Most bees don’t live in hives at all. The majority of the world’s bee species raise their young in the ground, so the small holes and soil mounds in a lawn or garden bed are often the work of bees rather than pests. These ground bees are a very different animal from honey bees, and from the yellow jackets that also nest underground.
Most Bee Species Nest in the Ground
Of the more than 20,000 bee species in the world, about 70% build their nests underground.1Pollinators. Ground Nesting Bees – What to Look for and What Species to Expect Most of these live largely solitary lives, with each female digging and stocking her own nest rather than sharing a hive.2The Bee Conservancy. Ground Nesting Bees – The Bee Conservancy The honey bee hive most people picture is the unusual arrangement among bees.
A solitary mother digs a tunnel and builds side cells, places a ball of pollen mixed with nectar in each one, and lays an egg on it. After she seals the cells she never feeds the young again, because the larvae live off the food she left. Most solitary mothers die within weeks, so the young never meet her. Since each hole belongs to one mother, a patch with many holes is many separate nests, not one colony.
Honey bees nearly always nest in cavities such as hollow trees or wall voids, not in burrows dug in a lawn. A bee going in and out of a small soil hole is almost certainly another kind of bee, usually a single female digging, foraging, and laying eggs all by herself.
You may meet a few kinds in your yard. Mining bees often appear on lawns in early spring. Sweat bees are small and sometimes metallic green.
Bumble bees are the social exception: large, fuzzy, and living together in a single nest. They often move into abandoned rodent dens underground or under tufts of grass.3Bumble Bee Nest Quest. Bumble Bee Nest Quest – Bumble bee nesting 101 Rodents line these dens with grass, stems, and fur that insulate the nest and help hold its temperature.4Bumble Bee Nest Quest. Bumble Bee Nest Quest – Bumble bee nesting 101 A bumble bee colony in the ground lasts one growing season, and the nest is not reused the next year.
What a Ground Bee Nest Looks Like
On the surface, each entrance is a round hole about the width of a pencil. It is often ringed by a little volcano of loose soil the bee pushed out while digging. On sunny mornings, bees fly low and zigzag over the patch, searching and landing near their holes. That is normal behavior, not aggression. A patch can hold a handful of holes or dozens to hundreds, and the mounds may vanish after rain, so the spot can look different from day to day. Nests are often packed closely together because good soil is patchy, so many females pick the same patch.
Ants and worms can leave similar-looking signs. Ant mounds have many ants walking, not flying. Worm castings are crumbly lumps with no flying insects around them. Seeing a bee enter or leave the hole confirms it.
Below the surface, ground bees dig tunnels that lead to tiny cells where young bees develop.5Bee Better Certified®. Digging Deep: An inside look at how bees nest Most nest cells sit 6 to 16 inches below the surface.6Bee Better Certified®. Digging Deep: An inside look at how bees nest Some bees that reuse existing nests have tunnels that run dozens of feet underground.7Bee Better Certified®. Digging Deep: An inside look at how bees nest So stepping on or mowing over a nest usually doesn’t reach the young bees.
Are Ground Bees Dangerous
In a busy cluster of ivy bee nests, a person standing, walking and gardening for 10 hours was stung only once.8Journal of Apicultural Research. Stinging risk and sting pain of the ivy bee, Colletes hederae Bees bumped into the person about 6 times an hour, mostly harmless collisions.9Journal of Apicultural Research. Stinging risk and sting pain of the ivy bee, Colletes hederae The ivy bee’s sting often can’t get through human skin, piercing fingertips only half the time.10Journal of Apicultural Research. Stinging risk and sting pain of the ivy bee, Colletes hederae When it does sting, the pain is closer to a nettle than a honey bee sting and fades in about 10 minutes.11Journal of Apicultural Research. Stinging risk and sting pain of the ivy bee, Colletes hederae Gardening, mowing, and play near such nests is generally safe.
Solitary bees are gentle because there is nothing worth defending as a group. Males often patrol over the nest patch, which looks threatening, but they have no stinger and cannot sting. Females generally sting only when pressed or trapped, such as when stepped on with a bare foot or squeezed in a hand.
Walking through a patch can feel odd, since bees bump into you or hover close. They are usually males or females checking you out. Standing still or walking calmly past is fine, while swatting is more likely to lead to a bad encounter. A mower can pinch a bee sitting on the surface, but mowing over a patch is generally safe for people.
A few sensible habits help. Wear shoes over a nest patch during flight season, and teach children not to grab or swat the bees. Anyone with a known sting allergy should still avoid handling bees and keep their medication handy.
Ground Bees Versus Yellow Jackets
Bees are usually stout and hairy, while wasps are slender and much less hairy.12Pollinator.org. Bees Vs Wasps That’s because bees carry branched hairs that trap pollen so females can carry it back to the nest, and wasps lack them.13Pollinator.org. Bees Vs Wasps There are exceptions: some cuckoo bees, which lay eggs in other bees’ nests, are nearly hairless and look like wasps.14Pollinator.org. Bees Vs Wasps Wasps such as yellow jackets can also sting repeatedly without losing their stinger.15Witt Pest Management. The Dangers Of A Yellow Jacket Ground Nest
Yellow jackets are smooth, shiny, and slim-waisted with sharp black-and-yellow bands. Most ground bees look fuzzier and stouter, and are often brown, black, or dull-colored. Yellow jackets are drawn to meat, sweet drinks, and picnic food, whereas ground bees visit flowers for pollen and nectar. Body color alone isn’t a dependable test, so combine it with the nest entrance and behavior.
The nest tells you more. Ground bee nests are usually many small separate holes, each used by a single bee, with only a few bees coming and going at a time. A yellow jacket nest usually has one larger entrance with a steady stream of insects flying in and out. The colony grows through the season, and by late summer it can be large and much more defensive. Disturbing the entrance, even by vibration from mowing nearby, can bring many attackers at once.
A single busy hole with shiny black-and-yellow insects suggests yellow jackets. Don’t pour liquids into the entrance or block it yourself. That is the case for a professional. Ground bee clusters rarely need any removal.
Why Bees Chose Your Yard
More bee nests appear where soil is warmer and plant cover is low.16Journal of Pollination Ecology. The importance of soil and vegetation characteristics for establishing ground-nesting bee aggregations Some species also favor spots with brighter light, an uneven surface, and nearby landmarks.17Ecological Entomology. Nest site preference and success in a gregarious, ground‐nesting bee Dieunomia triangulifera Preferences vary hugely between species, from sandy to compact or moist soil.18Ecological Entomology. Nesting habitat of ground‐nesting bees: a review In one test of different soil conditions, no single factor decided where bees nested, so many species manage in a range of soils.19Ecosphere. Soil sanctuaries: Experimental manipulations enhance ground‐nesting bee habitat Thin patches of lawn, sunny banks, and bare garden edges are typical nest sites.
If bees suddenly appear in your lawn, thin or patchy turf is a likely reason, since it exposes the bare soil many bees need for digging. Sunny, south-facing slopes warm quickly in spring, so they are often the first places bees choose. Bees also come back to the same good patch year after year, because the young emerge near where they were raised.
If you’d rather not have them, thicken the turf by overseeding, or cover the bare patch with mulch, once the season ends so the soil is less open next year. Regular watering can make the soil less inviting to some species, though it won’t work for all kinds. Wait until the bees finish flying for the year before changing the spot, so you don’t harm the young below.
Why Leaving Them Alone Helps
Several ground-nesting bees are proven crop pollinators, and the alkali bee is managed on a large scale for alfalfa.20PubMed. The Extraordinary Alkali Bee, Nomia melanderi (Halictidae), the World’s Only Intensively Managed Ground-Nesting Bee Their digging also moves and mixes soil, adding pores that help water and air move into the ground.21Basic and Applied Ecology. Beyond pollination – The neglected contribution of ground-nesting bees to soil functions Native ground bees are among the burrowers that help rain soak into soil.22Restoration Ecology. Restoration of an Ecosystem Function to Revegetation Communities: The Role of Invertebrate Macropores in Enhancing Soil Water Infiltration
Tilled fields have fewer and less varied ground bees than untilled field edges.23Insect Conservation and Diversity. Tillage in southeastern US row crops reduces ground‐nesting bee incidence and diversity compared to field edges Soil-nesting bees also decline as paved and built-over surface increases, while above-ground nesters are barely affected.24Urban Ecosystems. Urban development reduces bee abundance and diversity Chemicals matter too: squash bees exposed to a crop treated with a soil-applied insecticide started 85% fewer nests and produced 89% fewer young.25PubMed Central. Population decline in a ground-nesting solitary squash bee (Eucera pruinosa) following exposure to a neonicotinoid insecticide treated crop (Cucurbita pepo)
Many garden habits are aimed at flower-visiting bees, such as planting blooms and avoiding spray on flowers, and they don’t cover the soil where these bees live. Pavers, thick mulch, and landscape fabric cover the ground and block bees from digging, so the loss is gradual and easy to miss.
A gardener can help in a few ways. Skip soil-drench insecticides near areas where bees nest, because the chemical sits in the soil where they live. Plant flowers nearby so females have pollen close to the nest and spend less time flying. Leave some bare, sunny ground unmulched so new nest sites remain available.
How Long Ground Bees Stay
Many mining bees fly in early spring for about four to six weeks, and then the activity stops. Other species appear later, with some, such as ivy bees, flying in late summer or autumn. After the flight season ends, the holes disappear and the lawn looks normal again. The next generation emerges from the same patch the following year, which is why a spot can seem to have bees come back.
Underground, young bees spend most of the year developing and resting inside their soil cells. The eggs hatch and the larvae feed on the pollen stored in the cell, then develop into adults. The new adults often stay in the cell through winter and chew out when the weather warms. In at least one ground bee, helpful bacteria in the cells block harmful fungi while the young wait out winter.26PubMed Central. Symbiotic bacteria and fungi proliferate in diapause and may enhance overwintering survival in a solitary bee Disturbing soil during that time can harm them, and it can delay when surviving young emerge.27Agriculture, Ecosystems and Environment. Impact of tillage on the crop pollinating, ground-nesting bee, Peponapis pruinosa in California Mark the patch so you avoid tilling it in the off-season, and expect bees back next year if conditions stay the same.