Tag Archives: mason bee

Guide to building mason bee houses

DIY bee hotels can be filled with (1) routered nesting trays, (2) drilled wood blocks with paper inserts, (3) drilled wood blocks without inserts, or (4) hollow stems. Or, like house in the photo below (construction details here), all four types — each type has pros and cons.

Below are some links to DIY houses I admire.

The key is to build the hotel so that everything can be removed to make room for fresh nests each year. I.e., you replace everything each year except the house itself. Note: you can reuse drilled blocks of wood (or sections of logs) if you re-drill them (to remove debris) and then kill any residual mites and pathogens by briefly submerging in bleach (or baking, or freezing). Similarly, nesting trays should be cleaned and sterilized (Crown Bees has nice video of that).

If you want to read articles on hotel design, please refer to bibliography I’ve compiled at bottom of this page. If you’re lazy but want a mason bee house ASAP, just buy one: here’s a draft listing of companies that make good mason bee houses. Here’s a guide to avoiding death-trap bee houses.

If you want to see pics of all the beasties that show up at my mason bee houses, I have them all on iNaturalist.

Where to buy mason bee houses

The following companies sell bee houses that have deep (approximately 6″ / 152 mm) nesting holes, have disposable or cleanable components, have protective roof overhangs (usually), and are not suspended by a string. If I’ve missed somebody, send me a note and I’ll update this post.

Houses with replaceable nesting tubes, reeds, or blocks

Houses with stackable, cleanable nesting trays

Houses with observation windows

There is no perfect house, so do a little research with local bee experts to see what might be best for your area. Also, no single house is going to attract all types of bees. Figure out what type of bee you want and then find a house that suits it. Personally, I’m a fan of having several, smaller houses so that I can situate them in different parts of the yard. I also like to think that this separation reduces the ability of parasitic wasps to lay eggs in the tunnels. I.e., if you have a hotel with hundreds of holes, that makes it very easy for parasitic wasps to go hole to hole.

I don’t see the need to buy the bees themselves. In fact, sending animals in the mail can result in their deaths when postal trucks heat up. More broadly, sending bees from one area to another might mess with local adaption (i.e., bees from one area might not have evolved to do well everywhere) and also introduce hidden pests and diseases. If you put out a good house, in a good location, and have mud and native plants … the local bees will find you.

Here’s a guide to avoiding death-trap bee houses that are for sale at most garden centers. If you’re handy, you can also make your own (it’s fun).

The horrors of mass-produced bee houses

Here are some reasons why cheap mason bee houses can end up hurting bee populations. I live in Pennsylvania (USA), so some of the issues might be specific to areas with high heat and humidity. And to the species that live here, of course. Check with your local authorities for more detailed advice.

1. Nesting blocks, tubes, reeds are not removable

Glued nesting materials is the number one reason why most commercial bee hotesl can become death traps. Because the nesting material cannot be removed and cleaned (or just thrown out), over time there will be an increase in the population of parasitic wasps, parasitic bees, parasitic flies, kleptoparasitic mites, fungi, bacteria, and viruses. And you typically won’t see these dangers because the solitary bees will still use the hotel (they can’t help themselves). But inside, out of view, their eggs, larvae, and pupae are probably dying at a much higher rate than when you first installed the house. And if you leave that house out for years and decades, that pest-ridden hotel might be doing more to increase the population of pests than solitary bees.

Hundreds of Krombein’s hairy-footed pollen mites on a mason bee. Image by @GeeBee60.

Ideally, empty out the house every year or two and give it a good cleaning. You can do this by removing all the filled nesting tubes at the end of the season (e.g., October) and storing them in an unheated garage or shed. Then, in the early spring put these nests inside a cardboard box that is equipped with a small exit hole — so bees can escape but can’t re-inhabit the nests. Finally, once everyone has emerged, clean the trays (brush, wash with bleach), re-drill holes (for blocks), and throw away reeds and paper tubes. While all this is happening, equip your (cleaned) house with fresh nesting trays, blocks, paper tubes, reeds, etc. All of this can’t happen, of course, if everything is glued in place.

If the above sounds like way too much maintenance, perhaps don’t buy a mason bee house. Get a garden gnome or a gazing ball.

2. Inadequate instructions

Even if you buy a good bee house and generally know things about the needs of solitary bees (they need a supply of mud or leaves, lots of native plants, etc.), you can still benefit from detailed instructions from somebody who thinks about solitary bees all day long. There are a lot of tricks. All of the cheapo houses lack such instructions. Most have no instructions at all, so you’d never even know about the parasites and such that will likely move in if you leave it out for a few decades.

3. Nesting tubes open at back

If holes aren’t capped in some way at the back, parasites can easily gain entrance. Mason bees will plug the back with mud but it’s best to have a wall.

4. Reeds or holes with large splinters

Sharp edges inside the holes can snag and tear delicate wings.

5. Stems blocked at front

In the majority of cheapo houses that use bamboo, many of the sections are blocked off near the front by an impenetrable node. This is just another sign that the makers of the mason bee house could care less about bees. They just want your money.

6. Roof lacks overhang

Mass-produced mason bee houses are designed to be as compact as possible so they can be packed and shipped efficiently from factories in Asia. This usually means that they won’t have roofs that protect the nest entrances from water. That’s bad, especially in rainy climates. Moisture causes larvae to rot and also seems to cause kleptoparasitic pollen mites to flourish (that’s bad).

7. House attaches to tree with string or hook

Mason bees start their lives as eggs on top of a mound of pollen, and houses swinging in the wind could cause them to fall off or be crushed by moving pollen balls (when too dry they can shift). At least that’s the word on the street — I don’t have an observation window on my bee hotel so I can’t confirm this by hitting it and watching them fall off and die. Perhaps a more important reason to keep the house stable is that mason bees likely find it challenging to land on a moving nest. Again, they isn’t a literature documenting this problem but I’ve witnessed many mason bees (and related Megachilidae) that simply cannot stick landings on even non-moving nests. If you have a mason bee house that is design to hang, just get creative and attach it somehow so the bees have an easier time landing.

8. Nesting material is impermeable to water

Like anything that’s alive, mason bee eggs, larvae, and pupae produce water from respiration. When that moisture can’t escape the bees are likely more susceptible to bacterial and fungal pathogens. Plus the pollen rots. So avoid houses that use plastic straws or glass tubes. Some say (e.g., The Honeybee Conservancy) that bamboo is too impermeable but that might depend on where you live. If you are concerned about humidity, opt for paper/cardboard tubes (thick paper straws might work, too), hollow plant stems, or holes drilled in wood. Unfortunately, using paper and cardboard tubes might make the bees more susceptible to parasitic wasps that can oviposit (or chew) through thin-walled nesting tubes. There are trade-offs like all things in life.

9. Nests are too shallow

The house pictured at the top of the page is approximately 2″ deep, and that could lead to most of the progeny being males. In nature, mason bees lay fertilized eggs (which develop into females) at the backs of long nests, then pack the front with unfertilized eggs (which develop into males). This means that houses with short nests can end up being primarily nurseries for worthless guys (sorry, guys). If you want a house that can generate an ecologically useful proportion of females, buy houses with nesting tubes that are approximately 6″ (152 mm). Shorter tubes are OK for smaller bees, it seems. That said, bees will use even 1/2″-deep holes.

10. Too many nesting units

When thousands of mason bees are living in close proximity, parasitic insects and mites can easily find every nest. If your heart is set on a mason bee mega-complex, just be extra sure that all components are truly cleanable or disposable. It’s also critical to actually clean it, too, so don’t buy it if you’re the type that doesn’t like to do that sort of thing.

These look soooo cute, but if ALL the blocks are left in place for multiple years they become towers filled with bee parasites.

11. Honey bee shown on packaging

This is a minor concern, but it bugs me. A photograph of a honey bee on the label is a likely sign that the house is probably not up to code.

Mason bee house with honey bee drawing

Flow chart for making buying decision

Here’s a summary flow chart to print and keep in your wallet so you’re prepared when you see something adorable. Or print and give to that shop owner who carries trap houses.

“OMG I own a death trap what should I do?”

If you have a cheapo mason bee house that saddens you, don’t do anything rash. Just leave it up and let your current residents do their thing. But at the end of the season, after all the holes are filled, put it in an unheated shed or garage for the winter (so that birds don’t feast on the pupae). In early spring, put the whole house inside of a cardboard box (here’s an image of durable emergence box). Poke a small hole in the top or side so that emerging bees see the light and escape through that hole, and then set it outside in a place where it will stay dry. After all the bees finish emerging (summer), throw out the house. Or, better, burn it and record a video of the fire. Then post the video online to bring needed awareness to low quality mason bee houses. If you have a good photograph of a burning mason bee house, I could use one right here.

“I want a cute bee house but not the commitment”

If you absolutely want the cute look of a bee hotel but don’t want all the maintenance fuss, here’s a trick: print this photograph onto a large piece of paper and mount onto a board. To make it last, laminate or apply a coat of clear varnish.

Free bee housing for the lazy!

The BEST way to encourage lots of native bees in your yard is to just stop overdoing the yard work. Make a pile of stems from last year’s perennial garden somewhere in yard, and they’ll naturally break apart and be found by solitary bees — Monarda and Asclepias are some of the many perennials that are hollow. And leave dead trees (or logs) so that boring beetles do their thing and leave nice tunnels for the bees. Finally, leave some patches of your flower beds unmulched so that ground-nesting bees have some ground.

More information


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Don’t let the above discourage you from owning your dream house: here’s a draft listing of companies that make good ones. Or, make your own.