Ground Bees in Minnesota: A Common Yet Misunderstood Native Pollinator

Ground bees are a frequent sight in backyards and gardens across Minnesota from early spring through fall. While they occasionally stir up some alarm when homeowners spot them flying low and burrowing in lawns, these native bees are harmless pollinators that play an important role in our ecosystem. By learning more about these misunderstood insects, we can appreciate the value they bring and coexist safely with them.

What Are Ground Bees?

The term “ground bee” does not refer to one specific species, but rather a group of bees in the Andrenidae family that construct nests underground. There are over 20 genera and 130 species from this family documented in Minnesota so far. The most common ground bees belong to the mining bee genus Andrena.

Mining bees are medium-sized, shiny black bees covered in pale hairs. Females have more extensive hair tufts on their back legs for collecting pollen. Their furry thorax and sometimes abdomen give mining bees a fuzzy, teddy bear-like appearance as they visit flowers. Named for their burrowing habits, these bees excavate narrow tunnels in lawns, fields, or bare soil.

While Andrenids are the most familiar ground bees, others include sweat bees (Halictidae), which nest in colonies underground and carpenter bees (Xylocopinae) which burrow into wood. All ground-nesting bees lead solitary lives, with each female building and provisioning her own nest.

The Benefits of Ground Bees

Though ground bees don’t produce honey like honey bees, they are extremely valuable native pollinators. Various mining bees specialize in pollinating fruit trees, berry bushes, spring wildflowers, and more. Their early spring emergence coincides with blossoming trees and shrubs.

As generalist pollinators, mining bees visit numerous plant species. Females actively gather huge amounts of pollen to feed their offspring. A single mining bee can pollinate thousands of flowers each day as they busily move from bloom to bloom. Without these wild pollinators our gardens and agricultural crops would suffer.

Ground bees are also an important food source for birds, spiders and other insects. Their nests loosen and aerate soil while creating tunnels that small mammals later use for shelter. Overall these bees contribute to biodiversity and healthy ecosystems in Minnesota.

The Nesting Habits of Ground Bees

Female mining bees spend the majority of their lives underground tending to nests. They use strong mandibles to excavate narrow tunnels reaching up to 24 inches deep in the soil. Off these main burrows are small chambers where the bees construct brood cells for their eggs.

These solitary bees line brood cells with a liquid secretion that hardens into a protective waterproof coating. The female gathers pollen and nectar into a ball, lays an egg atop it, and seals off the chamber. She repeats this process, creating several individual brood cells in sequence along each tunnel.

The egg hatches within a few days and the larva feeds on its pollen provisions as it develops. It spins a silken cocoon and transforms into a pupa before emerging as an adult bee about a month later. The new bees overwinter underground before digging their way out in early spring.

Signs of Ground Bee Activity

Watch for these common signs of ground bees on your property:

• Conical mounds of excavated soil at nest entrances. Mining bees clear debris from their tunnels and push it outside, forming small piles around each hole.

• Multiple holes in lawns, gardens, or accumulations of bare soil. Ground bees rarely nest alone! Expect to see dozens of bees coming and going.

• Females hovering and diving to investigate potential nest sites in spring. They land briefly and dig test holes to check the suitability of the soil.

• Increased pollinator activity as ground bees forage low to the ground, moving rapidly between flowers. Watch for their frequent visits to fruit trees, berry canes, clovers, violets, dandelions, and more.

• Abandoned nest holes by late summer as most ground bees die off. Solitary bees have just a 4-6 week adult lifespan on average.

Dealing With Ground Bees in Your Yard

It’s understandable to feel concerned seeing ground bees actively tunneling in your lawn. Keep in mind they are non-aggressive insects that rarely sting unless grabbed or stepped on. Their presence indicates you have inviting habitat in your landscape. Here are some tips to reduce conflict:

• Move cautiously and avoid walking barefoot on lawns with ground bee activity. Give them space as you garden or mow.

• Never pour insecticides down active nest holes. This is illegal and may provoke attacks. Many insecticides are also harmful to beneficial pollinators.

• Landscape with native flowering plants that offer alternative pollen and nectar sources. This draws bees away from high-traffic areas.

• Maintain sections of your yard with exposed soil for nesting. Protect these areas from digging or trampling to avoid provoking defensive behaviors.

• Wait it out! Ground bee numbers naturally decline in mid to late summer as nests are vacated. Holes also collapse on their own over time.

• Consider relocating hoses or other hazards away from dense nesting areas. Mark holes to avoid tripping.

• Control weeds and improve drainage in your lawn. Dense roots deter tunneling and reduce suitable nest sites.

Appreciating the Importance of Ground Bees

Ground bees truly are valuable native pollinators that deserve our tolerance and protection. By better understanding their biology and implementing a few practical precautions, we can easily coexist with these misunderstood insects. Welcoming ground bees and other wild pollinators into our landscapes supports natural biodiversity and a healthy environment we all benefit from.