Backyard Gardening

By Charles Kincaid and James Randall

Often, when we hear the word “bee”, many of us think of a highly social insect, like the honeybee that lives in hives containing several thousand members of its species.  That concept of bees is incomplete.  Of roughly 4,000 species of bees in North America, more than 90 percent lead solitary rather than social lives. Bees make up the largest portion of pollinator species in North America and are important to the pollination of food crops as well as flowers.

What are Solitary Bees?

As the name implies, solitary bees live alone, procure pollen and nectar, and create nests for the next generation of their species.  Male solitary bees help to create the next generation, but are not responsible for caring for their offspring.  Each female solitary bee constructs her own individual nest tubes, and provisions her own nest without any help from other members of her species.  

Solitary bees live for approximately one year, but we only see them during their active stage which lasts for 2-4 weeks in early spring, mid-summer, or early fall. Most solitary bees make their nests in the ground and appear in the early spring.  Each bee nest cavity has several separate brood cells in which the female lays one egg.  The female mixes together pollen and nectar to form a loaf of bee bread inside of each egg cell.  Solitary bees may be floral generalists that will gather pollen from many kinds of flowering plants or be host plant specific, which means they are limited to feeding on just a few or even just one species of plant.  

Solitary bees use nesting sites that provide protection from the elements and from predators.  About 30% of solitary bees nest in cavities in hollow stems and pre-existing holes in wood such as branches or tree trunks.  The remainder, approximately 70% of solitary bees, nest in the ground.  They excavate nests in bare soil or sparsely vegetated areas under plants.  They prefer sandy, loose, and well drained soils.

Solitary bees range in size from 0.5-0.75 inches, and may be a variety of colors such as blue, green, copper or metallic red.

How do they impact the environment?

Bees are important pollinators of food crops. They play a role in pollinating a variety of the fruits and vegetables we eat, from apples, to blueberries, to pumpkins and zucchini.  Our diets would be limited without them.  Insects in general are in decline in the U.S. and that includes solitary bees.  We can help them thrive in our local environment by making some relatively simple accommodations.  

According to Michigan State University, solitary bees are not a stinging hazard to humans (https://www.canr.msu.edu/news/solitary_bees_in_yards).  In comparison to social insects like yellowjackets and social honeybees, who do defend their nests and can be territory aggressive, solitary bees are relatively harmless. There is generally little need to control them.  

Damage to lawns and turf is usually minimal and control may be sought because the bees are perceived as a danger or annoyance. Outdoor activities, including lawn mowing, can often be continued with no problem. However, with very large aggregations, you may prefer to avoid the area for four to six weeks while solitary bee nesting is taking place.

How can you support solitary bees in your landscape?

There is a recognized decline in the populations of pollinator bees, including solitary native bees, in North America.  The decline results from a combination of loss of habitat, increased use of pesticides, and landscaping practices.

The easiest way to support solitary bees is to leave your landscape a little messy.  Don’t cut back pithy stems to the ground.  Leave some leaf litter.  Stack fallen twigs and wood into small piles of branches, twigs, and rotting logs.  Instead of removing all the dead debris, create small piles throughout the garden that are attractive to many of the solitary bees.  To promote nesting of cavity dwelling solitary bees leave standing deadwood or provide bee nesting boxes.  Logs can be used as borders around a native planting area and will provide potential nesting sites. 

Native perennials have hollow or pith-filled plant stems.  Cavity nesting solitary bees, such as carpenter and mason bees, can nest in the hollow stem or preexisting cavity to lay eggs.  Allowing these stems to remain in your yard or garden will provide nesting sites for solitary bees.  The Xerces Society has a tip sheet, Save the Stems: How to Create Habitat for Stem Nesting Bees at https://xerces.org/publications/brochures/save-the-stems to guide you.  Dead trees or logs laying on the ground can also provide habitat.  Porous rocks with cavities like limestone are sometimes utilized as nesting sites.  

The burrows of ground nesting solitary bees look like ant hills with a raised entrance.  Provide areas of bare soil and protect existing nests from disturbance like tilling or compaction.  To encourage ground nesting bees, leave existing nesting sites, areas of bare soil and rodent holes in the landscape.  Avoid heavy layers of mulch or landscape fabric, which can restrict access to new nesting sites.  Provide undisturbed nesting sites like patches of soil insulated with fallen leaves.  Resist the urge to neaten up your yard. Leave it messy until May and the bees will thank you.

Go native- Add more native plants to your garden. Pollinators native to our region are adapted to feed on native plants. They have evolved together. There are many beautiful native plants that can be added to garden beds.  Penn State Extension Master Gardeners can help you choose natives that will enhance your landscape and provide food and habitat.  A diverse garden with many plants is more bee-friendly.

Go Pesticide Free- A bee-friendly garden eliminates or dramatically reduces the use of all pesticides, including insecticides, herbicides and fungicides. While these products can sometimes be useful in controlling harmful pest, they can be detrimental to our pollinator bees.  Learn more about integrated pest management approaches to controlling pests that do not rely on pesticides.

Add a Pollinator Bee Box-Just as we retreat to our homes to endure winter, cavity dwelling solitary bees can benefit from bee houses to help them survive the elements. Bee houses do not have to be fancy. They can be made from untreated lumber or a log. Simply drill various size holes ranging from an eighth to a quarter inch in size in the wood. The holes should be several inches or more deep for best results. Hang on a fence or post in a sunny location and soon the native bees will come. Other box ideas include paper drinking straws layered in a tin can or even hollow perennial debris tied together and hung from a tree.  Boxes are available commercially and can be built by do-it-yourself hobbyists.  

Solitary bee activity can be spotted in the nesting box as the holes will become plugged with a mud-grass-like mixture. The bees will lay eggs in the holes, covering and protecting them from invaders and the elements with the mixture.  Remember, you can also just leave debris in the garden to create habitat.

Solitary bees are the pollinator workhorses of our environment. Welcome them to your garden and landscape. It is so easy to make them feel at home.

Charles Kincaid and Jim Randall have been certified Master Gardeners in Clinton County since 2019.  They can be reached at Clintonmg@psu.edu or through the Master Gardener hotline at (570) 858-0198