June 21 to 27, 2021, is Pollinator Week, an annual event to support pollinator health. The super-pollinators of the garden are … native bees! While honey bees have their place, it’s our native solitary bees—such as mason bees and leafcutter bees—which are critical to growing food and flowers. Learn more about these amazing heroes of pollination—and see how to bring these docile bees to your garden.
Solitary Bees: The Heroes of Pollination
Most of us grew up learning about the sophisticated social structures of honey bees and bumblebees, and we’ve come to think that their lifestyle represents all bee behavior. The truth is, the world is home to more than 20,000 species of bees, and a whopping 90% of them do not live together in hives.
Instead, most of the world’s bees are solitary, meaning they live alone. Unlike social bees, each female solitary bee has to gather pollen and nectar, build nests, and lay eggs all on her own, without the help of hundreds or thousands of doting workers. And although honey bees tend to get all the credit for keeping our crops going, native solitary bees are almost two to three times more effective pollinators!
So, if 90% of bees don’t live in hives, where do they live? Well, about 70% of solitary bee species nest underground in tunnels and burrows, while the remaining 30% nest aboveground, in holes in logs and stems.
Mason bee nesting holes capped with a layer of mud and clay. Photo by Dominicus Johannes Bergsma/Wikimedia Commons.
Two of the most common hole-nesting bee species used for crop pollination are alfalfa leafcutter bees and blue mason bees. In the wild, both species nest in pre-made holes, such as old grub tunnels, crevices in peeling bark, or broken branches. As suggested by their names, leafcutter bees use pieces of leaves to build their nests, while mason bees use mud or clay. Other types of hole-nesting bees, such as sweat bees and carpenter bees, prefer to excavate their own holes in the ground, logs, reeds, or the dead canes of raspberry bushes.
A curious carpenter bee (Xylocopa spp.)
Most solitary bees have a short lifespan as flying adults. Male mason bees only fly for about two weeks—just long enough to mate—and females only live a few weeks longer. With such a short adult lifespan, solitary bees have to use their time wisely! They do not have time to make honey, nor do they like to fly too far from home, meaning they spend the bulk of their time preparing their nests and pollinating flowers within a relatively small area. A big chunk of a solitary bee’s life is spent in their mother’s nesting site, hibernating over winter in their cocoons.
Mason bee (Osmia spp.).
Backyard Bee Houses
Some reports indicate that nearly 40% of bees are facing extinction today, leaving many people wondering what they can do to help. Fortunately, the best thing you can do is to start local, in your own backyard. Making your garden as bee-friendly as possible is as easy as adding things like native wildflowers and native bee nesting sites, including bee houses.
Similar to birdhouses, bee houses (or hotels) provide vital and otherwise missing nesting habitat. They are relatively simple in form, consisting of a birdhouse-like structure containing a series of exposed, reed-like tubes that the bees can lay their eggs in. Hole-nesting bees desperately search for appropriate nesting sites, sometimes even nesting in the ends of old garden hose nozzles, openings in metal garden furniture, or the hollow ends of wind chimes. Bee houses provide a more natural structure for the bees, and also allow for a bit of human assistance when necessary.
Bee houses can be an eye-catching addition to your garden.
On an annual basis, bee houses do need to be maintained and managed, or else they’ll become uninhabitable. Don’t worry—maintaining a bee house is pretty simple: Just remove the bee-cocoon–filled nesting materials and store them in a cool place over winter. Then, in the spring, remove the cocoons from the old materials and place them alongside new materials in your bee house. The new bee generation will emerge and get right to work. In exchange for pollinating all of our fruits and vegetables, a little housecleaning and maintenance is the least we can do!
For more advice on maintaining a bee house in your garden, see How to Maintain a Bee House to Increase Pollination.
Solitary Bee Pests and Diseases
Like any other animal, hole-nesting bees are susceptible to a number of pests, diseases, and predators. The three greatest threats that the bees face are pollen mites (they eat the bee larva’s food supply before the bee can), 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).
To reduce the spread of pests and diseases in bee houses, simply harvest cocoons and separate healthy ones from infected nesting chambers. As you harvest cocoons, you’ll learn how to identify infected chambers and keep healthy cocoons safe.
For more information on native bees and bee houses, see our top tips for maintaining a backyard bee house.
To learn about keeping honey bees, see our Beekeeping 101 series.