Tips for 5-Star Wild Bee Hotels
Bee hotels are fast becoming a backyard staple. Similar to birdhouses, bee hotels provide vital and missing nesting habitat. In the wild, hole-nesting bees usually nest in holes in standing dead trees, fallen logs, and broken branches of bushes and large grasses. Wild hole-nesting bees are desperately searching for suitable nesting sites and we’ve seen them make do by nesting in the ends of old garden hose nozzles, openings in metal garden furniture, and even the hollow ends of wind chimes. But unlike birdhouses, we can’t just build bee hotels and leave them alone. Bee hotels need to be maintained and managed or they are destined to become slums for bees. Our bee guests deserve the best accommodations!
Opening our Eyes to the Real World of Bees
The bees that nest in bee hotels are really, really different than honey bees or bumblebees. We’ve all grown up learning about the social structure of honey and bumblebees and we’ve come to think that their lifestyle represents all bee behavior. The truth is, the world is home to 21,000 species of bees (and more are discovered every year) and a whopping 90% of bee species do not live in social structures.
Instead, most of the world’s bees live alone. We call this bee behavior and lifestyle “solitary” and every solitary bee is fertile. Solitary female bees are fertile queens and they have all the duty and responsibility to take care of their young. Each female bee has to gather pollen and nectar, build nests, and lay eggs.
Solitary female bees are gentle because they are too busy to aggressively protect their nesting site and they simply can’t risk their lives. Solitary bees will only defend themselves as a last resort, like when they are accidentally squished or stepped on. Many solitary bees have barbless stingers and rarely does someone develop an anaphylactic allergic reaction to their mild venom.
Solitary bees don’t live in colonies, they don’t build hives, they don’t make honey or wax, and they don’t form attack swarms. To understand the world’s bees, we kind of, sort of, have to forget everything we think we know about bees. Out of the world’s 21,000 + bee species, there are only 7 species of honey bees after all, and bees are as diverse as apples to oranges and pears.
To Build Great Bee Hotels, Get to Know Wild Hole-Nesting Bees
So, if 90% of bees don’t live in hives, how do they live? About 70% of bee species nest underground and the remaining 30% nest in cavities or holes in wood or hollow broken stems. Some hole-nesting bees like to drill their own holes and these are called carpenter bees. Large carpenter bees, in the Xylocopa genus, chew tunnels in solid wood and since it takes so much time to dig a good tunnel they reuse nesting homes. Small carpenter bees, in the Ceratina genus, prefer to chew tunnels in the soft pith of broken stems like in raspberry and blackberry canes.
Many hole-nesting bees are too small to chew their own holes in solid wood. Instead, they save time and energy by nesting in pre-made holes like old grub tunnels. Or they use the crevice in peeling bark and build just one wall along the bottom. Hole-nesting bees that nest in pre-made cavities come in a variety of sizes and it’s best for them to nest in a hole that is just the right size and depth for them. Examples of popular hole-nesting garden pollinators are blue orchard mason bees (Osmia lignaria) and alfalfa leafcutter bees (Megachile rotundata).
Most solitary bees have a short lifespan as flying adults. For example, male mason bees are only flying for 2 weeks, long enough to mate, and female mason bees are actively flying for 4-6 weeks. With such a short timeframe as adults, solitary bees do not make honey. This short lifespan also drives some solitary bees to have a short flying range from home, too. When they first look for a good nesting spot they may fly a few miles searching, but once they check into their new bee home they only fly a few hundred feet (about 100 meters) from their nesting site. Surprisingly, a big chunk of a solitary bee’s life is spent in their nesting site hibernating over the winter.
What’s Inside a Hole-nesting Bee’s Nest?
The female bee is building nesting chambers inside the nesting hole and she builds them in a series, all in a line. Of course, she starts at the back and each nesting chamber is provisioned with food for one egg, which is a mix of pollen and nectar called a pollen loaf. The female bee lays an egg that is firmly placed in the pollen loaf and then seals the chamber with a protective material to keep each egg safe as the next chamber is built. The protective material is either a wall between nesting chambers or it is a protective cocoon that the mother builds to encase the larva as it develops.
The protective nesting material depends on the species and when that species is active in the year. Many mason bees are active in early spring and they use mud, which is wet and workable for gathering. Some spring mason bees use chewed up leaf bits (called leaf mastic) or a mix of pebbles, mud, and leaves. Leafcutter bees build protective leafy cocoons from the summer’s abundance of soft, pliable leaves. Resin bees gather sap while it is warm and flowing in the hot summer months. Some bee species mix a few ingredients together and all bees protect their nesting hole with an extra thick layer of nesting material. This protective layer is right at the edge of the hole and it’s called a capped end. The materials used for capped ends and their texture gives us a clue to who built the nest.
After the bee egg is laid, it can either hatch and develop into a flying adult right away or go into hibernation, otherwise known as diapause. Bee larvae are usually white and they look like chubby grubs. Once the larvae eats its pollen loaf and has nothing left to eat it spins a cocoon and goes through the cycles of metamorphosis. Spring mason bee eggs hatch and develop over the summer and they hibernate as fully formed adult bees, which makes them ready to go as soon as the daytime spring weather warms above 55*F consistently.
We can easily and safely harvest blue orchard mason bee cocoons in the fall and take care of their sturdy, waterproof cocoons by storing them in the fridge. We’re learning more about how other wild bees develop in their cocoons so that we know when we can safely and easily harvest cocoons to ensure the bee’s health.
Many hole-nesting bees that are active in the summer need warm weather to incubate to finish developing. Some bee species are able to have more than one generation develop in the long summer season. For example, alfalfa leafcutter bees can hatch and develop right away and new adults are called second generation bees. This means that the leafcutter bees can spend even more time pollinating your garden and farm.
Pests and Diseases that Harm Bee Hotels
There are a lot of tutorials for bee hotels and their intentions are great, but one big piece of knowledge missing about hole-nesting bees is the fact that they struggle with pests, diseases, and predators just like any other creature. Man-made nesting holes are not the same as the nesting holes found in nature and the nesting holes of bee hotels are close enough together for common native bee diseases and pests to spread and overrun a bee hotel. To reduce and deter diseases and pests is easy, simply harvest cocoons and separate healthy cocoons from infected nesting chambers.
The three big problems that hole-nesting bees face are pollen mites (they eat the pollen and nectar loaf before the bee larva does), chalkbrood (a fungal infection that converts a larva into a mass of fungal spores), and parasitic wasps (gnat-sized wasps that lay eggs inside of healthy larvae). As you harvest cocoons, you can learn how to identify infected chambers and keep healthy cocoons safe. There are larger, more well-known predators like ants, certain beetles and birds.
Design Tips for Successful Bee Hotels
As experts with decades of experience raising hole-nesting bees, the following are tips for how Crown Bees would design and manage bee hotels. Some of the tips sound time-consuming, but in reality each step should only take a few moments. Our effort to do things right is well worth it since the UN has reported that 40% of the world’s insect pollinators are facing extinction. Our bee hotel’s wild hole-nesting bee residents are the bees that actually need our help.
1. Protect developing larvae. Plan your bee hotels ahead of time so that you can remove nesting materials as they are filled and store the filled nesting holes in a warm location. You want to keep nesting materials in locations that have similar temperatures as the outdoors, like a garden shed or unheated garage. Removing and protecting filled nesting holes in a fine mesh bag keeps the small parasitic wasps from being able to attack larvae. To protect a drilled block of wood, place liner inserts or rolled paper inserts (pinch the back end closed) into each drilled hole and remove and replace these as they are filled.
Keep an eye on the filled nesting materials. Parasitic wasps may have already attacked and they are able to develop into adults very quickly, you don’t want them to harm more larvae. Also watch to see if your bees are the type that develop in the same season they were laid and are ready to emerge.
2. Provide nesting holes in the proper size range, made of the right materials. Avoid bamboo and plastic straws, as these do not let the moist pollen loaf breathe. Many bamboo shoots are much too large for any North American bee to use. Nesting holes should be between 4-10 mm in size and should be about 6” long. Nesting holes that are too shallow will skew the sex range of next generation’s bees. Natural, locally available nesting materials are best. Crown Bees’ Pollinator Pack provides cardboard tubes and lake reeds in the right size range and they are easy to open for cocoon harvest.
3. Protect nesting materials from wind, rain, and birds. Build a protective outer structure that has a 2-3” overhang. If birds are attacking the nesting holes, use 1” wide wire cloth and bubble around the bee hotel. Do not install wire cloth flush against the nesting holes because this will obstruct the bees from entering. Bees need some landing space for approaching and taking off.
4. Avoid a hotel that is too large. While a bee hotel that is 4 feet wide and 6 feet tall looks great, draws a lot of attention and raises awareness to our bees, this size is much too ambitious and will become a burden to maintain. Provide bee hotels that matches what the area nearby the house can provide, for example, many flowering trees and bushes can provide more pollen than a meadow of flowers can. Also, think about the time that you can devote to cleaning and managing the bees that move in.
5. Location and a word about solitary predatory wasps. Orient the bee hotel to face the morning sun, as hole-nesting bees are cold-blooded and need the sun’s warmth to get the energy needed to fly. We know that mason bees prefer some afternoon shade and have heard that too much shade could actually attract solitary hole-nesting wasps. Solitary wasps are predators of garden pests and they fill nesting holes with caterpillars, aphids, and even spiders. Hole-nesting wasps are great beneficial insects that are a good indicator that your garden is balanced and supports all insects. Solitary wasp larvae are also white but their shape and skin are different from a bee, they are longer with large bumps and they feel waxy.
You might want to provide two bee hotels in your yard with each bee hotel facing a different direction. One house can face east and another can face southeast. We are curious to learn if bee species have a preference for orientation of their nesting house. You might also want to place bee hotels in your yard and one in a wild location, like a meadow or forest. A natural habitat could be home to a different mix of local wild bees that you could then introduce to your yard.
6. Harvest cocoons. After protecting and storing filled nesting materials over the winter, open materials and harvest cocoons in the early spring. If you can, organize and separate cocoons based on appearance and when their nesting holes were capped. When you incubate in a mesh bag, you have more control for releasing the bees outside. Incubating inside of the fine mesh bag also helps you reduce the release of the gnat-sized parasitic wasps.
Join the Native Bee Network
You can help us all learn more about our native hole-nesting bees by participating in a citizen science project. Crown Bees' The Native Bee Network is, for example, a way for gardeners and farmers to gather information and share it with other growers. Traditional scientific knowledge can tell us a bee’s scientific name but there is so much more we can know about each bee species. We need to know what size hole they prefer, what nesting materials they use, if they are specialists or generalists, and when they are active. The answers to these questions can be answered by anyone that takes the time to watch the bee guests and protect their nesting materials.