Attracting and Keeping Solitary Bees as Pollinators
Solitary bees unlike the common honeybee do not create large colonies of individuals and store honey for food. Each female lays an egg on its nectar and pollen food source and leaves the egg to develop on its own.
In the home vegetable garden you will more often see the solitary bees acting as pollinators on the vegetable flowers.
While most of the solitary bees nest in the ground and so we can not make artificial nesting places to attract them there are two main types that nest in hollow tubes and so can be managed as pollinators for the home garden.
Megachilidae: This family of bees includes mason bees and leaf-cutter bees. These bees nest in tubes.
There are 140 species of Osmia in North America.
Blue Orchard Bee Osmia lignaria Leaf Cutter Bee Megachile
Hylaeus and Ceratina are solitary bees which nest in pithy stems of plants or holes the eat into rotten wood
The solitary bees typically have a 300 to 600 foot foraging radius from where they were born as compared to the honey bee that can forage over a 2 to 4 mile distance from the hive.
They are generalist foragers, meaning they gather nectar and pollen from many types of flowers.
Solitary bees are ectothermic, meaning their bodies do not regulate and retain heat. They need a body temperature above 90°F in order to fly. As such they warm their bodies in the sun, and by vigorously vibrating their flight muscles to get their bodies up to flight temperature. This is why when placing the nest you want them exposed to the early morning sun to aid in their warming of their body temperature in the morning.
When preparing a nest site, the female bee will place a dab of mud at the end of the nest. The bee then begins to place up to twenty-thirty loads of nectar and pollen at the end of the tube. Once sufficient food has been collected, an egg is laid and she then seals that segment of the nest with a thin mud plug. This process is repeated for the length of the hole until she places an extra thick mud plug at the end to prevent pests from entering her nesting eggs.
Mason bees require mud with a heavy clay texture to build their nests in holes in wood, and other hollow tube cavities and are sensitive to the moisture level of the mud. So this is one of the few times when it is beneficial to have that heavy clay soil in your garden. While the bees will forage for the mud used in their nest construction you can help them out by creating a “mud puddle” to use as the source for their building material. This also serves to attract and keep the bees in the area since if there is not a good source of mud they will move to an area where it can be found.
Leafcutter bees require leaves or flower material to cut and bring back to the nest. They seem to prefer pea plants, roses, lilacs, and dahlias. You can tell you have them in your garden by looking for their distinctive circular cutting of the leaves on the plants.
The mason bee’s pollination season is approximately two or three months beginning at the time the fruit trees bloom in the spring. As a result, many of the plants that blossom later in the season won’t benefit from the pollination of the mason bee.
Leafcutter bees may have multiple brood cycles thru the season and can provide pollination nearly the whole growing season.