• When do Leafcutter bees emerge?

    Leafcutter bees are great summer pollinators.    It is easy to start with these bees.  All that is required are bee cocoons, a suitable nest and some hot summer weather.

    Many of our customers have started their new hobby with these great little summer pollinators.  But it was not clear how long these bees needed to develop into adults and emerge in the summer.  We heard of people throwing them out, cutting them open and finding  a fleshy grub that does not look at all like a bee!

    Here are the facts.  Under laboratory conditions and inside an incubator at 30C, bee pupae need 20-31 days to emerge as adults!

    This is a long time!  This means that under normal conditions (and about half the time it is night and temperatures are cooler)  the emergence time is much longer than 21-30 days.  Under any natural conditions, emergence is more like 30-45d+.  They say ‘Patience is a virtue’!


    Twenty two species occur in Western Canada.  Megachile rotundata is a species of leafcutter bee that originates from Eurasia.  It is used in the commercial seed production of alfalfa.  The female Megachile rotundate has silvery gray hairs on the underside of its abdomen.  Other female leafcutter bee species usually have golden, tan, or black hairs on the underside of their abdomen.

    Megachikle rotundata overwinters in the pre-pupa stage. during last spring and early summer, temperatures are sufficiently warm for pre-pupae to develop into adults.  Then adults emerge to pollinate our summer blooms.

    Nesting material for leafcutter bees were first made out of grooved wooden pine boards that were stacked to make a series of nests.  Polystyrene grooved boards and nesting holes molded into solid polystyrene blocks are both used today.

    In part, excerpted from our book ‘Pollination with Mason bees” page 100 by Dr. Margriet Dogterom.  Get yourself a copy as 25,000 others have done.  It is the standard management guide for mason bees and includes details about other bee species.



  • Success With Overwintering Cocoons using a cooler-Beediverse

    With every technique and system there is a good way to do it and there is a not so good way to do it.  It is the same for various techniques used to safely overwinter bee cocoons.  There are 3 main things to keep in mind when storing mason bees:

    • Keeping predators from eating bee cocoons
    • Preventing bee cocoons from drying out
    • Preventing bees from coming out earlier  and or in the wrong place (like a storage shed)

    The easiest way to keep rodents away from eating the cocoons  is to store them inside a fridge.   To keep cocoons from dehydration inside a fridge place cocoons into a Humidity cooler.  But do check for water inside the Humidity Cooler.  An alternative is to store them outside.  If outside storage is preferred, keep cocoons in a cookie tin with a few air holes in the lid.

    Adding water onto a pad to keep cocoons moist.


    The metal tin will prevent predation.  Outside storage only works however until temperatures warm up.  The cocoons will have to be moved to the mason bee home for release as Spring arrives.  Releasing them from a Castle or other home will make sure the bees emerge at the right time at the right location.

    A small fridge with manual defrost is the best fridge for storing mason bee cocoons.

  • What is this Cotton fluff?

    Tony W. writes  “I found insect pupae embedded by fluff this winter. There was also a stash of plant pollen also wrapped in plant fluff. A cavity in a timed water valve was completely filled by these items. I see that there have been comments on your blog mentioning these. I have come up with an answer as to what these are. I believe they are wool carder bee pupae. I damaged some of them trying to figure out what they were but have four left with one in quite good condition. With luck an adult will emerge and I can reach a firm conclusion. However, the descriptions of overwintering by these bees fits what I found quite well. ”  see link   http://www.nativebeeconservancy.org/native-bees/wool-carder-bees/               There are several articles and posts about this bee.  This picture is from another blog post.  To see other articles about this bees use the search window in the upper left corner of this blog and use the word-   cotton   You will find  additional articles with pictures .  Dr Margriet




  • Leafcutter bee emergence-a full report and more!

    Hi Margriet,

    The first thing I want to mention is that I did compare your Canadian leafcutter bees to some leafcutter bees purchased in the United States. I incubated both sets of bees under the same indoor conditions where the leafcutter cocoons were placed in plastic petri dishes with a plastic lid that holes drilled in it for air circulation. I also had an internal temperature probe in each dish to monitor the temperature, and both temperature and humidity were recorded on a daily basis to an Excel spreadsheet. I also took notes and put them on the spreadsheet as I examined a few cocoons over the incubation period.


    My results on leafcutter bee “emergence” rate would support what has already been published in the literature (see PDF). That is, under my incubation conditions I found that the Canadian bees were much better than the U.S. leafcutter bees in the percentage of bees to emerge. That is, I had 99% of the Canadian leafcutter bees as compared to only 55% of the U.S. leafcutter bees emerged over the same time period.

    The other thing that I found, which I would do different next time, is that the required temperature of 86oF (30C) for the bees to emerge by 28 days is probably very critical. When I received both your bees and the U.S. bees at the end of May, I decided to try and incubate them inside my house where the temperature is more constant. During May and June in the Portland area we still have wild swings in temperature where it can be 64oF (17.7C) for many days or weeks in May and June.

    With the indoor incubation I was only able to maintain an average daily temperature of 76F (24.4C) as compared to the needed 86oF (30C), which resulted in the bees only beginning to emerge (the males) at 30-32 days instead of the standard 18-20 days. Fortunately when the first males began to emerge I put them all outside and our daily temperatures were then in the 80-85F (26-29C) range. Again, despite the longer incubation time I still had nearly all the Canadian bees emerge as compared to only about half of the U.S. bees emerge over this same time period.


    The retention of the leafcutter bees was a surprise to me in that only 5% of the Canadian and none of the U.S. leafcutter bees decided to take up residence in my nesting box area.

    Where I put the bees for release was actually within the middle portion of my Mason bee nesting structure (that faces East), and it contained many empty round tubes with and without papers liners, two of your corn stacked-systems, and many of the natural reeds at various sizes.

    Also, on the other side of my nesting box are rose bushes, a big lilac tree, azaleas, a redbud tree, and many other plants that leafcutter bees are supposed to like for nesting material. We also have a very large Wisteria plant that actually hangs near my mason bee nesting area, and I could find many of the leafcutter bees on the Wisteria flowers as well as on other flowers all around my house. However, despite being in close proximity to my nesting box on the flowers that very few bees decided to take up residence. Wherever the bees decided to go I hope they survive the winter and come back next spring.

    I am curious though what you or others have done to have good retention of leafcutter bees?

    Anyway, it was very fun to have them as summer bees, and I definitely would order more leafcutter bees from you next spring and try a few different things. I have also taken a lot of video of the leafcutter bees on our flowers, and when I have time I plan to process the video to extract some still photos to send to you.

    Best regards,

    Michael, WL Oregon

    Thank you Michael for sharing your findings.  The Abstract from the scientific article is given below.  Dr. Margriet

    Emergence success and sex ratio of commercial alfalfa leafcutting Bees from the United States and Canada

    J. Econ. Entomol. 98(6): 1785Ð1790 (2005)
    ABSTRACT Samples of overwintering alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera:  Megachilidae), cells were sent to the laboratory as loose cells or in nesting boards from bee
    managers in the United States and in Canada. X-radiographs of cells were used for determining cell
    contents. Cells containing live prepupae were incubated, and the sex of emerging adults was recorded
    daily. Cells from which no adult emerged were dissected to determine the developmental stage of dead
    bees and sex of dead pupae or adults. Bee cells incubated in commercial settings and placed in alfalfa
    fields by the same bee managers described above also were evaluated to determine adult emergence
    success. The proportion of live bees in wood nesting boards from the United States was much lower
    than the live proportion in polystyrene nesting boards from Canada and loose cells overwintered in
    the United States. For laboratory-incubated loose cells, survival and sex ratios of bees from Canadian
    sources were statistically higher than those of U.S. bees, but the onset and duration of emergence times
    were similar. Fewer bees survived in the commercial setting than in the laboratory. Prepupal mortality
    was signicantly higher than pupal or adult mortality, but there was no significant difference between
    the sexes in the likelihood of survival during incubation. This study supports the commonly held belief
    that alfalfa leafcutting bees raised in Canada and then sold to the United States represent a more viable
    source of bees than most bees produced in the United States.

    KEYWORDS: Apiformes, Apoidea, Megachilidae, Medicago, lucerne

  • What Mason bees are these?

    Hi,  I put out a box of 7mm tubes next to my normal 8mm  tubes for the Orchard Mason Bees or Osmia lignaria. The  mason bees are doing very well filling their tubes. Attached is a picture of the 7mm tubes, they have 5-7 bees working in them. Most are horned Face (Osmia cornifrons) but a couple look like the regular Osmia lignaria but are much smaller as can be seen in the picture. My question is are they just small Osmia lignaria that prefer the smaller tubes or is there another species that I don’t know about? From what I can tell they look like the Osmia lignaria but are about the size of a Horned Faced. Thanks                  Norm

     Hello Norm, Thank you for this fine photograph.  I see two bees quite clearly, and the third is a bit too blurry to see what it is.    I do not have any experience with the horned Face mason bee, but it has brownish coloration as the lower bee (see link below).  The black one is  Osmia lignaria.   Both are early spring pollinators, and so both would be about  in early spring.  The size of female mason bees or Osmia lignaria varies quite a bit.  I do not know if this is genetic variation or the end result of varying levels of nutrition.  It is unlikely that there is a third species of a smaller size in early spring.  However, many more smaller black mason bees are around that come out late spring through to  late fall.  at what time of year was this picture taken?    Dr Margriet Dogterom







  • 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

  • Osmia californica bees and nests

    Michael emailed me with a question on setting out new nests when the old nests are getting filled.  He asked if adding a nest close to the others would disorientate the bees already nesting at the location.  
    I suggested that additional nests are best set out in the visual range and clustered close to the original nests. 
    Michael also noted that his bees headed for the tubes first.  Yes mason bees prefer round holes, especially when the substrate is wood or carboard.  Unfortunately the bees’ choice is not always the best for eaze of management. 
    Michael’s original question was:
    If I need to set out more nesting sites for the Mason bees should I put them next to existing sites, or, put them a bit away from the one’s I originally set out?  The reason I ask is that I am getting many more bees to nest so far this spring compared to last year but I do not want to mess up the bees visual cues to the old sites.  I also know they like to be near each other.  Your thoughts?
    Michael’s follow up notes are:
    As I mentioned before I was particularly surprised by what happened this spring when most of the O. lignaria emerged at once with a very low dispersal rate.  This activity was in contrast to the last two springs where the dispersal rate was high and emergence rates were very sporadic.
    In my nesting set-ups, which I have two of them around my house (see the BEFORE photo), I put 40 cocoons in the wooden house, and 20 cocoons in each of the tube units (80 total of O. lignaria).  There was also 20 of your O. californica cocoons in the wooden nursery house.
    I set out all of my bees on April 20 and to my astonishment, almost all of O. lignaria had emerged by April 22, and the first mud nests were made in the tubes on April 24.
    The second surprise was that all of the bees decided to move to the tube units (reeds and paper filled tubes).  This is where I was beginning to get concerned that I would not have enough nesting sites.  We had a week of very good weather, and then we had four-five days of cool and damp weather which I then decided to put another tube unit below the existing two tube units (see AFTER photo).
    During this cool period of weather, I noticed that all the O. lignaria bees were resting in the tubes, so I kept track of what bees were in what tubes and how far they had gotten along in building their mud nests.  The good news is that when the good weather returned last weekend that all of the existing bees resumed their normal activity and were not deterred by the NEW unit below!  It seems that putting a new nesting house nearby did not distort their visual cues (at least under my conditions).
    Also, in taking the pictures of my nesting sites last weekend I noticed the O. californica I purchased from you were beginning to emerge.
    I just managed to snap a photo of a O. californica male and female bee doing what a pair of bees are supposed to do .
    It might also be my imagination but it appears that the O. californica seem a bit larger than the O. lignaria, and so far all the O. californica bees are headed for the tubes.
    Maybe it is some kind of social communication or interaction, but who knows what the bees are really thinking!
    Best wishes,
    Mating Osmia californica


  • Osmia californica

    Osmia californica comes out late in spring, often their emergence overlaps the latter end of the Osmia lignaria (early spring mason bee) season.

    However very little is known about them.  If you’d like to share your photos of Osmia californica, please email them to me and I will get them on this blog.

  • from Holland- Osmia rufa

    Roeland Segers from Holland contacted me the other day about nesting alternatives.  We continued our conversation about Osmia rufa, an European Mason bee.  I asked if he would like to share some of his photos with the blog and its readers.  I was most delighted to receive the following photos.  If you’d like to contact him direct, go to his web site.  The website is in Dutch with some gorgeous photos.  He writes
    ”  My company has recently been rebranded to: De Bijen, Bestuivingstechniek (translating to: The Bees, Pollination techniques) from Nijmegen in the Netherlands. My websites: for masonbees http://www.metselbijen.nl/ (for honeybees http://www.rendementdoorbijen.nl/ )”

    Roeland’s mason bee web site

    Mason bee se-up while pollinating cherries.
    Mason bee nests are made of routered channels cut out of compost board.
    Boards are held together with a tie-strap.  


    Osmia rufa doing the finishing touches to her nest.


    Osmia rufa male.  Note the long antennae.


    Females resting over night inside their nesting tunnels.
    Embrace (Osmia rufa)
    Fierce competition
  • Discovery of new Sweat Bee Species

    Researcher discovers 11 new sweat bee species, four in New York City area
    Alfonso emailed me today and let me know about this interesting research.  He adds-
    “I bet if we really surveyed what we had, we could come up with some incredible results of what’s really out there. Alfonso”

    Click here for the full story