Fruit Flies, Drain Flies and Fungus Gnats: Cost and Cure
Gnat treatment averages $200, drain flies up to $375. All three are source problems, and identifying which you have decides whether this costs nothing or $375.
Gnat and small fly treatment costs $100 to $300, with gnats averaging $200, fruit flies $150 to $300 and fungus gnats $100 to $150. A large drain fly infestation averages $375. These three are the pests most likely to be solved without paying anyone, because each has a single physical source and removing it collapses the population.
Fruit flies, drain flies and fungus gnats look similar enough to be treated identically and interchangeably, which is why treatment fails. They breed in three completely different places, and identifying which you have determines whether this costs you nothing or $375.
Telling the three apart
| Fruit flies | Drain flies | Fungus gnats | |
|---|---|---|---|
| Appearance | Tan to brown, often red eyes, rounded | Fuzzy, moth-like, held roof-shaped | Dark, slender, long legs, mosquito-like |
| Where seen | Kitchen, near fruit and bins | Resting on walls near drains | Around houseplants, weak flyers |
| Breeding site | Fermenting produce, bins, spills | Organic film in drains and traps | Damp potting soil |
| Flight | Quick, hovering | Short erratic hops | Drifting, often near soil |
| Typical treatment cost | $150 to $300 | Up to $375 if severe | $100 to $150 |
Contractor-reported ranges compiled by home services marketplaces in 2026, not federal statistics.
Why spraying does not work
All three are breeding in a medium, not living on surfaces. Killing the adults you can see does nothing to the larvae developing in the fruit bowl, the drain film or the plant pot, and a new generation emerges within days.
That is why a treatment applied without source removal reliably appears to fail. The company is not necessarily doing a poor job; the job is not the flies. It is the substrate.
This is one of the few pest categories where a good contractor may tell you not to buy a treatment. Our guide to integrated pest management covers why prevention-led programmes make that recommendation and why it aligns with their interests rather than against them.
Finding the source
- Fruit flies. Check overripe produce, the bottom of fruit bowls, bins and recycling, spills under appliances, and the drip trays beneath fridges. Beer and wine bottles left out are a common overlooked source.
- Drain flies. Tape a clear plastic bag or sticky note loosely over a suspect drain overnight. Flies trapped on the underside identify the drain. Check floor drains, rarely used showers, and basement or utility room traps.
- Fungus gnats. Let houseplant soil dry out further between waterings and check for saucers holding standing water. Yellow sticky cards near the soil confirm which plants are involved.
- If none of the above, look for a hidden moisture source: a slow leak under a sink, a damp subfloor, or a condensate line.
When it is worth paying
Professional treatment earns its price in a specific set of cases.
- The source is inaccessible, such as organic buildup deep in a waste line or a sewer defect. Drain flies from a broken line under a slab are a plumbing problem, and the cost reflects that.
- Commercial food premises, where small flies are an inspection and audit issue and documented control is part of what you are buying. Our guide to commercial pest control costs covers those contracts.
- Multiple simultaneous sources in a larger property, where systematic inspection beats guessing.
- It keeps returning after you have removed the obvious source, which usually means the real source has not been found.
Where the problem is a fruit bowl and a bin, paying $200 to treat it is buying a service you could have replaced with ten minutes of work. That is a legitimate thing to say and most cost guides will not say it.
Frequently asked questions
How much does it cost to get rid of gnats?
Gnat treatment averages $200, ranging $150 to $250. Fruit fly treatment costs $150 to $300, fungus gnats $100 to $150, and a large drain fly infestation averages $375. Minor infestations can be as little as $100, while severe widespread cases in larger properties reach $700 or more.
Why do fruit flies keep coming back after treatment?
Because the treatment killed adults while larvae continued developing in the breeding source. Fruit flies breed in fermenting produce, bins and spills, and a new generation emerges within days. Removing the source is what ends the problem; spraying without doing so reliably appears to fail.
How do I know if I have drain flies or fruit flies?
Drain flies are fuzzy and moth-like, hold their wings roof-shaped, rest on walls near drains and fly in short erratic hops. Fruit flies are tan to brown with often red eyes, hover quickly and gather near fruit and bins. To confirm drain flies, tape a bag loosely over a suspect drain overnight.
Do I need an exterminator for fungus gnats?
Usually not. Fungus gnats breed in damp potting soil, so letting houseplant soil dry further between waterings and emptying standing water from saucers typically resolves it without any product. Professional treatment at $100 to $150 is worth it mainly where the source cannot be found or the problem keeps returning.
Sources
- Contractor-reported price ranges compiled by Angi, HomeGuide and Fixr, 2026. Sample sizes and methods are not published by those sources.
- U.S. Bureau of Labor Statistics, Producer Price Index programme. Confirmed no published series for NAICS 561710.