When you hear the word "bee" you likely think of honey bees, right? Hives, honey, swarms, pollination, Winnie the Pooh, etc:
I'm hoping that based on previous posts, you also now think about bumble bees-- those big, colorful, fluffy bees flying nosily around all summer. They are probably my favorite. :-)
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| Bumble bee in Wisconsin. Photo credit: Carol Dolan |
But what about mason bees? Have you ever heard of them? Look at how beautiful they are! There are around 500 of these bees (in the genus
Osmia) found worldwide. Around 130 have been identified in North America. All of them have stout, roundish, bodies and almost all of them have a metallic sheen to them. Some are black, but many come in shades of blue, green, copper, and purple. You likely don't notice them as easily as you notice bumble bees or honey bees because of their size- the largest
Osmia is just over half an inch long.
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| Osmia sp. from Montana. |
Osmia is a genus in the family Megachilidae. In this family, females carry pollen on the underside of the abdomen, where bristly hairs (called scopa) are found. Unlike honey bees and bumble bees (but similar to the majority of North American native bees),
Osmia are solitary. This means they do not live in colonies. Each female works alone to provision a nest for her offspring. The female lives for just one season: she emerges as an adult in the spring, mates, provisions a nest for her offspring, and dies before the winter. New bees go through the entire life cycle in one summer. They metamorphosize from larvae into adults before winter, but stay within the cocoon until spring in a state known as diapause (kind of like hibernation).
Most
Osmia don't create their own nests, but use spaces that already exist in nature. Typically, the spaces that are chosen are long, narrow enclosures. Tunnels created by beetle larvae, hollow stems, and holes in tree trunks are the type of places
Osmia species choose for nests. The way they use these spaces is what's so fascinating about these bees. The queen will begin at the back of the nest and work her way towards the outside. Each egg is provisioned with a mixture of pollen and nectar. It has to be enough to feed the larva throughout the summer and to build up fat stores to survive winter. This is a lot of pollen and nectar- some studies of some species have shown that it takes 15-35 foraging trips and visits to around 75 different flowers to collect enough for just one egg!
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Osmia nest tubes: yellow is the mixture of pollen &
nectar; the brown is mud; each cell contains one egg.
You can see the queen in the tunnel on the right. |
After an egg is laid and enough pollen and nectar has been collected, the queen will seal that egg into a little cell created out of mud. (This is where the common name, "mason bee" comes from.) She collects the mud with her mandibles (jaws) and carries it between her jaws and front legs. Once a little wall of mud has been built to protect the first egg, she'll start collecting nectar and pollen for the next one.
The larvae will emerge and feed on the pollen/nectar throughout the summer. They will then pupate and go through metamorphosis to become adults. It is in this adult stage (still within the cocoon) that they will overwinter. The cells furthest back in the tunnel will be female, cells closest to the opening of the tunnel will be male.
In spring, the males will emerge first. They'll chew through the cocoon and the mud walls and then crawl out of the tunnel. Males tend to stay very close to nest openings once they emerge in order to mate with a female as soon as one comes out. Once mating occurs, the new females will each search for a new nest site.
A queen will use sight and smell to find her way back to her nest opening. It is not unusual for one bee to have more than one nest each summer, especially since nests are pre-existing burrows of a variety of shapes and sizes.
So why are
Osmia important? Well, they're really important native pollinators. Unlike honey bees which are not native to North America (they were brought over from Europe), there are hundreds of native
Osmia in the U.S. Native bees are often more efficient at pollinating native plants. One particular species,
Osmia lignaria (the blue orchard bee) which is used commercially to pollinate apples, almonds, plums, and cherries, is incredibly more efficient than honey bees. Research has shown that 300
O. lignaria can do the same pollination work as 90,000 honey bees!
Most
Osmia are generalists, so they will appreciate any flowers that you plant in your garden. However, they do seem to prefer the long, narrow flowers of plants like beardtongues (genus
Penstemon), mints (family Lamiaceae
), and the pea family (Fabaceae). Some species are specialists and focus on just one genus or species.
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Nest tubes that my friend Casey made
for her garden. |
You can easily create habitat for
Osmia species in your yard. Nests can be built out of a variety of materials. Hollow wooden tubes work well, holes can be drilled into larger pieces of wood, or you can remove the pith from large, thick plant stems and use those.
Once
Osmia start building nests in your yard, you'll be able to see a high level of activity in/out of the nest boxes, on your flowers, and in the dirt/mud. They're really fun to watch! (Try peering into the tubes with a flashlight in the dark to see sleeping bee faces!)
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Casey used wooden tubes and old cans. The
wooden "shelves" above the tubes are to
protect the bees and their nests from rain. |
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Casey made more nesting tubes by drilling into
wooden blocks and inserting plastic tubes into the
holes (so they can be cleaned and reused). |
Some of the stats were taken from
The bees in Your Backyard by Joseph S. Wilson and Olivia Messinger Carril (2016).
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“Bees do have a smell, you know, and if they don't they should, for their feet are dusted with spices from a million flowers.”
― Ray Bradbury, Dandelion Wine
