Keeping solitary bees
Bees make up the largest portion of pollinator species in North America and are important to the pollination of food crops as well as flowers.
When most people hear about keeping bees, they think of beehives full of honeybees. However, there is another kind of bee you can keep at your home: solitary bees. Solitary bees are bees that live independently and do not make honey.
Of the roughly 4,000 species of bees in North America, more than 90% lead solitary rather than social lives. Solitary bees have individual nests but will make their nests adjacent to other individual nests. The most common solitary bees are mason bees (Osmia spp.) and leafcutter bees (Megachile spp.), and are important pollinators found across the nation. Both species are named for the nesting material they use: mason bees use mud to create their nests, while leafcutter bees cut out portions of plant leaves.
Mason and leafcutter bees are both tunnel-nesting bees, which means they need a tunnel to make their nest. Once the bees find a suitable cavity, they use their nesting material to create brood cells within the cavity. Each brood cell contains a mass of pollen and some nectar onto which a bee lays one egg. They then seal the cell using more nesting material.
During the summer, the eggs hatch and the larvae eat the pollen in their cell until pupating and then overwinter in the cell as an adult bee. In the spring, the bees hatch out and the process begins again.
Providing these solitary bees with a home full of nesting tubes is an excellent way to support these pollinators. This method can be used effectively in urban and rural settings. Solitary bee houses, also known as bee hotels, bee condos, or bee nest boxes, can be purchased commercially. You also can make your own bee house with supplies purchased at garden centers or online.
To build a solitary bee house, first find a structure to hold the nesting tubes. This structure should keep the tubes secure while also protecting them from wind and rain. Bee houses can be made from untreated wood, cinder blocks or cut PVC pipe. The house should have a back for one end of the tube to rest against so only one end of the tube is open, as solitary bees will not nest in an open-ended tube.
Be sure to include a roof that hangs over the opening to protect from rain or place the bee house in an area that is already covered.
After making the bee house, add the nesting tubes, which is where your solitary bees will create their brood cells. The tubes should be removable and made from a breathable material such as hollow plant stems, bamboo or cardboard tubes.
Nesting tubes should be 5 to 6 inches long and anywhere from 1/4 to 3/8 inch in diameter for mason bees and 1/8 to 1/4 inch in diameter for leafcutter bees. Providing a range of tube sizes in your nesting house will attract both solitary bee species.
Place your nesting tubes inside the bee house with one open end against the back of the house.
An alternative to this type of bee house is a house with tunnels drilled into a block of wood. To create this type of bee house, use at least an 8-inch-long block of untreated wood 4 inches by 8 inches. Use a drill to create holes in the wood for the nesting tunnels. Be sure to not drill the entire way through the block of wood. The length and dimension of drilled holes should be in the same range, length and dimension as the nesting tubes.
Bee wings are delicate; protect them by drilling perpendicular to the wood grain, using a sharp bit at a high speed, and sanding smooth the openings of the holes.
Ideally, bee houses should be placed 5 to 6 feet above the ground and facing southeast or east to capture the morning sun. Make sure nothing is blocking the entrance to the house, including any tall flowers or other vegetation. The house should be mounted securely to a post, building, isolated tree or other sturdy structure. It is vital to place your bee house in a location that is protected from any drifting pesticide spray.
There is nothing you must do to attract mason and leafcutter bees to your bee house, they will find the house on their own. However, a pollinator-friendly garden will attract them to the area. Mason bees are active in early spring while leafcutter bees are active during the summer, so it is important to plant flowers that will bloom at various times throughout the season.
Early spring blooming plants include serviceberry (Amelanchier canadensis), red columbine (Aquilegia canadensis) and dandelion (Taraxacum officinale). Dandelions are considered a weed by most; however, for the urban and suburban solitary beekeeper who may not have the space to plant large, spring blooming shrubs or trees, they are a readily available source of pollen and nectar. Pollinator plants that bloom throughout the summer include purple coneflower (Echinacea purpurea) and zinnias (Zinnia elegans) while black-eyed Susan (Rudbeckia hirta) and milkweeds (Asclepias spp.) bloom from late summer into the fall.
Inspect your bee house throughout the summer and autumn months as they are susceptible to pests, disease and predators. It is important to keep your house clean to minimize the risk of pests and disease.
Used nesting tubes should be replaced each year after the bees emerge. If your box has nesting tubes that cannot be removed, the nest should be replaced each year.
You will know that a nesting tube has been filled with brood cells when the end of the tube has been capped off with nesting material. Once all of the tubes are filled or the cooler temperatures of fall have set in, the tubes can be removed from the house and placed in a cool, dry place such as an unheated garage or shed. The tubes can be stored in a mesh bag to protect from parasites while in storage. If your bee house is one with holes drilled into it, the entire house can be stored in the same manner as individual tubes.
In early spring, you can place the filled tubes in the nesting box along with fresh nesting tubes. The adult bees will create a hole in the cap of the filled tube and emerge. Once a tube is completely empty it can be discarded.
An emergence box also can be used to ensure bees do not try to nest again in their original tube or drilled hole. An emergence box can be made from a plastic bin with a 1/2 inch in diameter exit hole cut into one side. The filled tubes or block of wood can be placed into the bin and, with the lid closed, the exit hole will be used by the emerging bees. Place the bin next to the house with the new nesting tubes and the emerging bees will use the newly refreshed bee house tubes.
Keeping solitary bees is an activity that can be enjoyed with your family to promote pollinators.
Penn State Extension has additional information about solitary bees (https://extension.psu.edu/programs/master-gardener/counties/clinton/news/solitary-bees; https://extension.psu.edu/spring-bees-who-are-they-and-where-do-they-live). To learn more about keeping solitary bees, call the Master Gardeners of Butler County Garden Hotline at 724-287-4761, ext. 7, or email butlermg@psu.edu.
Amy Cirelli is a Penn State Extension Butler County Master Gardener.
