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.

Inside the Mason Bee Nest

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Black/ brown oblong rods are fecal matter from mason bees

I’m hoping you can help me identify some pests that infested my Mason bee stacks.
I cracked open my corn resin stacks today to clean and store my cocoons for the winter and was surprised to find two different insects  ? parasites.  Are you able to tell me what these items are? And the little black mite-looking things?

REPLY:  The brown oblong items are fecal material from cocoons.  It does look like something (perhaps a beetle scavenger) has entered the nest and has eaten all the mason bee cocoons leaving the fecal pellets.

The white grubs I believe are fruit fly pupae.  Fruit flies lay the eggs on top of the bee pollen lump.  The fruit fly larvae consume the pollen leaving nothing for the bee larvae.  Dr. Margriet

Hi Margriet: “Further to our brief chat a couple of minutes ago I attach a couple of photos I took of a nesting box today. You will notice the stringy brown material (fecal matter??) and the yellowish coloured larvae (or pupae?). I have never noticed this brown material before but the yellow guys seem to be present in large numbers this year.

Would appreciate any comments you can provide on this situation.  Many thanks.  Mike N., North Vancouver BC


“Hi Mikemason1,  Great photos.  Yes the curly material is fecal material.  The yellow ‘grubs are pupae.  The culprit is the spider beetle Ptinus californicus.  The female beetle lays 4-5 eggs and these consume the majority of pollen provisions meant for the developing bee.  They may also eat other developing bees which they either injure or kill.  They are an opportunistic scavengers.

and a quote from my book “Pollination with Mason bees”  on page 90 “Removing these beetles from the nest when nests are cleaned is a good opportunity to keep the spider beetle population low so it does not become a serious pest.

wasps from mason bee houses 002 wasps from mason bee houses 001 Rachel emailed me these photos.  Would you be able to identify this particular wasp species? I think it isn’t a parasite but rather just another opportunist who needed a hole to live in. I had so many parasites this year! I have pics of several and have identified most. Another thing I found interesting thing I found were several flies (much like green bot flies) that were also living in the tubes. What a fascinating world I’ve come across. Any help identifying any of these would be appreciated. Thanks.



Here is the wasp that makes the cylindrical cocoon.  Anyone know what species?  Dr Margriet



Cocoons in Block 2

Lower row: cocoons in question. Mid row: mason bee cocoons. Upper row: leafcutter bees.

I have attached pictures of cocoons in block also a large wasp that used dried grass to fill holes.  Thank you for the quick response, Ken


Does anyone know what insect makes this cocoon? Dr. Margriet


Wasp Unknown Cocoon 5 Unknown Cocoon 2 Cocoons in Block 3

“Hi Margriet .. I’m a little late in sending you my usual “annual report” on the cocoon harvesting by my group this year, but it’s in progress.  I will have some interesting images and questions.  But in the meantime, I want you to see this example of some very aggressive nesting that turned up during the processing.

Here’s the story, and it’s a modified version of what I sent out to the 20 members of my sharegroup.

One of my guys took 35 of his cocoons to Duncan for his brother-in-law to set out. Which he did.  He  had a stack of five trays with eight galleries per tray.  That’s 40 galleries.  The yield from these trays was 330 cocoons!!  That gives a multiplier very close to 10 .. which is possible, ’cause I had results like this back in the late 90’s.  But in this case I’m told that there were already lots of bees flying around his brother-in-law’s garden, so he undoubtedly captured many members of the natural colony .. just like I’m doing at Ten Mile Point.

 What’s particularly interesting about this case is how aggressively the bees nested.  Image A is a side view of the five trays.  Note that the lowermost two trays don’t reach all the way to the back of the stack, leaving a gap behind them.  Note that there is also a gap between the lowermost tray and the one above it because the trays don’t stack properly.

Image B shows what the bees did in the gap behind the lowermost two trays. They built a sheet of chambers on the wall behind the two trays.

Image B


 More surprising, Image C shows the top of the lowermost tray.  Not only are many of the galleries filled, but there is a sheet of chambers on top of the tray, filling the gap that existed between it and the tray above.

Image C


 SO, the moral of the story seems to be … when the bees are determined to nest and conditions are right, nothing much can stop them.  And I suppose the corollary is that when the bees are NOT interested in nesting, it’s difficult to persuade them to do so.

I now have three examples of nesting boxes interacting with natural colonies.  This one, where the bees from the set-out cocoons  plus bees from the natural colony were happy to populate the nesting box together. 

The opposite situation is the nesting box and cocoons that have been set out for three years at one of our Victoria sites where there is also a natural colony, and every year so far the bees have emerged and joined the natural colony, with absolutely no interest in the nesting box. 

And the third example is a site I have in Victoria (the Ten Mile Point site referred to above)with a very large natural colony in a large garden, and where I set out nesting boxes each year and harvest lots of cocoons.

I’ll have a report on our cocoon harvesting to you soon, and by the way, please feel free to use any of these images and the ones coming with the report – with an acknowledgement of course.

Best wishes for all good things in 2014.


Thanks Frank  awesome pictures and a great story.  Dr Margriet Dogterom




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