Ground Nesting Bees in the Garden

Earlier this year I wrote about planting for pollinators. In that post I briefly introduced various things that people can do to encourage pollinator activity in their yards and gardens. One thing that I mentioned was the importance of providing nesting sites. Most pollinators are insects and insects are small, so the distance that they are able to travel in search of food is relatively limited. According to the Xerces Society, the smallest bees can only fly a few hundred feet from their nests. Providing nesting sites in close proximity to foraging sites is incredibly important.

Roughly 70% of native bee species in North America are ground nesting bees, so chances are pretty good that if you are providing forage for bees in your yard, a good number of the bees that visit will be ground nesting bees. In order to ensure the survival of these bees, consider providing nesting habitat for them on your property.

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Lasioglossum leucozonium – a North American ground nesting bee (also known as a sweat bee) – photo credit: www.eol.org

Here are a few things to keep in mind when developing nesting habitat for ground nesting bees:

Create and Maintain Undisturbed Bare Ground: You may already have ground nesting bees living in your yard and you don’t even know it. Obvious evidence of nests is difficult to spot. If you can find tunnel entrances, they will look like small ant mounds. If you find a series of small “ant mounds”, watch for bee activity during sunny times of the day. Activity can be quite ephemeral though, so it is difficult to know if bees have just moved in or if they have moved on. Avoid tilling up soil and walking through areas where you suspect or intend for bee activity. Leave patches of bare ground unplanted and unmulched in order to encourage bees to nest there.

Sunny and South Facing: Bees are most active when the sun is shining and temperatures are warm. For this reason they tend to build their nests in warm, sunny spots. However, warm, sunny spots are also the best locations for many plants. Consider sharing these sites with ground nesting bees. Avoid putting down mulch in these areas and keep vegetation sparse and minimal.

Avoid Pesticides: When encouraging pollinator activity in your yard and garden, it is best to avoid using pesticides as much as possible. Herbicides kill potential food sources. Insecticides can kill pollinating insects along with pest insects. And soil fumigants can harm ground nesting bees.

Provide Some Accommodations: Due to the diversity of ground nesting bees, it is difficult to provide nesting habitat for all potential species. Some prefer loose, sandy soil while others prefer smooth, packed ground. Some bees will nest on level ground, while others prefer sloped ground. The habitat you are able to provide will depend on the conditions present on your property. Some modifications can be made, but this all depends on the resources available to you and how particular you want to get. Apart from maintaining a patch of undisturbed, unmulched, south facing ground, there are three additional things that you can offer ground nesting bees to make them feel more at home on your property: food (in the form of diverse flowers blooming throughout the growing season), a water source (in the form of a birdbath or something similar), and a few rocks for the bees to perch on and warm their tiny bodies.

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The tunnel entrance of a ground nesting bee.

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Tunnel entrances are often found in groups in areas of bare ground mixed with patchy vegetation.

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