Habitat Feature: Bare Earth for Native Pollinators

Photo © Greg Habermann

There are over 4,000 native bee species in North America, and unlike the familiar honey bee (Apis mellifera), many of these native bees nest underground. Keep a part of your yard as bare ground to provide nesting habitat for native bees. Below we discuss some of our more common native ground-nesters, and some ways to support them.

Digger Bee

Photo © NY State IPM Program at Cornell University

Common early spring nesters include cellophane bees (Colletes spp.), mining bees (Andrena spp.), and small sweat bees (Lasioglossum spp.). These bees all gravitate towards sandy, well-drained soils on south facing slopes. The warmth from sunlight on south facing slopes helps to heat up their cavities on cold, spring mornings. And, in general, south facing slopes tend to be drier. Areas that are frequently wet compact the soil and don’t allow for easy tunnel building.

Mining Bee Nest

Photo © Sarah

Only females build tunnels for nesting. Most will build solitary nests, but frequently several females will construct tunnels in the same vicinity. Some, like sweat bees, have separate nesting chambers but are interconnected through tunnels underground.

Mining bee with pollen

Photo © Nigel Jones

At the end of the tunnels females make a chamber in which they lay an egg and provide pollen and nectar rations to support the developing larva after it hatches. Fascinating research of solitary bee species in Europe found that some species of bee had to visit over 2000 flowers in order to gather enough pollen to feed one larva. Most flowers have evolved to keep a bee from harvesting all the available pollen (this increases their chances at having that pollen successfully reach more flowers to complete the fertilization process), driving up the number of flowers it is necessary for a bee to visit to collect enough pollen. Decreasing solitary bee populations may be linked to declining food supplies for these bees as there is less habitat available for flowers.

Native bee on flower

Photo © Bob Peterson

In your yard you can help native bees by leaving south facing slopes, with well-drained and sandy soils, partially bare. Or, at least refrain from using mulch on all exposed patches of your garden. If you see little “volcanos” of soil accumulate with a central hole, you may have attracted nesting native bees. These bees are relatively gentle, compared to honey bees. However, they have the capacity to sting and get aggressive if you come too close to their nesting cavities. To avoid issues, stay clear of their chambers once they’ve started laying eggs.

Bare earth in Garden

Photo © Simon Roberts

Native bees take about three to four weeks to build nests and lay eggs. After that time, they will abandoned the chambers, and go about their pollinating lives while their larvae mature into adults. Once the offspring emerge, either later in the season, or the following spring, a new generation of pollinators will busily explore your gardens providing the invaluable service of pollination. Not a bad deal for a little exposed earth.

Cellophane bee (Colletes inaequalis) Emerging

Photo © Rob Cruickshank

Adding a patch of bare earth to your Map is easy. Just use the “ground” habitat (). This can be found under “Tool Shed” –> “Habitats” –> “Ground.” Be sure and set the characteristics to describe your patch of bare ground, and leave a note about your bare ground to help spread the word about this important habitat feature with other Habitat Network participants.

Get naked in your yard for bees! Bare earth supports native pollinators.

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Do you live in IL, IN, IA, ME, MA, MN, OH, VA, WI or Ontario, Canada? If so, consider the role you can play in helping to create habitat for the endangered Rusty Patched Bumble Bee (Bombus affinis). The USFWS can help.