mason bees wild bees and native bees

A sign that it’s time to free your mason bee cocoons

A healthy male mason bee sipping nectar from Vinca minor. Photo © Rusty Burlew

Mason bees tubes and cocoons should be outside when the first flowers bloom in spring.

Inside: Mason bee cocoons need a few days of warmth before the bees emerge. In nature, the bees emerge when the first flowers bloom in spring. You can wait a while longer if you have a specific crop to pollinate, but waiting too long is risky.

If you are keeping mason bees in cold storage—whether in a garage, shed, or refrigerator—when is the best time to put them outside? Although conditions differ with latitude, nature tells us when the time is right.

As a rule of thumb, as soon as things begin to bloom, the mason bees should be free to emerge. The blooming plants you see should be within a couple of hundred feet of the mason bee housing. Unlike honey bees, mason bees will not fly long distances to find food, so it has to be close.

Early blooming plants here include crocus, scilla, vinca, skunk cabbage, and snowdrops. Forsythia, dandelion, and Indian plum (Oemleria cerasiformis) come next. Once you see a few things start to bloom, you can safely put your bees outside.

If you don’t trust yourself to remember by looking at plants, just think March 1. Spring mason bees (Osmia lignaria) are generally active in March, April, and May, so March 1 is a reliable date to use.

You can wait for certain crops

Some people like to regulate the timing of mason bee emergence so it coincides with a particular crop they want to pollinate. This works to some extent, but be careful. It can take a couple of weeks for the bees to emerge once you remove them from cold storage. If you wait too long to put bee cocoons outside, your bees may emerge too late.

Although some folks will keep mason bees in cold storage through April, I think it is better for the bees to be active when their wild counterparts are active. This will give your bees the best opportunity to mate with local wild populations and maximize genetic diversity.

Keep your mason bees safe

You can minimize the danger of wind and cold with a few simple steps:

  • Attach a sloping and overhanging roof to your bee house to shed excess rain, or mount the bee house under an eave.

  • Plant early blooming flowers close to the mason bee housing. The males will emerge first and need nectar-producing flowers right away. The females will emerge later, and they will require both nectar- and pollen-producing blooms.

I saw my first mason bee last week on March 13. He was drinking nectar from a Vinca minor while all around him honey bee workers and queen bumbles were working the Scilla.

Rusty Burlew
Honey Bee Suite


  • Ooh, you’re making me feel like I’m behind on my duties! I always wait for the Spring Equinox, and even then I only put out a portion of my cocoons, maybe 25%. A week later, I put out another 25%. I put out the rest when I see mason bees have hatched and are using my nest.

    Colorado winters have a bad habit of not wanting to end. Last year each time I put cocoons out, we had an unexpected snow storm. Each time, it was cold enough to destroy whatever was flowering… no maple blossoms, no crabapples, no ornamental pears… poor bees had nothing to eat. I finished the season with fewer cocoons than I started, and the cocoons I have are on the small side. 🙁

    I worry that my bees are using up their fat reserves, but I am still waiting for the buds on my pear tree to swell just a little bit more.

    • HB,

      If you’ve got a system that works, you shouldn’t feel bad. All beekeeping is local, even mason bee keeping.

      • Hi, I live near Mt Hood and it’s my first year of mason beekeeping. I kept them in their tubes in an old refrigerator. It’s April 1 but looks like the weather could be just at freezing one day this week. Should I take out a few and stagger putting them out when there’s more bloom? Nothing is blooming in the orchard yet but plenty of wildflowers in the surrounding forest!

        • Patty,

          I like to put them out toward the end of March. Remember, it takes them a couple of weeks to register the warmth and start to emerge, and you don’t want to miss the early fruit trees. You can wait a while longer, but you could possibly miss your target crops.

  • Hi Rusty, Just new to your site but it looks so informative! Do you have a favorite type of house for your mason bees? If so, can you tell me your preference? One with removable straws or not?
    Thank you,

    • Barbara,

      If you want to raise just mason bees (rather than housing a variety of bee species) then I would use paper straws. Hairy-footed mites are definitely a problem when you have a monoculture of mason bees.

  • HI Rusty –

    Unless the beekeeper is running a commercial operation that must manipulate emergence, I encourage people to put stored mason bees out early and let nature set some of the schedule. Males emerge first, assess conditions, and if warranted helps females get out, (he cuts open the cocoon from the outside, pulls her out of her sleeping bag). Tunnel systems, (this includes straws) seem better than loose cocoons for this, as the cocoons are in order – males in front, females in back. Bees generally stagger their emergence based on conditions, waiting for breaks in the weather.

    Of course Colorado is different than PNW, and bees are kept in the fridge as much to protect them from getting too cold as too warm. I wonder if there may be other native pollinators better suited to conditions described, (they maybe won’t live in human-made housing, but that is o.k. The challenge is that the natives may be unaccustomed to some of the early blooming Eurasian crop plants we grow that bloom on a schedule different than Colorado. I also might also look into outdoor storage that is better insulated against temperature fluctuations. As you point out Rusty, the closer to the local ecosystem the better.

    Bees seem to vary their size quite a bit, depending on both food and housing available. I had a male mason bee emerge today bigger than the typical female, from one of my larger diameter tubes. But small works, might be better in some circumstances. Maybe Colorado mason bees will prosper better as small bees in 1/4″ tunnels.

    My favorite system is botanical tubes — empty hollow plant stems. One reason I like botanical tubes is size variety. Botanicals also can go outside with less protection. Because every location is different I won’t name specific plants except to mention that some folk use bamboo which works but is tough to cut. Instead, I’d explore, cut different tall fast-growing plants and look for hollow stems. If suitable, then give the stems a try. Paper straws work fine, but paper is water absorbent, so they need more external protection. I make my own by rolling newspaper around a 5/16″ or 3/8″ dowel. YOU MUST LINE EACH NEWSPAPER TUNNEL WITH PLAIN PAPER, (no newpaper ink exposed inside the tunnels).

    Glen B
    Olympia, WA

  • Hi Folks – new to this site – caught you via a Google Alert. re: this topic – I am confused. By the question I assume you are bringing your mason bees inside somewhere and then putting the back out again? From my experience, I question why this is/was done. Mason bees that build out into an artificial or natural space will emerge when they are programmed to – “need to” – if you will. I can see no reason to bring them in unless there is a fear of predation by some other insect or animal. In which case, I would still leave them outside and take measures like hardware cloth or a high location to take care of this worry.

    Steven Lechner
    Busy Bee Farm
    Larkspur, Coloraodo

    • Hi Steven,

      Welcome to the site. Yes, I agree. I do not bring my mason bees inside, but there are people who do. One of the reasons here in the Pacific Northwest is the rain. Here in the coastal areas we have rain from October thru June—basically nine months of it. I go out of my way to keep my mason bees sheltered, but if you don’t have shelter they will “sog out” by spring—mold, fungus, you name it.

      The other reason people may have them indoors is because they mail-ordered them. They arrive in a loose tube, not a good overwintering site, so people keep them inside till spring. I wrote the post for those people who have mail-ordered them and are unsure when to put them out.

      I agree that outside is where they should be so they can overwinter properly and decide for themselves when to emerge. Not everyone agrees with that philosophy, however, and so I’ve tried to give those folks some guidelines for choosing a time.

    • Steven, I live in Colorado just west of Denver. Do you think I can have success in raising mason bees? I have a lot of fruit trees, but they don’t bloom till around the middle of May. Thanks Ron

  • This is my second year with mason bees. As I understand it one major reason to bring them indoors for winter is to keep them away in the fall from parasites. I noticed some parasitism on some cocoons left outside past June 1st. I would rather keep them outside all year but had parasites the first year so I’ll continue bringing them in.

  • I refrigerate my cocoons because of the erratic temperatures. A few days above 50 in February, and the bees might start emerging and find no blooming plants to feed on.

  • This is new territory for me overall. I am merely exploring the idea of a bee house, but have one big question. IF they collect and store their pollen and turn out to NOT be mason bees that seal the openings, will this be in conflict with the 3 hives of honeybees already on the property? Will this encourage robbing from them?

    • Melissa,

      I don’t know if I understand your question. The only thing that will build in the tubes are solitary bees (there are many species besides masons that could build in the tubes, depending on the hole size) and a few types of solitary wasps. None of these insects pose any threat to a honey bee colony. Robbing of honey bee colonies is conducted mainly by other honey bees or by social wasps that also live in large colonies, such as yellowjackets and some hornets. Also some ants attack honey bee colonies, but again, ants are social and live in large colonies.

      There is no colony behavior with solitary bees and solitary wasps, which is why they are called solitary. One female bee or wasp builds and maintains her own nest. They may live in communities, but each nest (tube) is maintained by one female bee. I can’t imagine anything living in a mason bee house being a threat to a honey bee colony.

  • Hi from Colorado Springs, CO. We were watching PBS and saw a show on Mason bees. Now we are interested in building our own house to put in our 8×10 ft garden. Being late March, we will put it out now. Glad to find a site where we can ask questions as we continue in this process. Thank you.

  • My mason bees started to emerge and there’s no flowering going on, some dandelions, none of my fruit trees yet, they’re about two weeks from bloom. It’s April 28th and were still getting snow. Will the bees that have hatched make it, and is there a way to put off the hatching in the future till the second week of May?

    • Ron,

      There’s nearly always something in bloom, and the bees are better at finding those things than we are. Mason bees are fine in cooler temperatures than many bees, and they know how to care for themselves. You can put off hatching by keeping them in the refrigerator, but you don’t want to go too late. The males hatch a week or so earlier than the females, and you don’t want your fruit trees to come into bloom with only the males around.

  • I recently bought a mason bee house if I hang it near my garden will the bees move into it? or do I have to buy bees? Should I wait until spring to set the house out or should I put it out now?

    • Cathy,

      You can just put the house outside, and if you position it well, local mason and leafcutting bees will nest in it. It is my belief that it is better not to buy bees because locally adapted bees will do better, and you don’t run the risk of introducing a bee pathogen or parasite. The openings should fast south or southeast and be in the sun most of the day, particularly in the morning hours. I don’t know where you live, but I like to put them out in early spring before the first fruit trees bloom. If you put them out now, you run the risk of getting earwigs and other undesirables. I put mine under the eaves of my house and garden shed, which adds a little rain protection. It’s fun to watch the bees build. The mason bee species will seal up their holes with mud, and the leafcutting bees will use colorful petals or leaves. Too cool.

  • Hi,

    I live in Monument, Colorado and I put out my mason bees attached to a tree and a few days ago they were moving around and coming out of their box… We had a snow storm last night and I went to look at them this morning and they all looked dead. The temp got in to the mid 20’s…

    Do I have to worry?


      • Thanks for the reply.

        One other thing. I put my mason bee house in a south facing tree with the “box o bees” I just purchased with a hole in the bottom attached to the tree right above them. Is there anything I can do to prevent the birds that may fly by to not to eat them?

        I put up old silver CD’s hanging to deter them.

        thanks again

        • Kevin,

          I don’t think so. Some people put chicken wire or something similar around the nest to keep birds from pecking into the holes, but birds can get the bees while they are out foraging too. It’s one reason bees lay so many eggs—to assure some make it.

  • hi…

    Another question. I got a box o bees and when they arrived a few were in cocoons and a few were alive and moving around. I purchased a Mason bee house. I was wondering if I should insert the cocoons in the hive and leave the rest in the box with a hole in it?


    • Kevin,

      Just to clarify, solitary bees like masons (Osmia) do not live in hives. A hive is a man-made structure that houses social insects, whereas masons are solitary cavity dwellers. I’m clarifying so that other people reading this are not confused by it.

      Now, to answer. It’s too bad that some bees had already emerged. That is not a good sign because you don’t know how long they’ve been out of their cocoons, but they have not been able to eat or drink during that time. You should leave both the cocoons and the emerged bees in the box with the hole in it, and mount that box close to the mason bee house. You might also consider putting a shallow dish with sugar water within a few feet of the box to give those early bees something to eat. Be sure to put rocks or marbles in the water so the bees have something to stand on.

  • Hi,

    I put out the mason bees after our last snowfall…(it’s in the 70’s now) with flowers all around, bee clay at fence, and a plate of sugar water…

    I haven’t seen the bees in 2 days.. Do they always come back to the house? Do you think they just moved on?
    What do you think I should do?


    • Kevin,

      You say you put them out after the last snowfall. How long ago was that? Mason bees nearly always come back to nest in the same area where they emerged. Did you see many out and about earlier? Did you see any females filling tubes? I can’t imagine them going anywhere very far. If they are alive, you should be seeing them, unless they’ve been active for quite a while. Also, I don’t know were you live, so I can’t get about the climate.

      • I put them out about six days ago after the last snowfall. Temps are now in the high 60s low 70s. I live in Monument Colorado. I haven’t seen any since I released them last Monday. I have bee clay… flowers and sugar water out below the tree and on the fence next to them….

        • Kevin,

          It seems to me that you should be seeing the bees flying and mating near to their box. It is possible the cocoons weren’t properly stored and that they were not in good condition when you received them. Personally, I don’t favor shipping mason bees. I just put out mason bee housing and it soon fills with local bees that are adapted to my area. If your bees have perished, leave your housing in place anyway in the hopes you attract some locals.

          • Thanks…

            I received the mason bees from two different companies and when looking inside the Box they came in all of them except maybe three out of the 20 broke out of their cocoons……

            Oh well ….. all I can do is leave it up and hope for the best


            • Kevin,

              They should have been still in their cocoons when you received them. Don’t buy from those companies again.

              • They were in cocoons….by the time I put up the box to let them out they broke out of their cocoons.

  • Hi…

    I live in Monument Colorado dot dot dot dot Our last snowfall was last Saturday and then we have 65 degree temperatures by Monday. I put them out in the late morning on that Monday and we’ve been having very warm temperatures ever since all week. I saw them in emerge on Monday afternoon but periodically I go up and look and see if there’s any be activity and I don’t see any…

    I put out the bee nest last week…. flowers are all around and even a plate of sugar water with rocks in it. I also purchased be clay to put below the tree….

    Can’t understand it


    • Kevin,

      If you saw some emerge and then no more, perhaps they died. Sometimes, though, if they were stored in a really cold environment, it takes them a couple weeks to emerge. Maybe the outside ones emerged because they were warmer, but the inside ones are not yet ready. Be patient. There isn’t much more you can do but wait.

  • No Gary,

    I put them out about six weeks to two months ago and they all emerged, flew away and never returned. I don’t see any in my garden this year. I released between 30 and 50 from their cocoons. I have flowers out in the garden. Almost all of them are pollinator flowers…..

    Pretty disappointing.


    • Kevin,

      That is strange. According to Oregon State Extension, mason bees have a flying range of 100–300 feet, which means you should have seen them around. Are the flowers in your garden suitable for mason bees? Do you have fruit trees? Did you see other bees on your flowers? Where the cocoons close to the nesting blocks? Also, six weeks to two months ago is really late, about May 5th through 19th. I think they like to be out by mid-March.

      • The cocoons box was right on top of the honeycomb cocoon nest… I had put flowers around the side fence which is only 6 feet away. My pollinating flowers are only 50 ft away. No other bees are around..

        • Kevin,

          No other bees make me very suspicious, because if the flowers were attractive to pollinators, you would get some types of bee interested. I’m wondering if maybe the flowers are highly inbred or perhaps hybrids? Those often do not attract pollinators. The best pollinator flowers are heritage breeds, open-pollinated, and not bred to have special colors or extra petals. If you saw no bees on the flowers, I suspect the masons were forced to go elsewhere.

  • I would have to agree with Rusty. It sounds like they moved on to greener pastures. No bees hanging around means there’s no quality pollen nearby. Hybrid flowers are not good at producing pollen, and won’t attract any bees.

    Trees that generate pollen (our Linden attracts a huge swam every summer) are quite good. If your garden has vegetables such as squash, that should attract them, too.

    I’m sorry you didn’t get to keep them around, but there’s always next year! We are all learning as we go.

  • I live near a headland along the the north central coast of Oregon. We get strong south and southwest wind driven rains all winter long. I bought a bee box with a roof overhang but I worry that it is not enough to protect the box from the rains and I want to know if the wind driven rains will be too much for the bees to winter over. I would like to leave the box out all year long. This coming spring will be the first time I will hang a bee box so I am planning ahead. Thank you.

    • Ellen,

      Because we get so much rain, I take my native bee boxes in during the winter. They shouldn’t be kept warm, just dry. So I keep mine in my garden shed. Anyplace that is unheated and dry should work. I set them on a shelf for the winter and then put them back out in about March.

  • I’m new to this. Does my bee house have to be mounted, or can I just place it on a brick walk facing south or in the flowerbed itself? I assume that if it’s been out all winter that the tubes will have to be replaced at some point? When would that be? Midsummer? I live in northwestern Illinois, about 50 miles from the Iowa border.

    • Faith,

      You can place the bee house on a brick or in a flower bed, but it needs to not wiggle or move once the bees get started with nest building. When the tubes need to be replaced, you need to put them in a hatching box in spring so the bees don’t go back to them. Or you can harvest the cocoons out of the tubes in fall and put the cocoons in the hatching box in spring. You can’t do anything in mid-summer or you risk damaging next year’s bees.

      • Hi I live in a forested area and put a bee house out last year and forgot about it. It was a busy place with bees this spring. I want to leave the house out all winter and let nature take its course, but will it get to a point I need to clean the house or change it for new? If so, when is the time to do that?

  • Hello. This is my second year. I have my cocoons in small boxes in the fridge. Males and females are separated. I am in Northwest Washington. The bee house I built has an attic. I plan on putting a piece of cardboard in front of the attic to protect the cocoons in the boxes with a small hole in it. Do you have any suggestions that would improve this plan. I have two bee blocks that I made and I plan to build more to hang from the bottom of the bee house for expansion. Thanks. Happy beekeeping

    • Robert,

      No improvement. I find that they do best in full sun, though, so the sunlight shines clearly though the hole.

  • Hi Rusty,

    I live in Boulder, Colorado and received several mason bee houses for Christmas to place in my garden in March. Happy to pollinate. I understand they will be inhabited by local mason bees that will make their cocoons in them. Now what? Should I plan to keep the cocoons over winter, become a “beekeeper”, or just let nature take its course with the bee houses?

    • Jackie,

      It depends on how involved you want to be. You can just leave them outside and see if they make it from year to year, or you can be proactive by harvesting the cocoons and keeping them refrigerated. People do it either way.

  • If I make the overhang on the mason bee house wider so the rain doesn’t get them wet, would this affect the bees adversely? The overhangs on the roofs of the mason bee houses seem so narrow, 1 inch or so. Could I put a 3 inch overhang onto the bee house? This is my first year, so I appreciate your website.

    • Anna,

      A three-inch overhang sounds fine. I tuck my bee houses under the eaves of my shed and that is about 18 inches. It’s never been a problem.

  • Just got my mason bees and house mounted on Saturday, 4/7/18. Day time temp has varied from 55 to 68 since I mounted the bee house. I have two 6″ tubes of male and two 6″ tubes of female bees. I’m looking at the forecast and were in for a cold snap, day time temps in the high 40’s and night time temps in the high 30’s. My cherry tree is in full bloom and I am worried that the mason bees won’t hatch in time. Should I be thinking about hand pollinating a 4 year old Rainer, Bing and Chelan tree.

    • Jim,

      You can hand pollinate if you want, but unless you go crazy with pesticides, there should be plenty of early cold-weather bees out there pollinating your trees. Most of them are really small, about the size of fruit flies, so you may not notice them.

      As for the mason bees, they generally should be put out around March 1. The males hatch first by a few days, and then the females. Sounds like yours won’t make it for this year’s cherries.

  • We’re hosting a summer event for youth that is focusing on skilled trade employment fields including carpentry and agriculture. We’re thinking of having the participants build mason bees houses for a project since it will tie together both those fields nicely into a fun hands-on project. Our event isn’t until the middle of June. Is that too late for participants to set their completed houses out? Since we’re not supplying them with bees, are there some strategies to successfully attract native bees? I’d like to give the participants enough information on what to do and how to do it so their successful and more likely to continue. Any information is appreciated. Thank you!

    • Rhonda,

      Pollinator houses with tunnels attract a wide variety of bees, only some of which are mason bees. Although most species appear in early spring, tunnel-nesting bees also appear in summer and early fall. So you may get some bees after June. Probably not as many, but some including leafcutting bees, summer masons, and ceratina. If you want a wide variety of bees, you need to provide a wide variety of hole sizes from about 1/16 of an inch up to about 5/16 in 1/16-inch increments. Place the completed houses in a sunny but protected location near to flowers, a water supply, and a source of mud. Each location is different. You may get a lot of bees or none; it’s hard to predict.

  • I too have been raising solitary bees for about 8 years now. I have used rolled up copy paper (plain white paper) for nests and have even drilled into dead stumps. My preferred method is using 2x4s. I like to drill 3, 3/8 inch diameter holes that run 8 inches deep. My boards are about 10 to 12 inches long.

    My bees emerged late this year (south of Denver), some time around mid June. My elevation is 6200 feet. Last year they emerged around May 1st. I don’t know why they were a month late this year. When I first started doing this in northern Wyoming, my bees emerged around May 1st. I don’t have “houses” per say, just 2x4s on the back porch. They do get preyed upon occasionally by spiders and other insects but I try my hardest to protect them. Bees are my insect “children” Ha!

  • I ordered 25 mason bee cocoons. I have them in my fridge. Do I put them in a tube and put then in my bee house? If so how many in a tube.? They don’t seem to be sexed. Do we put mud in the front of the tube? Thank You, Gloria

    • Gloria,

      No, you do not put them in the tube or use mud. Just put the tubes in your bee house and put the cocoons in a protected spot close to the tubes where they can emerge when ready. I recommend you put the cocoons in a little box with a hole on one end aimed at the sun. After they emerge from the cocoons, they will go though the hole to the outdoors.

  • I’m a newbie to mason bees but am excited to try them in the community garden I manage. I have a couple of mason houses coming with all the same hole size. I’m in MN so was thinking to install as soon as possible. Any harm in that? Also, next year after emergence, is that the best time to clean out the holes for the next cycle? Thanks, this blog is great!

    • Dan,

      That doesn’t really work, because even before they all emerge, others will have started refilling the empties. The best thing to do is to put the cocoons or the complete straws in a hatching box (also called an emergence box) and put out new tubes for the next generation.

  • I hope someone here can help me. Last summer I noticed some bees going into brick holes on our house. I’m a native gardener and wanted to help them out so I purchased a mason bee house with cardboard tubes. Within days all the tubes were sealed up with mud. The tubes stayed sealed through the remainder of summer until now. I did not brings the tubes inside for winter. I noticed a few days ago that most of the tubes now have holes on the ends which appears that the bees have come out for the season. Can I now remove these old tubes and put new ones in? Am I too late? I don’t want the bees to reuse these older tubes and have disease issues. There isn’t much info on the internet on how to care for houses/bees if they are left out all winter. Please tell me what I should do next.

    • Erin,

      In most cases leaving them outside is fine. Zillions of these bees live in the wild and no one takes them in. The instant the bees emerge, they start filling the tubes again, so it’s best to use an emergence box. In late winter, you put the tubes or cocoons in the box with a small hole in it. When the bees emerge they leave through the hole but are reluctant to go into a dark place to look for a nest, so they don’t. So basically, you are too late for this year. However, tubes should be replaces after two or three years, so I don’t see any issues here.

  • I would like to add one additional comment. I just checked the tubes outside with a flashlight and I can only see 1 bee inside an opened tube. The other open tubes are too difficult to see inside. Should I move these tubes to an emergence box? If so what please explain what kind of box this would be and where I should place in my yard. Thank you!

  • Hi Rusty. I posted a question here last night but it has disappeared. Anyway let me try again. I left my mason bee house out over the winter with all the tubes being filled. I’m here in MI and the weather has been really up and down lately. I checked the tubes last night with flashlight and most are open but still a few sealed. Am I too late to add new tubes to this house? Where should I move the remainder of the filled tubes so the rest can emerge? How do I know if anyone is using the old tubes if there is only a tiny opening in the one end? Would the bee clear out all of the old mud before reusing?

    • Erin,

      Unless you’ve kept track of every tube, it’s hard to tell which are old and which are new. I would leave them alone at this point.

  • Hi, we have one of the oval bamboo bee suites. We are asking is it ok to use cedar shingles to cover the bee home from rain, or will the cedar upset the bees? Thank you sooo much, be having wonderful moments ???

  • Rusty,

    We just received a mason bee house as a present. I live in southwest Connecticut and it’s mid June so I’m assuming that it’s too late to put it up this year for mason bees. Please correct me if I’m wrong.


    • Dan,

      It’s too late for early mason bees like Osmia lignaria or Osmia cornifrons, but it’s not too late for the summer mason bees that are just starting to emerge. You may also get leafcutting bees in the summer, and sometimes small resin bees. I would put it up and see what happens.

  • Hello Rusty-

    I enjoy your website and could use some help and want to understand what went wrong with my mason bee housing.

    I had purchased 2 new mason bee houses, and put them up early spring. All was progressing very well, and the majority, if not all holes were ultimately filled and capped with mud. I left the boxes as is, did not touch them, did not protect them with any netting or chicken wire (did not know I need to protect them), and then one day (around end of May/early June) I noticed all the mud capped tubes, and I mean every single capped tube, was open, and does not appear anything is inside them.

    Something got to them and ate them???

    While researching, I am learning about the wasps and other predators. I’m thinking it might have been a bird since all the tubes were opened in such a short period.

    I am very sad and do not want to make the same mistake next year. What are your thoughts as to what happened and what I can do better next time.

    Thank you, Debbie

    • Hi Debbie,

      It’s hard to know who got them without actually seeing it, but it could be a bird or large insect. It could even be a small rodent. I now take my tubes inside as soon as nesting starts to slow down. If there are some stragglers, I leave a few tubes for them, but I put the rest where they can’t be attacked.

      If it’s birds, you can put wire netting around the mason bee houses. Poultry netting will work for most birds, but sometimes a smaller mesh works best, depending on the kind of birds you have. If it’s tiny rodents, you may want to use 1/4-inch wire mesh. You may have to experiment until you figure out what’s getting them.

  • Thank you for your reply Rusty. Now I have another question-I am watching the mason bee house carefully and notice it’s being used by leafcutter bees, since I see the leaf cappings.

    Although it’s not nearly as busy as in the spring, the holes that are capped are now being eaten as well, as the days pass I see holes in the leaf cappings, or the leaf cappings are gone, and I see leaf pieces strewn below.

    I notice very small, I call them gnat, flying about, not sure what they are and if they are going in the tubes, some ants going in the tubes, and small blackish bees (?) going in, sometimes with pollen on its underside, and other times going in and pushing the pollen out of the tube and ultimately flying away with the larva (?). Wish I had pictures, wish I knew exactly who is the culprit.

    The ants I have some ideas to try. But how do I cover and protect the house and tubes from these types of flying predators if the solitary bees are still using them? It seems are soon as the tubes are filled, some type of flying predator comes in. Thank you again.

    • Debbie,

      As soon as the holes are capped, I take the tubes (or the whole pollinator house) and store it in a garage or shed. Lots of things can attack the filled holes, including tiny wasps the size or fruit flies. Also, larger wasps, ants, and birds are common. Sometimes you have to take down the housing even when some bees are still actively using it in order to protect the majority. The few stragglers will find other places in the environment to use.

  • Hello Rusty,

    I just purchased a mason bee house from my local farmer’s market. I live in the Maryland and want to know when is the best time to put it outside for the bees to use. Is August too late, or should I wait until the spring?

    • Stephanie,

      I would wait until late March. You could possibly get some late summer bees, although in my experience you are much more likely to get them in spring.

  • Rusty,

    Hello there, this is my first year with bees in Denver and I received my first load of bees today in a wonderful snowstorm. I looked in the box and they are already moving around. I was thinking of putting them out in the bee house but it’s going to be cold for the next two days, should I bring the house inside and put them in it? Just wondering how long they can remain in the box before they get cabin fever.

    • Roger,

      You can leave them in the package for several days, just make sure they have syrup and the jar/can hasn’t run dry. If you install them into their final home inside the house, you will have to deal with the problem of moving them later.

  • I have enjoyed reading your site, really interesting, thank you!
    I have a question please. I have noticed solitary bees emerging and sleeping and working in and around my insect house. It has been warm and sunny here in March (The Netherlands). But there will be a temperature drop to minus 2 Celsius in the next few days. The bees are sleeping in the small holes in the insect house overnight then emerging to work at sunrise. I am concerned that minus 2 Celsius will be harmful to them. I am not sure what to do for the best to help them? Any suggestions gratefully received. With kind thanks, Glynis Brown

  • This is our first year with mason bees. We purchased a box of mason bee cocoons and set it out 2 weeks ago. The bees have been very active and almost all of the tubes in the house are filled. This has happened a lot faster than we expected. Should we set up a second house, or put out more tubes?

    • Jennifer,

      You can do either, or you can let them nest naturally in the surrounding area. The nesting behavior will gradually decrease and stop altogether about 6 to 8 weeks after it began.

  • It’s late April and no bees have emerged. Have I lost them? I kept them in the garage for the winter and put them out early April. I live in Western WA.

    • Hi Janis,

      I’m not sure what’s going on with the masons this year. I had a little burst of activity about a month ago when about 12 emerged. The rest of the tubes are quiet with the bees still holed up inside. It could be the weather, although I don’t know for sure.

  • What happened?

    I learned about solo bees this spring. I drilled holes of various sizes in a section of log and mounted it in a fence post in my Detroit area yard in April. By mid May, half the holes were filled with plugs. I work during the day and didn’t often get to observe progress, but last week I saw a bee at a hole and I thought she was sealing it. Now a week later almost all the holes are open again. I didn’t expect hatching until next spring.

    What is going on here? Do some bees lay eggs in the spring and hatch in summer? (That was not my understanding.)

    Should I leave this log out, or scrap it and start over?

    (There are plenty of small bees in my yard, but I have no idea if they are customers of my bee house or not.)

    • David,

      Although it is not common, some bees do have two generations in a year. But there could be a number of things happening in you your bee nest. Predation by birds or other insects is one likely answer, as well as parastic insects such as wasps. You would probably have to see the action to know for sure.

  • May I place my mason bee condos in my greenhouse? It has a temperature control system that automatically opens and closes a few of the glass panes to keep a consistent temp. We are on the central Oregon coast about 15 minutes inland of Newport. We are growing winter heath and heather in and around the greenhouse to provide local bees winter sustenance.

    • Patrick,

      Mason bees should be stored at about 40 degrees F. If it’s too warm, they will use up their fat stores and may emerge early.

      • Hello Rusty

        What are your thoughts on this?

        After all my new paper straws and first-time used hollow plant tubes were filled and capped, I moved all of these into my unheated detached garage for storage until next spring. There were around 75 to 100 tubes. I had placed them in a paper bag and noticed that there were little bugs inside. I then wrapped the paper bags in towels after I try to brush away any of the little critters. I was careful not to jostle the tubes in any way. Long story short, they sat there for the whole winter until I brought them out this spring. A vast majority of the capped tubes remain capped. No bees emerged. Well, some did, but only about 20% of the tubes. When I did open up one of the tubes, it looked like there was still pollen and as if the egg never hatched. What are your thoughts as to what happened? That is a lot of bee loss. And I am perplexed. Thank you. Debbie Barrett.

        • Debbie,

          Yes, it is a lot of bee loss, but many things can go wrong. If you saw a pollen mass and an egg, it sounds like the egg never hatched and there’s no telling why that might be. Were a lot of them like that? Perhaps the female that laid the egg was not properly mated. Usually, overwintered bees that die do so in the larval or pupal stage.

        • It takes very little physical disturbance of the nesting tubes during larval development, less than one might expect, to disrupt their feeding and cause death. I’ve experienced a surprising amount of this from a curious person just moving the groups of reed tubes that were in a box a little in June. Try to leave them exactly where they are outside until late Sep or so. You can also reduce parasitic wasp and carpet beetle depredation by attaching a piece of fine nylon mesh (stocking or paint strainer material) to the front of your box to keep these pests out, right after the females finish their work and aren’t flying anymore. Do it gently without jolting the box. A dead larva in a cell will be a small, brownish, dried-up thing. Maybe you saw some of those and thought they were eggs. Doubt you’d be able to see an egg many months after it was deposited.

          • Cal,

            Just my two cents here, but if you use mesh to prevent parasitic wasps, it needs to be extremely fine. Monodontomerus, one of the worst wasp species on Osmia lignaria, are extremely tiny. They go right through my net with the finest mesh.

            Also, if people see what looks like eggs, they are most often seeing larvae. Just like ant “eggs” are really larvae, so are the rice-like white young of wasps. The actual eggs go through the wasp’s ovipositor, so they are indeed very small, but the larvae are easy to see.

          • Thank you for your comments. After reading and learning more, I opened up some tubes, found cocoons covered with frass, so my initial thoughts as to what happened were incorrect. When I opened the cocoons, I found little rice pieces inside, which I learned were larva from parasitic wasps. I believe these wasps were what I saw in the paper bags where I stored the tubes for the season. Sad to know several hundred bees died as I had many long filled tubes stored for season with the wasps right in the bag with them. Presently, I am taking the tubes as they are filled and placing them front side up in a container in a mesh enclosure, which I will monitor for interlopers. I hear your point about how easily they can be jolted by moving them.

            • Debbie,

              Sounds good. Remember that some of the wasps are much smaller than a fruit fly, so your mesh must have a tight weave.

  • I have a bee house I bought from Costco. Looks lovely and this is the second season I have it hung. All the holes are filled with mud or grasses so I am hoping it is full of bees. I do not have time to harvest the cocoons and release the bees. I have had it sheltered in an outdoor shed over the winter. Can I just rehang it (now mid-March in CO) and let nature take its course?

  • edit to my earlier post:

    When I open up more tubes, I find the cocoons and cut them open, they have small rice like pieces inside. What happened and when?

    Thank you
    Debbie Barrett

    • Debbie,

      Things that look like grains of rice are usually the brood of parasitic wasps. What happens is the adult female wasp sticks her long ovipositor right through the cocoon (often right through the tube and the cocoon) and lays her eggs inside. These hatch, eat the bee larvae, and then grow into adult wasps. The wasps occur frequently in nature, but the populations get larger if there are lots of bee cocoons to feed on. This is one of the arguments against raising large number of mason bees close together.

  • I will harvest, clean and store my bee cocoons over the winter, but when I am ready to take them outside in the spring, what do I need to do? Do I just open the container they have been wintering in or do I put the cocoons somewhere or in something so they can emerge safely?

  • Dear Jen,

    A British lady here. Yes, I use a release box, it has a well-made area to put the tub of cocoons inside. The bees can make their way out as soon as they hatch. Even if you are not in the UK I have found all I need at Mason Bees UK. A wonderful resource and also for all the resources I need. If not able to buy from them, take a look at what they suggest. I have felt very secure in their experienced hands. Good luck!

  • Question: I have several bee homes I’ve drilled holes into and every three years I rotate these with new homes in seasoned wood logs. This works well. When my bees emerge, I’ve noticed white, bird-dropping-like deposits under the houses on my deck. Is this discarded cocoon material?

    • Gene,

      Cocoons of the Megachile bees, including masons and leafcutters, are firm, solid, and hold their shape. I think what you are seeing is just bee feces.

      • I had heard on a mason bee talk that the males scent mark and this was the light color marks we see. I cannot find this YouTube talk to clarify and had not heard anything like that before. Have you Rusty?

        • Debbie,

          That’s so interesting (things like this get me all wound up) and I will dig into it. Usually, we can’t see a scent pheromone, but if the pheromone is passed through the feces of the male that could explain the appearance. This is something I need to know!

        • Debbie,

          I just found this: “The white secretions that are often seen below the entrance to a mason bee house are most likely mud or clay mixed with glandular secretions from the female mason bee.”

          • Rusty & Debbie:
            This is interesting and explains a lot. Thank you for digging into this. I wonder if this excretion from the females last only a short period around the time they emerge and not later. Casual observations seem to make this a temporary episodic event since I do not observe this later in the foraging season. I should however keep a closer eye out on this.

            • Gene,

              Over the years, I’ve written a “s—load” about bee feces. Basically, bees do not defecate in their cocoons. The waste is held in their intestines until they emerge as adults and then they let it all loose. This would surely explain the drips and drops below an emerging nest of bees. Once adults, both male and female, leave the nest, they relieve themselves out in the field or in the flowers.The photo shows honey bee feces, but all bees are built basically the same.

              The question that intrigued me here, is whether the male feces could be laced with a mating pheromone. I haven’t found anything on that either way.

          • Hmmm…I’ve always thought it was bee feces. The male mason bees emerge first, and as soon as I start to see them hanging around their box, I see these small drops and splats of a light tan material. I can see it on the inside walls of the mason jar that I store my cleaned cocoons in also, if a few males emerge before I put them out in the bee house. The amount of this material increases dramatically as more males and then the females emerge. It seems to me that they may retain this in their hindgut until shortly after emergence, then they void it.

            • Cal,

              It’s definitely feces, but does the male version contain a mating pheromone, something injected just before it leaves the body? I’ve never heard anything like that, but it’s possible I suppose.

          • By the way, this comment was credited to a Xerces Society document, but when I found the document I couldn’t find that quote in there. I’m skeptical.

      • Thanks Rusty. I did give that a thought but wondered why it would be concentrated near their “home” and only soon after they emerge from their tubes and not much thereafter. Now, however, I have to look into bee scat.

        • Ah ha! Although I did not find the video where this was explained, I did return to the source and found this about male scent marking:

          What are the brown markings on the white tube/house?

          “Those are scent marks left by the emerging male bees. Male mason bees will hatch a few days to a few weeks earlier than female mason bees. As soon as they hatch, they will scent mark their surroundings with a pheromone marker so that they will know where to return to find the females. You will periodically see them reenter the white tube looking for hatched females.”

          • Interesting. The brown marks are definitely bee feces. You can’t see pheromones. They are misted into the air by scent glands. Just like the odor of flowers or the scent of bacon cooking on a grill, you won’t see patches of smell anywhere. Now, I concede that mating odors could possibly be included with the feces, but the info I’ve found so far says otherwise.

            If you keep honey bees, you know that bees leave feces all over the place. You will also know that you can’t see honey bee nasanov scent or mating scent or brood pheromone. This is just basic bee biology that is shared by most species of bees.

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