Tag Archives: hymenoptera

Guide to building mason bee houses

DIY bee hotels can be filled with (1) routered nesting trays (with our without with paper inserts), (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.

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 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).

Below are some links to houses I admire.

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.

Questions?

Or just want to show off your mason bee house? Email me.

If you post your house pic online and want to tag me, I’m @colinpurrington on Twitter, @colin_purrington on Instagram. 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 or individuals sell bee houses that have 6″ (152 mm) nesting holes, have disposable or cleanable components, have protective roof overhangs (usually), are not suspended with string, and do not use bamboo.

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 houses. Then you can situate them in different parts of your yards, a separation that reduces (slightly) the ability of parasitic wasps to lay eggs in the tunnels. Plus with several houses I can vary the diameter of the nesting holes. I’m increasingly fond of the super small wasps and bees that like to nest in holes. If you can’t find something perfect, make it yourself.

Houses with replaceable nesting tubes, reeds, or blocks

Houses with stackable, cleanable nesting trays

Houses with observation windows

If I’ve missed somebody, send me a note and I’ll update this post.

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. Nests are too shallow

The house pictured above is approximately 2″ deep, too short to be much help in raising bee populations. 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 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) or longer. That rules out almost all houses on the market these days. This advice is for bees that nest in 1/4″ or larger holes; shorter tubes are OK for smaller bees, it seems.

2. Nesting blocks, tubes, reeds are not removable

Mason bee hotels can quickly becomes feeding troughs for dozens of species of parasitic wasps and flies, kleptoparasitic mites (they eat the pollen, image below), and various fungi and bacteria. You wouldn’t know this unless you studied the goings-on carefully, though. It turns out that many bee species will reuse uncleaned houses for years and years. But just because they keep coming back doesn’t mean it’s a particularly safe hotel for them.

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

Ideally, empty out the house every year and give it a good cleaning. And during the winter the filled nesting tubes or blocks should all be stored in a safe, unheated garage or shed. And then in the early spring, those nests should be placed inside a cardboard box that is equipped with a small exit hole — so bees can escape but can’t re-inhabit the nests. Once everyone is emerged, clean the trays (brush, bleach), re-drill holes, and throw away reeds and paper tubes. While all this is happening, you will need to 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, don’t buy a mason bee house. Get a garden gnome or a gazing ball.

3. 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).

4. 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 will become susceptible to bacterial and fungal pathogens. So avoid houses that use bamboo, plastic, and metal tubes. Yes, bamboo is pretty much impermeable to water when mature. You want, instead, paper/cardboard tubes, hollow stems, or holes drilled in wood. I live in Pennsylvania where it gets really humid, so this is a concern for me. 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. Again, check with local authorities to see what’s best for your area.

5. 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 can cause them to fall off. Starving to death so close to a bed of food is a terrible way to die. Also, mason bees have difficulty landing on a moving house. The latter issue seems more important, at least for the bees I get in Pennsylvania. Only get houses that attach with screws.

6. 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.

7. Reeds or holes with large splinters

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

8. 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.

9. 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.

10. 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 all parasites and such that will likely move in if you leave it out for a few decades.

11. Honey bee shown on packaging

A photograph of a honey bee on the label is a sure sign that the house is probably not up to code. Companies that don’t know what a mason bee is shouldn’t be selling mason bee houses.

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.

Question?

Email me.

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.

If for some reason you want to see my Twitter thread on this topic, here you go.