Bombus melanopygus bumble bees using Mason Bees nesting tunnels

From MB

I’ve been keeping mason bees for four years now and earlier this month I came across something I have never seen/read/heard about before.

One afternoon I noticed a big bumblebee — a big bugger, about twice the size of a mason bee with a tiger-striped orange abdomen — hanging around my mason bee houses and fussing about at the end of one of the tubes. I later observed the same bumbler entering already occupied tubes on more than one occasion. I figured the bumbler was simply stealing the pollen already gathered by the mason bees — you know: working smarter, not harder.
Then one evening I was checking the mason bee house with a flashlight and noticed that in four of the tubes, there was a thick, viscous liquid inside. The taste test doesn’t lie — it was honey.
I emailed Margriet and asked some of the questions running through my mind: Is this common? Do bumblebees hijack mason bee tubes for themselves?
I already have 20 tubes filled up so I have more than enough mason bees for next year. I’m no interest in killing the bumbler but its behaviour was fascinating.
Since then I did some research and, combined with my observations, I have concluded the bumbler in question is an orange rump bumblebee queen (Bombus melanopygus) who has apparently made an odd choice for a nesting site (image: Queen). She had taken possession of a row of four mason bee tubes, each of which contains globs of honey. If you look inside the tubes in image: honey, the little gleams of light are actually the blobs of honey. (I have a better shot of the honey but I can’t get my email to work on my iphone right now).
She goes in and out of the tubes but has to back out of them because she is too big to turn around inside like a mason bee can.
One evening when I returned home from work I was lucky enough to watch as the queen used her wings to fan the entrance to one of the tubes (image: bumbler1A). I’ve read about honeybees doing this at the entrance to a hive so it was interesting to see. When she was finished, I was able to get the second shot (image: bumbler 2).
There are also now a couple of worker orange rumped bumblebees on site and one of them has taken possession of another tube. They are much smaller — but still bigger than a mason bee — with just a dab of orange on the end of their butts.
I have two mason bee houses located side by side but the bumblers show no interest at all in the other house. The bumblers are now very active as you can see by the heavily stained appearance around the end of their tubes (image: tubes). I believe this is caused by dirt and pollen tracked through the honey by the busy bumblebees. They are still producing honey.
From all appearances, the bumblebees have set up shop in the empty mason bee tubes for the remainder of the summer. I have 10 empty ones left so there still room for expansion.
Thanks Michael B.  for some great photos and some neat observations.-Margriet
Bumbler IA

Bumbler 2


Honey on base of tubes

3 replies on “Bombus melanopygus bumble bees using Mason Bees nesting tunnels

  • DAB

    That is fascinating, since Bumblebees normally nest in or close to the ground. Would love to know more about the placement of your bee house.
    I assume you originally witnessed this behavior in early spring, when females begin nesting?
    Thanks for sharing!

  • Glen Buschmann

    This is indeed fascinating.

    Two things about B. melanopygus.
    They, of all the bbees in the PNW, are the most likely to use an above-ground nest box, including abandoned filled birdhouses.
    They are also the earliest of all the bbees around here, overwintering queens emerging to forage even on warm January and February days. By now these bbees are almost finished with their nesting cycle; their cycle seems closely tied to rhododendron flowering.

    This doesn’t explain for me the honey storage; there must be something odd going on in the nest — too many workers? Where is the nest?


    • Margriet

      Honey storage by bumble bees is done to tied them over periods of bad weather. Once they all leave the nest , there may be honey pots with some honey left in the abandoned nest. Let me know if my answer does not answer your question. Margriet


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