Expert consulted: 
Not every bee lives in a hive and makes honey. But some of those other bees are necessary for a healthy garden.
Mason bees, for instance, are small native bees with 150 species found in North America. Unlike social bees, such as honey bees, they’re solitary.
“Mason bees build their nests in pre-existing cavities, such as holes in wood, hollow stems, or bee hotels,” says Michael Skvarla, PhD, entomologist and assistant research professor of arthropod identification, Penn State University. “They’re great pollinators, collecting pollen on the underside of their abdomens.”
Mason bees (family: Megachilidae) are about 3/8 to 5/8 inches long and are dull brown, black or metallic blue. They're named for their habit of building nests from mud in the holes they use to keep their eggs safe.
After mating, the female mason bee provisions each cell, holding 4 to 10 eggs, with pollen and nectar for the larvae to feed on once they emerge, says Skvarla.
The larvae then spin a cocoon and ride out the winter, snug in their nest. When spring arrives, the adults appear. “They’re some of the earliest spring fliers,” says Skvarla. Many types of mason bees hatch out in early to mid-spring, but other species hatch in mid to late summer.
Why Mason Bees Are Good to Have Around
Many types of mason bees are specialists: they pollinate specific plants, such as blueberries. Others are generalists and will pollinate many different plants, says Skvarla.
In fact, in some places, mason bees are used to pollinate commercial apple orchards and blueberry fields instead of honey bees, as their lifecycle more closely matches with the plants' pollination periods.
So, whether you grow flowers, herbs or vegetables, these little bees are great to have around!
Unfortunately, “like all pollinators, mason bees are threatened by habitat destruction,” says Becky Griffin, a pollinator health associate with the University of Georgia’s Great Southeast Pollinator Census. “When we take away a ‘messy’ field or clean up our yards around our home, [mason bees] have no place to nest and reproduce.”
How Do I Attract Mason Bees to My Garden?
If you’d like help support a healthy population of these vital pollinators, you can attract mason bees to your garden with these tips:
- Plant bee-friendly flowers, especially open, flat flowers such as daisies, asters, echinacea, or umbrel-shaped flowers such as ammi and daucus. Avoid planting only double-petaled flowers, which have been hybridized and often contain no pollen or nectar that bees need, says Skvarla. (Here are some more tips on how to grow a pollinator-friendly garden.)
- Leave some areas of your garden more wild, such as a section of your back yard. “It’s not good for them if your garden is too tidy because they have no place to nest,” says Griffin. Leave flower stems intact, or if you want to clean up, bundle stems up and stack them somewhere else in a protected area, such as under shrubs in your garden, for the bees to discover.
- Provide water. This is helpful if it’s very dry, especially during mid-summer. The bees will find it if you fill a bird bath with pebbles so they can land and sip the water, says Skvarla.
- Limit the use of pesticides. This benefits all the pollinators in your garden, not just mason bees, says Griffin.
- Put out a bee hotel. It’s best to get them out in early spring to offer nesting to a wider range of species, but you can put them out at anytime, says Skvarla.
How to Make a Bee Hotel
Providing a nesting habitat is a great way to invite these little bees to your garden, and it’s not difficult, says Griffin. The University of Georgia has step-by-step instructions on their site, but here’s basically what to do:
- Cut a piece of untreated wood to your desired size, and add a small roof to protect the nesting site from rain. Paint the outside, if you like, but not the nesting side.
- Drill about a dozen holes of various sizes from 5/16 to 3/8 in the block of wood. Because each species has a preference for the stem diameter they like, you should include various hole sizes, says Skvarla. The depth of the hole should be the length of the drill bit.
- Mount your box in a sheltered area that gets morning sun (but not in full shade or in a spot that is located in the blazing sun of mid-day. Place the box about 5 feet off the ground, and don’t worry if it’s not right next to your garden; the bees will find their way there, says Skvarla.
Most importantly, clean or replace your bee hotel every year. “Fungal pathogens and mites will build up, but the bees will still go there and be harmed,” says Skvarla.
If you’re not into DIY-ing, you also can purchase a bee hotel. Look for models that come apart for cleaning, rather than those that are glued together and cannot be sanitized. One type has slats of wood bolted together so that you can take it apart after the bees emerge in spring and scrub it clean, says Skvarla.
Do Mason Bees Cause Damage?
Because they only nest in existing holes, they do not cause damage to your property, says Griffin.
Worst case scenario? Skvarla says he once found they’d plugged up the exhaust in a string trimmer, which was simply a minor nuisance.
Do Mason Bees Sting?
Rarely! They’re not interested in what you’re doing in your yard and are mostly going about their own business. “Because they’re a solitary bee, they’d rather fly away and make a new nest than defend it,” says Skvarla.
But if you accidentally grab one (and squeeze), it may sting you, says Skvarla. However, this is not at all the same scenario as if you upset a nest of yellow jackets, which can sting repeatedly and will send alarm pheromones to alert everyone to come aggressively defend the nest. (Here's how to get rid of yellow jackets.)
Dr. Michael J. Skvarla, PhD, is an Assistant Research Professor of Arthropod Identification at Penn State Extension in University Park, PA, where he is the head of the Insect Identification Laboratory, which specializes in ID'ing insects submitted by the public.
Becky Griffin is a Community and School Garden Coordinator at the University of Georgia Extension and the project coordinator for the Great Southeast Pollinator Census which seeks to generate useful data about pollinators for researchers.
