What Eats Gnats? Natural Predators and How to Attract Them

Gnats are eaten by a surprisingly wide range of animals, from dragonflies snatching them mid-air to tiny soil mites ambushing their larvae underground. The list of natural gnat predators spans spiders, beetles, fish, nematodes, and even carnivorous plants. Understanding which predators target gnats at each life stage is the key to attracting the right allies, whether you are managing a backyard, a greenhouse, or a few houseplants on a windowsill.

Dragonflies and Aerial Hunters

If you have ever watched a dragonfly patrol a pond at dusk, you have watched a gnat predator at work. Dragonflies are among the most efficient aerial hunters of small flying insects, including gnats, midges, and mosquitoes. A study tracking dragonfly attacks on insect swarms over 19 evenings recorded more than 1,350 attacks by two dragonfly species during the observation periods, with predation events concentrated in the first 15 minutes after swarms formed.¹ Dragonflies hunt on the wing with remarkable precision, picking off individual insects from dense clouds of them.

Bats fill a similar niche after dark. Many insectivorous bat species consume enormous quantities of small flies each night, using echolocation to zero in on gnats and midges that gather near lights or water. Swallows, purple martins, and other aerial-feeding birds also eat gnats during daylight hours, sweeping through swarms with open mouths. If you want to attract these predators, the approach is habitat-based: a small pond or water feature draws dragonflies (they need standing water to breed), while bat boxes mounted on a south-facing wall or tree can encourage roosting. Leaving some wild or unmowed areas near water gives dragonflies perching spots and shelter.

Web-Building Spiders

Spiders do not chase gnats. They wait. And they are very good at it. Research on the prey captured by web-building spiders found that Nematocera, the suborder that includes gnats, midges, and mosquitoes, ranked as one of the most important prey groups for both orb-weaving spiders and sheet-weaving spiders.² That makes sense when you think about it: gnats are small, weak fliers that blunder into webs easily, and they tend to fly in large numbers near the ground or around vegetation, right where many spiders build.

The design of the web matters. Experiments testing different web structures showed that each web type has an optimal thread density for capturing small flies like fruit flies and gnats, with capture rates peaking at specific densities before dropping off again.³ In rice paddies, where gnats and midges emerge in waves from flooded fields, spiders shift their diet seasonally to rely heavily on these insects, using them as a major food source early in the growing season before herbivorous prey becomes available.⁴

Encouraging spiders around your home or garden is mostly about leaving them alone. Resist the urge to knock down every web you see in corners of porches, garages, or garden sheds. Spiders positioned near outdoor lights are especially useful because lights attract gnats at night, effectively creating a buffet line that ends in silk. If you keep houseplants and deal with fungus gnats indoors, a small cellar spider in the corner is more friend than foe.

Predatory Soil Mites

Many gnat species, especially fungus gnats, spend most of their lives as larvae in moist soil. That is where some of their most effective predators live. The predatory mite Stratiolaelaps scimitus (often sold under an older name, Hypoaspis miles) is a tiny soil-dwelling mite that feeds on fungus gnat larvae. It is widely used in greenhouse production and is commercially available for home gardeners. Lab research confirmed that these mites can successfully develop and reproduce when fed exclusively on fungus gnat larvae.⁵

These mites live in the top layer of soil and actively hunt gnat larvae. They are nearly invisible to the naked eye and do not bite people, damage plants, or leave the pot. You can buy them online or at garden centers, usually shipped on a carrier material like vermiculite that you sprinkle over the soil surface. They work best as a preventive measure or in combination with other controls, because they eat larvae one at a time rather than wiping out a whole population overnight. Keep the soil slightly moist (but not waterlogged) to give them a hospitable environment. They are a particularly good fit for houseplants and indoor container gardens where chemical sprays are impractical or unwanted.

Rove Beetles

The rove beetle Dalotia coriaria is another commercially available predator that targets fungus gnat larvae in soil. These small, dark beetles are fast-moving and aggressive feeders. In greenhouse experiments, pots where even a single rove beetle adult was released produced roughly half as many adult fungus gnats as untreated controls.⁶

Rove beetles have a practical advantage over predatory mites: they can fly. That means they actively disperse through a greenhouse or garden to find prey, rather than waiting for larvae to wander past. They also eat thrips larvae and other small soil pests, making them useful generalists. Like the mites, they are harmless to people and plants. They prefer moist growing media and do best when there is some organic matter on the soil surface for shelter.

One important consideration is pesticide compatibility. Testing of various reduced-risk pesticides found that some common insecticides, including acetamiprid, lambda-cyhalothrin, and cyfluthrin, killed rove beetle adults outright. But certain biological and organic products, such as azadirachtin, organic oils (cinnamon, rosemary, thyme, and clove), and the fungal agent Beauveria bassiana, were nontoxic to the beetles.⁷ If you are using rove beetles as biocontrol, you need to choose any accompanying sprays carefully, or you risk killing your predators along with the gnats.

Parasitic Nematodes

Entomopathogenic nematodes are microscopic roundworms that infect and kill insect larvae in soil. They are not predators in the usual sense; they enter a larva’s body, release bacteria that kill the host, and then feed and reproduce inside it. Several species are effective against fungus gnat larvae and are sold as biological control products for both commercial greenhouses and home use.

Steinernema feltiae is the most commonly recommended species for fungus gnats. Research on floriculture crops showed that applications of this nematode significantly reduced fungus gnat populations compared to untreated controls.⁸ However, the choice of nematode species matters more than many product labels let on. A study comparing several nematode species in different potting mixes found that S. feltiae sometimes provided only short-lived control, with its effect lasting just about a week in one growing medium, while certain Heterorhabditis species suppressed fungus gnat emergence for the entire 63-day observation period.⁹

The practical takeaway is that the potting medium and temperature affect which nematode species works best. S. feltiae tolerates cooler conditions and is a solid all-purpose choice, but if you are dealing with a persistent infestation in warm conditions or peat-based mixes, a Heterorhabditis species may give longer-lasting results. Nematodes are typically mixed into water and applied as a soil drench. They need moist (not dry) soil to move and find hosts, and they are sensitive to UV light, so apply them in the evening or on overcast days. They are completely harmless to people, pets, and plants.

Fish and Aquatic Predators

Many gnat and midge species have aquatic larvae. Fungus gnats breed in moist soil, but their close relatives, including non-biting midges and black flies, develop in standing or slow-moving water. That is where fish come in. Research in freshwater marshes found that small insectivorous fish, including juvenile carp and brown bullhead, significantly reduced midge larval densities once they became abundant from spawning.¹⁰

For backyard ponds, mosquitofish and certain minnow species serve the same role. They cruise the shallows eating gnat and midge larvae along with mosquito wrigglers. Even goldfish and koi eat insect larvae, though they tend to be less efficient than smaller, faster species. If you have a rain barrel or ornamental water feature that seems to breed gnats, stocking it with a few small fish or adding a fountain to keep the water moving can make a big difference. Moving water discourages egg-laying by many gnat species, and any fish present will clean up the larvae that do hatch.

Aquatic invertebrates are also worth mentioning. Dragonfly and damselfly nymphs, which live underwater for months or years before becoming adults, eat gnat and midge larvae voraciously. So do backswimmers, water beetles, and various aquatic mites. A healthy, biodiverse pond with submerged vegetation and minimal pesticide exposure will naturally develop a community of these predators.

Carnivorous Plants

Sundews, butterworts, and pitcher plants all capture gnats, and they have become popular among houseplant enthusiasts partly for that reason. Sundews trap insects on sticky, glistening droplets at the tips of tentacle-like leaves. Butterworts work on a similar principle, with flat, sticky leaves that curl slightly when an insect lands. Pitcher plants use a pitfall trap: gnats tumble into a fluid-filled tube and drown.

The appeal is obvious, but a note of realism: these plants catch gnats passively, not by luring them. A field and lab study of the dwarf sundew (Drosera brevifolia) found that the plant was no better at capturing prey than neutral sticky traps placed nearby, suggesting that sundews do not actively attract insects to their leaves.¹¹ The researchers compared them to spider webs: both are passive adhesive surfaces that catch whatever stumbles into them. A single sundew on a windowsill will catch some fungus gnats, but it will not clear an infestation. Think of carnivorous plants as a supplemental layer rather than a standalone solution, and a fun one at that.

Combining Predators for Indoor and Greenhouse Settings

Fungus gnats are the gnat species that drives most people to search for predator-based solutions, because they breed in the moist potting soil of houseplants and greenhouse crops. The adults are mostly just annoying, but the larvae feed on root hairs and organic matter and can damage seedlings and young plants. A single biological control agent sometimes is not enough, especially in a warm, wet greenhouse where fungus gnats reproduce quickly.

The most effective approach combines predators that target different life stages. Predatory mites and rove beetles in the soil attack larvae, while parasitic nematodes infect and kill larvae from the inside. Yellow sticky traps near the soil surface catch egg-laying adults. If you are running a greenhouse, introducing both Stratiolaelaps mites and rove beetles gives you two independent predator populations working the same soil layer, and since the beetles are mobile fliers, they can redistribute themselves to wherever the gnat pressure is highest.

For houseplant owners working on a smaller scale, a tube of predatory mites sprinkled across your pots is the simplest starting point. Let the soil surface dry out between waterings (fungus gnat larvae need moisture to survive), add a layer of sand or gravel on top of the soil to discourage egg-laying, and the mites will handle much of the larval population below the surface. Nematode drenches can be applied a few times per year as a reset if the population gets ahead of you.

Why Gnats Matter in Food Webs

It is easy to view gnats purely as pests, but in natural ecosystems they are a critical link in the food chain. Gnats and midges often emerge from water or soil in enormous synchronized pulses, providing a concentrated burst of protein for predators at just the right time. In rice paddies, for instance, gnats and midges emerging from flooded fields form a major early-season food source for both web-building and ground-hunting spiders. Isotope analysis showed that these spiders relied on aquatic gnat and midge prey that carried carbon from algae and decomposing organic matter, effectively shuttling nutrients from the water into the terrestrial food web.⁴

This nutrient-shuttling role means that gnats connect aquatic and terrestrial ecosystems in ways that benefit agriculture. Spiders sustained by early gnat emergence go on to eat crop-damaging herbivores later in the season. Remove gnats entirely, and you may starve out the very predators that protect your plants from worse pests. That is a good reason to think about managing gnats, not eradicating them, and to favor biological control methods that reduce gnat populations to tolerable levels rather than wiping them out.

When Predator Timing Goes Wrong

One under-appreciated complication with relying on natural predators is timing. Many predator-prey relationships depend on seasonal synchrony: the predators need to be present and active when gnats are emerging. Climate shifts are altering this timing. Warming temperatures can cause insects to emerge earlier in the season or speed up their development, and if predators do not shift on the same schedule, the two populations fall out of sync.¹²

In practical terms, this means that a pond that once hosted dragonflies perfectly timed to intercept spring gnat swarms may lose some of that natural control if dragonfly emergence lags behind an earlier gnat hatch. For gardeners and greenhouse managers using purchased biocontrol agents, timing is something you control directly: you introduce the mites, beetles, or nematodes when you first notice gnat activity, rather than waiting for a natural predator to show up on its own schedule. That is one of the big advantages of commercial biocontrol over hoping for wild predators to do the job.

Gnat Larvae as Predators Themselves

Here is something most people do not expect: some gnat larvae are predators, not just prey. The cave-dwelling fungus gnat Macrocera nobilis builds elaborate silk webs inside the dark zones of caves in the eastern and central United States and uses those webs to capture other insects, mostly other small flies. The adults mate near cave entrances, but all egg-laying, larval development, and pupation happen in complete darkness.¹³ Their webs sometimes include bioluminescent elements, similar to the famous glowworms of New Zealand caves, which are actually a related group of fungus gnat larvae.

This reversal, gnat larvae acting as web-building predators of other insects, is a reminder that “gnat” covers a huge diversity of species with very different lifestyles. The tiny flies hovering around your kitchen compost are a world apart from the silk-spinning cave predators, even though both belong to the same broad group. That diversity also means that no single predator or control strategy works against all gnats. What eats a fungus gnat larva in potting soil is not the same thing that eats a biting midge over a salt marsh, and the predators you want to attract depend on which gnats you are dealing with and where they live.