Yes, pest control can get rid of gnats, but the approach matters more than you might expect. Most gnat infestations stem from a moisture or organic-matter source that keeps producing new generations, so simply spraying adults won’t solve the problem. A professional exterminator costs $150 to $300 on average, and the real value is in identifying and treating the breeding source rather than just killing the gnats you can see.
Why Gnats Keep Coming Back
The gnats swarming around your kitchen or houseplants are almost always fungus gnats, drain flies, or fruit flies. Each one breeds in a specific environment: fungus gnats lay eggs in moist potting soil, drain flies reproduce in the organic film inside pipes, and fruit flies breed on overripe produce or fermenting residue. The adults you swat are only a fraction of the population. Larvae and eggs hidden in soil, drains, or decaying material are constantly replacing them.
This is the core reason DIY efforts often stall. A vinegar trap or store-bought spray kills the gnats in front of you, but it doesn’t reach the nest beneath the soil or the breeding site inside a drain. Homeowners frequently stop treating once visible activity drops, only to see a new wave emerge days later. The breeding source, along with the moisture and organic matter feeding it, stays intact.
What Professional Treatment Looks Like
A pest control technician starts by identifying the species and locating the breeding source. That step alone can be worth the cost, because treating the wrong spot wastes time and money. Once the source is confirmed, professionals use a layered strategy that targets both larvae and adults.
For fungus gnats breeding in soil, the most effective professional tools are biological. Insect-killing nematodes (microscopic roundworms) are applied as a soil drench. They actively hunt gnat larvae in the top layers of moist soil, reproduce on their own, and can provide season-long control after a few initial applications as long as soil stays moist and temperatures are between 60° and 90°F. Predatory mites are another option: small, light-brown mites that feed on gnat larvae and pupae in the upper soil layer.
Professionals also use a naturally occurring bacterium called Bti, which is toxic only to fly larvae like mosquitoes, black flies, and fungus gnats. It’s safe around people and pets. For heavy infestations, Bti is applied at higher concentrations as a soil drench. Insect growth regulators are another professional-grade tool: these compounds prevent larvae from developing into adults, breaking the breeding cycle without broad-spectrum pesticides.
When populations are extremely high and fast knockdown is needed, technicians may spray pyrethrins (a plant-derived insecticide with low toxicity to people and pets) on soil surfaces and areas where adults rest. Synthetic versions of the same compound tend to be more effective and longer-lasting. These provide quick visible relief while the biological controls work on the larvae below the surface.
How Long Treatment Takes
Don’t expect a single visit to end the problem overnight. Gnat eggs already in the soil will continue to hatch for days after treatment, so you’ll likely see some adults for one to two weeks even after a successful application. Biological controls like nematodes need time to establish populations and hunt down larvae. Growth regulators work by preventing the next generation from maturing, which means the current crop of adults has to die off naturally.
Most professionals plan for at least one follow-up visit to assess whether the breeding source has been fully addressed. If the initial application used Bti, repeat treatments are often needed because its effects are temporary. Nematodes, by contrast, can self-sustain in moist soil after several initial applications. A realistic timeline for full eradication is two to four weeks, assuming the moisture source is also corrected.
When Professional Help Is Worth It
For a small cluster of fungus gnats around one houseplant, professional pest control is probably overkill. Letting the soil dry out between waterings and using a store-bought Bti product can handle minor cases. Where professionals earn their fee is in situations with multiple breeding sites, gnats appearing in rooms with no obvious source, or infestations tied to structural moisture problems like leaky pipes, damp crawl spaces, or poorly draining planters.
Misidentifying the pest is another common failure point for DIY efforts. Drain flies require a completely different treatment than fungus gnats, and fruit flies won’t respond to soil drenches at all. If you’ve been trying home remedies for more than a couple of weeks without improvement, the species or the breeding source (or both) may not be what you think.
At $150 to $300 for a typical treatment, professional gnat control is on the lower end of extermination costs. Annual pest control plans that include gnat coverage run $300 to $900 per year depending on visit frequency. Some companies charge as little as $100 for a straightforward case, though severe or hard-to-reach infestations can push costs up to $900.
Preventing Gnats After Treatment
Professional treatment eliminates the current population, but gnats will return if the conditions that attracted them don’t change. The single most important factor is moisture. Overwatered houseplants are the leading indoor breeding ground for fungus gnats. Letting the top inch or two of soil dry completely between waterings removes the moist environment larvae need to survive.
For drain-related gnats, cleaning the organic buildup inside sink and shower drains is essential. A stiff brush and enzymatic drain cleaner work better than bleach, which only treats the surface. Fix any leaking pipes, especially under sinks or in crawl spaces, because even small amounts of standing water or persistently damp wood can sustain a breeding population.
If you use potting soil, choose mixes that drain well and avoid bags that have been sitting open and damp, as they can already contain gnat eggs. A layer of coarse sand or decorative gravel on top of the soil in potted plants creates a dry barrier that discourages egg-laying. For ongoing biological protection, nematode drenches can be reapplied seasonally to keep larval populations in check without any chemical residue.