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).
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. Some of these sites also sell cardboard and paper inserts, routered nesting trays, etc.
Here are some reasons why cheap mason bee houses can end up hurting bee populations.
1. Nests are too shallow
The house pictured above is approximately 2″ deep, far too short to actually help 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 nurseries for worthless guys (sorry, guys). If you want a house that can generate an ecologically useful proportion of females, only buy houses with nesting tubes that are approximately 6″ (152 mm) or longer. That rules out almost all houses on the market these days.
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.
So you absolutely have to 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.
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. Only get houses that attach to walls 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 houses that use bamboo, a good proportion of the sections are blocked off near the front by a 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. Just like bed bugs in a large hotel. 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.
10. Honey bee shown on packaging
Companies that don’t know what a mason be is shouldn’t be selling mason bee houses. It’s a sure sign that the house is not up to code.
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.
If you are about to buy a house but are nervous it’s death trap, email me a pic.