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.

Osmia species

Cocoon sizes 012010 004Frank M.  writes:  I’m sending this image to you to get an opinion about something that continues to puzzle me. These cocoons are part of my current crop. It’s perfectly clear that the three stacked on the left are females, and the three stacked in the middle are males, but are the three tiny ones stacked at the right end also Mason Bees? I’m finding quite a few of these tiny ones and although they look like Mason bee cocoons, the small size makes me wonder if I’m getting a sub-population of something else.

I will be grateful for your comments. In addition to your views about the very tiny ones, how about the two between the left stack and the middle stack? The one on the left is almost certainly a female, but what about the second one?

Dr Margriet replies:  These all look like Osmia lignaria  I assume that all these cocoons came from nesting tunnels with a diameter of about 7.5mm/ 5/16″.  If so, these are highly likely Osmia lignaria.  There are many smaller species of mason bees  but these are more likely to be found in nests with a diameter of 3-5mm.  The difficulty is with identifying according to size is that cocoon size is on a continuum from small to large
The females range from small to large and the males range from small to large. I am sure the very small   ones are males and the very large are females. The ones in the center are the real question. The only way you can really find out is to see them after emergence. 

I found this bee last spring and realized today that she has no wing on one side and what appears to be a deformed one on the other side. So far I haven’t seen others with this problem, but it’s still early.   She crawled under a folding chair and was protected. Have you heard or seen anything like this before?

NoWingBee NoWingBee2Great photos Valer.  I have seen wingless honey bees, but never wingless mason bees.  In honey bees the cause is a Deformed wing virus.  This virus or similar virus could be the cause of what you observed.   Dr Margriet


Summer bee cocoons covered with red frass


Red frass scraped from some of the bee cocoons

Here are 2 pictures of summer mason bee cocoons  (? species)  with  small red fecal pellets on the outside of the cocoons.  What is interesting each of the cocoons has the bright orange pollen fecal pellets or frass.  it would be interesting to know the flower that provided the bee with the orange pollen and then know when this bee was out and about.  Helen mistook the frass for large mites.  She dusted them off, but this could cause more damage to the fragile nature of this type of cocoon.  Dr Margriet

don z osmia cornifrons2 Don reports having both brown cornifrons and black osmia bees living side by side for years.   Great photos Don.  Thanks for sharing

Hi,   I have a number of bees at one of my houses this year. I’m familiar with the Blue one but wondering what the reddish –Brown one is? Would appreciate any assistance identifying. Thanks  Norm.

Looks like the reddish one is Osmia cornifrons.



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March 2017
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