A few days ago, our blog post was about the wonderful idea that you can teach your kids and grandkids about bees and pollination by renting mason bees in their bee house for your backyard garden.

Soon afterwards, we became aware that mason bees are in decline in half a dozen US states, so we thought we’d tell you this too in case you are “on the fence” about helping the mason bees out.

For 13 years, volunteers across the mid-Atlantic region helped scientists track mason bees. Backyard data in 6 US states shows that mason bees are declining.

People everywhere are starting to realize that bees face serious survival issues from habitat loss to pesticides. Save the Bees can be seen all over the place, but there is less talk about the underlying issue, which is, why do bees need saving?

A recent study published in Scientific Reports tracked mason bee populations to see why they are struggling. The study used data collected in Delaware, Maryland, Virginia, West Virginia, and Washington, DC over the span of 13 years.

This unrelated 2:22-minute video by Oregon Metro gives us tips on raising mason bees:



The study was conducted by Kathryn LeCroy, a PhD student at University of Virginia, and her colleagues. They found that year after year, six species of native mason bees in the genus Osmia have a steady decrease in their populations.

In stark contrast, two related species that came to North America from Asia in the twentieth century are thriving. Scientists studied the horn-faced bee, a fruit crop pollinator brought to the USA that had a steady population count. Osmia taurus, a non-native species that came to the USA accidentally, had a population increase of 17% every year of the study, with an 800% increase in total.

No indication was found as to why native species are declining. LeCroy believes the exotic non-native bees may be at least partly responsible for the downfall of the native bees, since they are all competing for the same resources. Unusual diseases could also be in play.

Native pollinators are well suited to commercial pollination, but farmers usually seek European honeybees. According to LeCroy, mason bees are master tree crop pollinators, like almond trees, and their presence can make honeybees even more efficient at pollinating. Mason bees are also major pollinators of our natural ecosystems, for early blooming spring trees like eastern redbud.

Mason bees are solitary, they are not social bees like the honeybee. Female mason bees build partitions in holes between rocks, in trees, anywhere they can compartmentalize solo rooms for each of their eggs.

LeCroy and her colleagues compared three sets of data, as recent as 2017, from a wide range of research groups and volunteers over many years and applied other pertinent criteria as well. Volunteers did pan trapping in their back yards, capturing live bees from their neighborhoods and freezing them until LeCroy could return to pick up the samples. She then cleaned, identified, and recorded them.

In addition to identifying the bees on their property, LeCroy learned from them what is important about the land where they live. In one rural part of Virginia, a mason bee had not been recorded in the county since 1924. She found this the most fulfilling scientific experiment she had ever had.

Not much has been discovered yet about why mason bees are in decline, but hopefully over time it will become more obvious so we can do something to stop it in its tracks.

Meanwhile, how can everyday people help Save The Bees? According to LeCroy, there are many things we can do. Participate in scientific studies like this one as citizen scientists, support your local pollinator community, advocate for planting pollinator-friendly native plants wherever possible… at home in your garden is easiest, but also at schools, parks and other public spaces like roadsides and medians.

And that brings us back to where we began. How about renting a mason bee house for your garden this summer? Check out our previous blog post for more details so you too can have a delightful experience with bees while you Save The Bees.