster of the little guys. Do you have any idea what they are or why they were dead?”Hal

These are  tiny parasitic wasps that grow inside a bee cocoon.  Looks like there are more than 30 out of one cocoon.  Good thing you found it.  Candling cocoons can also identify them.  These critters can wipe out a mason bee colony.  Wasp proof nests are a great way of protecting your bees from parasitism.  If was probably too cold when they reached maturity.  The last batch of the season did not make it.  Dr Margriet 


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