Dozens of flying insect species dig into the ground at some stage of their lives, but the ones you are most likely to notice are solitary bees, digger wasps, dung beetles, and certain flies. Of these, ground-nesting bees are by far the most common culprit behind the small, mysterious holes that appear in lawns, garden beds, and sandy paths each spring. The answer changes depending on where you live, the season, the soil type, and the size of the holes, so identifying the right group matters if you want to know whether to leave them alone or take action.
Ground-Nesting Bees
Most people picture bees living in hives, but the majority of the world’s roughly 20,000 bee species are solitary, and a huge proportion of those nest underground. Common genera you might encounter include Andrena (mining bees), Colletes (plasterer bees), Halictus and Lasioglossum (sweat bees), and Nomia (alkali bees). A single female digs a narrow shaft into the soil, carves out one or more small chambers at the bottom, stocks each chamber with a ball of pollen and nectar, lays an egg on it, and seals it up. She then repeats the process, sometimes digging multiple burrows in a season.
What often startles homeowners is that these bees tend to nest in aggregations. Hundreds or even thousands of individual holes can appear in a patch of bare ground over the course of a few weeks. A citizen-science project in the UK collected nearly 400 reports from the public in a single season, and about 60 percent of those turned out to be active nesting aggregations, with some species favoring sloped, sunny sites and others preferring flat, shaded spots.1Ecosphere. Using citizen science to examine the nesting ecology of ground‐nesting bees Despite looking alarming from above, these bees are gentle. Solitary females rarely sting because they have no colony to defend.
Burrow architecture varies by species. Solitary species tend to create simple, linear, unbranched tunnels that are used once and then gradually collapse, while social ground-nesting species build more complex, branched systems that get reused.2Geoderma. Morphology and temporal evolution of ground-nesting bee burrows created by solitary and social species quantified through X-ray imaging The entrance is typically a pencil-width hole surrounded by a small mound of excavated soil, sometimes called a “tumulus.”
Digger Wasps
Solitary wasps are the other large group of flying insects that regularly excavate ground nests. The family Sphecidae includes several well-known digger wasps, particularly species in the genus Ammophila (thread-waisted sand wasps), Sphex (great golden digger wasps), and Philanthus (beewolves). Like solitary bees, each female works alone. She digs a nearly vertical burrow ending in an elliptical cell, hunts a specific type of prey, paralyzes it with a sting, drags it into the cell, lays an egg on it, and seals the entrance.3Animal Biology. Nesting and mating behaviours, and the development time of three solitary digger wasps of the genus Ammophila (Hymenoptera: Sphecidae)
The prey they choose is one of the easiest ways to tell digger wasps apart from ground-nesting bees. If you see an insect carrying a caterpillar, grasshopper, or spider into a hole, it is almost certainly a wasp. Ammophila species provision their cells with one or two caterpillars, while Philanthus species hunt other bees and Bembix species catch flies. Female body size correlates with both egg size and the size of prey she provisions, so larger females tend to dig bigger burrows stocked with larger victims.4Canadian Journal of Zoology. Egg size, prey size, and sexual size dimorphism in digger wasps (Hymenoptera: Sphecidae)
An interesting behavioral detail is that Ammophila wasps temporarily close their nest entrance just below ground level when they leave to hunt, then permanently seal the burrow at or above the cell once provisioning is complete.3Animal Biology. Nesting and mating behaviours, and the development time of three solitary digger wasps of the genus Ammophila (Hymenoptera: Sphecidae) This means the holes you see are active, in-progress nests. Once a wasp finishes, the entrance vanishes.
Dung Beetles and Other Burrowing Beetles
Dung beetles are strong fliers, and many species dig tunnels directly beneath or near a dung pat, rolling or dragging dung underground to form brood balls where their larvae develop. The tunneling species (as opposed to the dung-rollers you might picture from nature documentaries) excavate vertical shafts and bury brood balls at depths that can reach around 20 cm, with terminal depth depending partly on how compacted the soil is.5Applied Soil Ecology. Dung beetles can tunnel into highly compacted soils from reclaimed mined sites in eMalahleni, South Africa Some species adjust their strategy depending on moisture: in dry soil, the beetle Euoniticellus intermedius produces clumps averaging nearly nine brood balls per tunnel and lines the tunnel walls with dung to prevent collapse, while in moist soil it produces brood balls singly across multiple tunnels.6Australian Journal of Entomology. Effect of soil moisture on brood ball production by Onthophagus binodis Thunberg and Euoniticellus intermedius (Reiche) (Coleoptera: Scarabaeinae)
Dung beetle legs are physically adapted for this lifestyle. Different species show measurably different joint angles and orientations of the basal leg segment depending on whether they are tunnelers, rollers, or dwellers, reflecting how deeply burrowing has shaped their anatomy.7PubMed. Functional leg design in dung beetles: Morphological adaptations to food relocation behavior Other beetle families also burrow. Tiger beetles, for instance, lay eggs in soil burrows where the larva waits at the surface to ambush passing prey, and Japanese beetles spend most of their life cycle underground as grubs before emerging as flying adults.
Flies That Go Underground
Several true flies in the order Diptera have a ground-burrowing stage, though it is usually the larva, not the flying adult, that does the digging. Blowfly larvae of the species Chrysomya megacephala, for example, burrow into loose soil when they are ready to pupate. Experiments have shown that third-instar larvae can move through soil both upward and downward, with pupation success dropping as burial depth increases.8PubMed Central. Study on ascending and descending vertical dispersal behavior of third instar larvae of Chrysomya megacephala (Fabricius) (Diptera:Calliphoridae): An evidence that blowflies survive burial
A more unusual case involves the fly Muscina angustifrons, whose larvae feed on mushroom fruiting bodies, then travel 10 to 20 cm horizontally from the feeding site before burrowing up to 6 cm underground to pupate. These wandering larvae carry fungal spores in their guts, which they excrete at their pupation sites, effectively planting mycorrhizal fungi underground.9Mycoscience. Soil burrowing Muscina angustifrons (Diptera: Muscidae) larvae excrete spores capable of forming mycorrhizae underground So while the adult fly does the flying and the egg-laying, the larval stage is what physically enters the soil.
Soil conditions heavily influence how well fly larvae develop underground. Moisture is the single most influential factor for species like Megaselia scalaris and Dohrniphora cornuta, with moderate moisture levels around 20 to 40 percent being the sweet spot for successful growth and timely development.10PubMed Central. The Effect of Soil Type and Moisture on the Development of Forensically Important Megaselia scalaris and Dohrniphora cornuta (Diptera: Phoridae)
Cicadas and Their Long Underground Lives
Cicadas are probably the most dramatic example of a flying insect tied to the ground, even though it is the wingless nymph that actually lives in the soil. After the adult female lays eggs in tree branches, the newly hatched nymphs drop to the ground and burrow into the soil, where they feed on root sap for years. Prairie cicada nymphs (Cicadetta calliope) collected from sandy soils were observed burrowing immediately when placed in experimental enclosures, excavating air-filled cells roughly 20 to 40 mm long and averaging 9 mm wide.11PALAIOS. Traces and burrowing behaviors of the cicada nymph Cicadetta calliope: Neoichnology and paleoecological significance of extant soil-dwelling insects
Some tropical species take this even further. Nymphs of Guyalna chlorogena in South America build elaborate clay turrets 20 to 40 cm tall above their vertical burrows during the final year of larval life. These turrets appear to regulate temperature and humidity inside the tunnel. The nymph actively maintains, repairs, and rebuilds the turret as needed, and opens and closes it on a set schedule before finally emerging to molt into a winged adult.12Ecosystem and Biodiversity of Amazonia. The Nymph Architect of the Cicada Guyalna chlorogena: Behaviours and Ecosystem The pencil-sized exit holes that periodically appear in lawns across eastern North America are the handiwork of periodical cicadas emerging after 13 or 17 years underground.
Mole Crickets and Antlions
Mole crickets are heavily built, winged crickets whose forelegs are modified into broad, shovel-like tools for digging. They spend most of their lives underground, creating tunnels through moist soil, and fly mainly at night during mating season. Research on Gryllotalpa orientalis documented four distinct vibration behaviors used underground, including scraping with the forelegs, tapping with the forelegs, tapping with mouthparts, and whole-body tremulation, with the scraping behavior hypothesized to be an inspection method for evaluating burrow conditions.13PubMed Central. Four types of vibration behaviors in a mole cricket Mole crickets are a serious turfgrass pest in the southeastern United States and many tropical regions because their tunneling uproots grass and dries out the root zone.
Antlions are less obviously “burrowing” but equally ground-dependent. The adult antlion is a delicate, lacewing-like flier, but its larva digs conical pit traps in sandy soil and buries itself at the bottom, jaws exposed, waiting for ants and other small insects to tumble in. Researchers have found that the larva uses its head and mandibles as a backward-directed catapult to fling sand at prey, causing miniature landslides that drag victims toward the center of the pit.14PubMed Central. Antlion larvae follow optimality rules in body orientation during sand tossing The sand-throwing also serves as constant maintenance: finite-element modeling showed that the behavior keeps the pit slope near its critical angle, so the trap stays maximally efficient between captures.15PubMed Central. Sand-throwing behaviour in pit-building antlion larvae: insights from finite-element modelling
Why Soil Type and Bare Ground Matter
If you have ever wondered why ground-nesting insects pick one patch of yard and ignore another, the answer usually comes down to soil. Bee species show enormous variation in their preferences for soil texture, compaction, moisture, temperature, and ground-surface features.16Ecological Entomology. Nesting habitat of ground‐nesting bees: a review As a general rule, more bare ground and more sand mean more ground-nesting bees. A study of 131 plots across 35 farms collected over 8,600 ground-nesting bees from 100 species and found that abundance and species richness both rose with higher percentages of bare ground and sand.17Insect Conservation and Diversity. Associations between soil characteristics and ground‐nesting bees on farms Compaction and slope also mattered, but the relationships were highly species-specific, meaning different bees prefer different conditions.
This is why garden paths, dry embankments, patchy lawns, and sandy flower beds are hot spots for nesting activity. A thick, well-watered, heavily mulched lawn rarely attracts ground-nesters because it offers nothing they need. If you want to discourage nesting, keeping the soil covered with mulch or dense vegetation is usually enough. Conversely, if you want to support ground-nesting pollinators, leaving some areas of undisturbed bare soil is one of the simplest things you can do.
Ecological Benefits of Insect Burrows
It is tempting to view insect holes in the ground as damage, but the ecological payoff of all this burrowing is substantial. Ground-nesting bees create vertical macropores in the soil similar to those made by earthworms. These tunnels persist for months and improve water infiltration and gas transport by creating preferential pathways for both water and air, extending oxygen-rich conditions deeper into the soil.18Basic and Applied Ecology. Beyond pollination – The neglected contribution of ground-nesting bees to soil functions In clay-heavy or compacted soils, this aeration can meaningfully improve plant-root health.
The pollination dimension is even more important. About 87 percent of all flowering plants require animal pollinators, and ground-nesting bees are among the most important groups providing that service. Without these pollinators, the soil itself would lose ecosystem services that depend on those flowering plants, including litter inputs, shading, root networks that stabilize soil structure, and erosion control.19PubMed Central. Regard and protect ground-nesting pollinators as part of soil biodiversity Dung beetles provide a parallel benefit underground by burying organic matter, improving nutrient cycling, and reducing fly-breeding habitat in pastures.
Uninvited Guests in Ground Nests
Wherever ground-nesting bees and wasps dig, parasites and freeloaders follow. Velvet ants (family Mutillidae) are actually wasps whose wingless females look like fuzzy ants. They prowl the ground searching for the nests of solitary bees and wasps, enter the burrows, and lay their eggs on the host’s brood. Research into host relationships suggests an intense association between velvet ants and several ground-nesting families, particularly crabronid and sphecid wasps along with certain bee subfamilies, likely because these hosts nest in aggregations that make them easier to locate.20PubMed. Environmental Heterogeneity in Parasitoid-Host Interaction for Mutillidae (Hymenoptera: Apocrita)
Cuckoo bees are another common group of brood parasites. Like the bird they are named after, a female cuckoo bee enters another bee’s nest, lays her egg, and lets the host’s food provisions feed her larva instead. Bee flies (family Bombyliidae) take a different approach: the adult hovers above a nest aggregation and flicks her eggs toward the burrow entrances. These parasitic relationships are one reason you sometimes see a surprising variety of flying insects hovering around a nesting site even though only one or two species are actually digging.
How to Tell What Is Nesting in Your Yard
If you have found holes in the ground and want to figure out what made them, a few clues help narrow it down:
- Hole diameter: Pencil-width holes (4 to 8 mm) with small soil mounds usually mean solitary bees. Slightly larger holes with no mound, or holes with a smooth interior, point to digger wasps. Dime-sized or larger holes may be cicada exit tunnels or mole cricket burrows.
- Soil mound shape: A symmetrical ring of loose soil around the entrance is classic for mining bees. A crater-like depression in sand suggests an antlion pit, not a burrow at all.
- Time of year: Spring aggregations of small holes are almost always solitary bees. Summer holes with wasps carrying prey are digger wasps. Late spring or early summer holes appearing suddenly by the hundreds, with no insect visible at the entrance, are likely cicada emergence holes.
- Insect behavior: If you see an insect hovering low over the ground and repeatedly landing at the same spot, it is likely a nesting bee or wasp. If you see something carrying a paralyzed insect or caterpillar, it is a wasp.
In the vast majority of cases, the best course of action is to leave the insects alone. Ground-nesting bees and digger wasps are not aggressive, nesting activity is temporary (usually a few weeks), and the ecological benefits are real. If you are dealing with mole crickets damaging turfgrass, that is a genuinely different situation worth managing, but for bees and wasps the “problem” resolves itself quickly and no treatment is needed. Pest-control sprays applied to solitary bee aggregations kill pollinators that your garden depends on while solving a problem that was never really a threat.
When Burrowing Insects Colonize Unexpected Places
Ground-nesting insects are resourceful about finding suitable substrate, and that sometimes leads to conflicts. Solitary bees and wasps will nest in the sand between patio pavers, in the mortar joints of old brick walls, in potted plants with exposed sandy soil, and along the edges of gravel driveways. Sports fields with sandy infields sometimes host large nesting aggregations. In all these cases the insect has simply found bare, well-drained, sun-warmed substrate that matches its preferences.
Re-covering the area with mulch, gravel, or dense plantings is usually sufficient to redirect nesting elsewhere. Watering the area heavily can also discourage species that prefer dry conditions. The key insight is that ground-nesters are not infesting your property the way termites or carpenter ants might. They are surface-nesting transients who chose a spot because it had the right soil and light conditions. Change those conditions and they move on, no chemicals required.