The presence of small, flying insects in a home can quickly become a major annoyance, leading many people to search for simple household remedies. Among the most popular and persistent of these home remedies is the idea of using common table salt, or sodium chloride, to eliminate the pests. This approach raises a direct question about its viability: is salt an effective solution for killing the tiny flies often generically referred to as “gnats”?
Understanding Common Household Gnats
The term “gnat” is a broad, non-technical label applied to several distinct species of small flies, and the correct elimination strategy depends entirely on identifying the specific pest. Two types are most frequently encountered indoors: Fungus Gnats and Fruit Flies. Fungus gnats (family Sciaridae) are slender, dark-bodied insects with long legs, often found flying near potted houseplants.
These insects breed in the top few inches of moist potting soil, where their larvae feed on organic matter and sometimes plant roots. Fruit flies (family Drosophilidae) are usually tan or brownish with distinctive bright red eyes and a rounder, more compact body shape. Fruit flies hover around fermenting or overripe produce, drains, and garbage cans, as they require sugary, decaying organic material to lay their eggs. A third, less common nuisance is the Drain Fly (or moth fly), a small, fuzzy insect that breeds exclusively in the gelatinous organic slime layer found inside plumbing and drains.
The Science of Salt as a Desiccant
The effectiveness of salt as a pest killer relies on desiccation, the extreme removal of moisture. Salt acts as a desiccant through osmosis, the movement of water across a semi-permeable membrane. When salt crystals or a concentrated salt solution contact soft tissue, they draw water out of the organism’s cells to achieve equilibrium.
This mechanism is highly effective against soft-bodied pests like slugs and snails, which lack a hard, protective outer layer. However, insects—including gnats—possess a rigid outer layer called a cuticle or exoskeleton, covered in a waxy layer. This waxy cuticle is highly water-resistant, making it difficult for external salt to draw out internal moisture effectively. While salt can be toxic if ingested, the primary desiccating effect is largely blocked by the insect’s natural armor.
Is Salt an Effective Gnat Killer?
Despite the simplicity of the method, common salt is impractical and unreliable for controlling a gnat infestation. For adult flying gnats, it is nearly impossible to apply granular salt or a salt solution in a way that causes the necessary level of contact or ingestion to be lethal. Flying insects are too mobile to be effectively coated with a salt solution strong enough to penetrate their cuticle.
Applying a strong salt solution to the soil to kill fungus gnat larvae is also problematic. The sodium chloride can quickly damage or kill the houseplant by interfering with its ability to absorb water and nutrients. Furthermore, the salt crystals are generally not sharp enough to damage the insect’s exoskeleton through abrasion, unlike physical pest controls such as diatomaceous earth. Ultimately, household salt offers no practical solution for eliminating gnats compared to targeted methods.
Proven Methods for Eliminating Gnats
Effective gnat control requires identifying the source and using a targeted approach to break the pest’s reproductive cycle.
Fruit Flies
For fruit flies, the first step is strict sanitation, which involves removing all sources of overripe fruit, cleaning up spills, and regularly emptying garbage cans. Traps can then be set using a small dish of apple cider vinegar mixed with a few drops of liquid dish soap. The vinegar attracts the flies, and the soap breaks the surface tension of the liquid, causing the flies to sink and drown upon landing.
Fungus Gnats
Controlling fungus gnats focuses on the larval stage in the soil. The most important preventative measure is to allow the top layer of potting soil to dry out completely between waterings, eliminating the moist environment the larvae require. For a more aggressive treatment, the soil can be treated with a solution containing Bacillus thuringiensis israelensis (BTI), a naturally occurring bacterium that is harmless to plants and humans. When ingested, BTI releases proteins that are toxic only to the larvae of fungus gnats and mosquitoes, effectively eliminating the next generation of pests.
Drain Flies
Drain flies are best eliminated by physically scrubbing the organic film inside the drainpipe with a stiff brush. This should be followed by the use of an enzymatic drain cleaner to dissolve the remaining breeding material.