What do Mason Bees Pollinate?

Do Mason Bees and Honey Bees Compete?

Reading Time: 5 minutes

Most Osmia mason bees are generalist pollinators, foraging on a wide variety of plants. As a rule of thumb, Osmia prefer tube-shaped blossoms or flowers with irregular shapes. Some of their favorites are various mints, penstemon, scorpionweed, and willows. They also like legume family plants such as indigo bush, clover, and vetch along with composites such as thistles.

But eclectic as most Osmia are, some of the species prefer specific plants or families of plants. Growers have taken advantage of this characteristic to enhance pollination of some our most important crops.

Mason bees live the irregular flowers of the mint family plants.

Osmia lignaria, the orchard mason bee, is a specialist on the Rosaceae family. What crops are in that family? For starters, we have apples, peaches, apricots, pears, plums, cherries, almonds, strawberries, blackberries, raspberries, and dozens more. In fact, the Rosaceae family is often listed as the sixth most economically important plant family.

Not only are the Rosaceae crops vital to our way of life, but they often flower too early for adequate pollination by honey bees. Honey bees would rather stay tucked in their hives on cold spring mornings, but the orchard mason bee has a family to raise and only six weeks to get it done.

In addition, some of these crops have flowers that yield only minor amounts of sugar. Some flowers, such as those of pear trees, are so low in sugar that honey bees don’t bother with them, even on a warm day. The reason is simple: honey bees need high-sugar nectar in order to make honey. Nectar with a low sugar content takes too long and requires too much energy to dehydrate, so honey bees would rather skip it entirely.

Other Osmia bees suitable for fruit tree pollination are the imported horn-faced bee (Osmia cornifrons) and the taurus mason bee (Osmia taurus). Both of these bees were imported by the USDA to assist with fruit tree pollination. In addition, the horn-faced bee currently pollinates over half the apple crop in Japan where it has been used for more than 50 years.

Another useful Osmia species is especially fond of plants in the heath family (Ericaceae). The so-called blueberry bee (Osmia ribifloris) is used to pollinate both blueberries and cranberries, especially in the western and southern states. These bees are a lovely shade of metallic blue, and can sometimes be seen in the wild foraging on Manzanita and other Arctostaphylos species.

Also found in the west is the small, brilliant green Osmia aglaia that is raised commercially to pollinate raspberries and blackberries. They begin to emerge just as the orchard mason bees are completing their season and the wild blackberries are beginning to bloom.

Osmia aglaia, sometimes called the raspberry bee, is used for commercial pollination of raspberries and blackberries in the west. They are very small and brilliantly green.

What Makes Mason Bees Good Pollinators?

You will often hear people say that mason bees are better pollinators than honey bees. What does this mean?

A number of things set mason bees apart from honey bees. The first, as I mentioned above, is that honey bees are not interested in low-sugar nectar. Mason bees, on the other hand, use very little nectar. When they get tired or thirsty, they simply slurp some nectar from the closest flower, regardless of the sugar content. They also use a little nectar to moisten the pollen as they prepare a mound to receive an egg. It only takes a drop here and there, while a honey bee colony uses gallons.

A second difference is the ability of mason bees to fly and work in colder weather. The mason bee life cycle allows them to start work sooner in the spring and earlier in the day, often working while the honey bees are still holed up inside their hives.

In third place is speed. Mason bees work faster, darting from flower to flower at a much quicker rate than honey bees. Although honey bees can fly very fast in a straight line, when they are working flowers, they tend to dork around and take their time. Try taking pictures of both, and you can feel (and see) the difference.

Lastly, the pollen on a mason bee’s body is held loosely. They have hairs for collecting pollen on their abdomen (called a scopa), and also on their face. They use their legs to push pollen into the scopa where individual pollen grains can easily rub off onto the next flower, allowing pollination. Honey bees, on the other hand, have a pollen press on each hind leg. The honey bees moisten the pollen with nectar and then press it into the pollen baskets on each leg. This pollen — wetted and pressed — is like dough. It is unusable for pollination because it won’t rub off onto the next flower.

Taken together, it is easy to see why a few mason bees can do more work than an entire colony of honey bees. In fact, the USDA estimates that 300 mason bees in an apple orchard can perform the same pollination as 90,000 honey bees (two large colonies).

Do Mason Bees and Honey Bees Compete?

Certainly, any two species that live in the same environment and use the same resources compete with each other. After all, there is only a finite amount of pollen, nectar, and habitat to go around. But how much bees compete with each other is a complex question.

Studies have shown low amounts of competition between managed and native bees in some cases, and high amounts in others. Results vary depending on the environment (agricultural, suburban, urban), geographic area (deserts, prairie, rainforests), seasons, and the types of bees that live there naturally vs the type being managed. Then, too, studies by environmentalists often show different results than studies done by schools of agriculture. For one interesting perspective, read NPR’s short essay, “Honeybees Help Farmers, But They Don’t Help the Environment.”

For me, the answer lies in moderation. By limiting the number of honey bee colonies we maintain, and providing resources that all bees can use, such as flowers, water, and habitat areas, we can help all bees to thrive. In addition, I believe beekeepers have a responsibility to maintain healthy, disease-free colonies that are unlikely to infect wild bees with the pathogens and parasites that have so harmed our honey bees.

In addition, I believe beekeepers have a responsibility to maintain healthy, disease-free colonies that are unlikely to infect wild bees with the pathogens and parasites that have so harmed our honey bees.

Gardeners often have great ideas for helping their pollinators. What have you done to help yours?

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