The term “gnat” is a general label for small, non-mosquito flies that swarm, typically referring to two distinct types of insects when seen around a lawn. These flying pests are not living directly on the grass blades, but their presence indicates that the underlying soil and environmental conditions are highly favorable to their life cycle. Understanding the specific type of insect and the cause of the attraction is the first step toward effectively managing their population in your yard.
Identifying the Small Flying Insects Near Grass
The insects hovering over your lawn are typically either Fungus Gnats or Biting Midges, often called No-See-Ums, and knowing the difference is important. Fungus gnats (Sciaridae family) are the most common type of “lawn gnat,” appearing as dark, delicate-looking flies that are about one-eighth to one-quarter inch long. These weak fliers do not bite humans or pets, and you will usually see them fluttering low to the ground or running across the soil surface.
Biting Midges (Ceratopogonidae family), by contrast, are much smaller, measuring only about one-sixteenth of an inch, which is why they are frequently called No-See-Ums. The female midges have piercing-sucking mouthparts and will bite warm-blooded animals in search of a blood meal, leaving behind small, painful, and intensely itchy welts. While both insects are attracted to moist conditions, the presence of bites is the clearest distinction for the average person trying to identify the pest.
The Environments That Attract Gnats Near Grass
Gnats are not attracted to the grass itself but to the conditions of the soil and the organic matter beneath the turf. These insects require a consistently moist environment for their larvae to develop. Overwatering is a frequent cause, as saturated soil maintains the high moisture levels that Fungus Gnat females seek out to lay their eggs.
The larvae of fungus gnats feed on fungi, decaying organic matter, and algae within the top one to three inches of the soil profile. A thick layer of thatch—the build-up of dead grass stems and roots above the soil—creates an ideal, moisture-retaining, organic-rich habitat for them.
Poor drainage, heavy clay soils, and low-lying areas where water tends to pool also create saturated conditions that allow gnat populations to flourish. Decaying materials like fallen leaves, grass clippings, and certain mulches provide a rich source of food and a protected, damp nursery for the larvae.
Strategies for Reducing Gnat Populations in Lawn Areas
Reducing gnat populations requires altering the environmental factors that enable them to breed. Since excessive moisture is the root cause, adjusting your irrigation schedule is the most important step. Allow the top layer of soil to dry out completely between watering sessions instead of applying light, frequent waterings.
Improving the soil’s ability to drain water will also make the area less hospitable to the larvae. This can be accomplished by aerating the lawn to reduce soil compaction and by removing excessive thatch. Regularly clearing away all decaying organic debris, such as grass clippings and fallen leaves, eliminates a significant food source and breeding ground for the pests. For high-density infestations, a biological control like the soil-applied bacterium Bacillus thuringiensis subspecies israelensis (Bti) can be used. Bti is specifically toxic to gnat larvae without harming plants, people, or pets.