Gnats are tiny, winged insects, generally small flies belonging to the order Diptera, often seen hovering near houseplants or fruit. The gnats most people notice are typically fungus gnats (families Sciaridae and Mycetophilidae), which are attracted to moist soil and decaying organic matter. These insects thrive in warm conditions, with optimal temperatures ranging from 70 to 80 degrees Fahrenheit. Like many other insects, however, gnats have developed physiological and behavioral mechanisms to survive periods when temperatures drop below this preferred range.
Identifying Common Gnat Types
The way gnats respond to cold depends on the specific species and environment, broadly separating them into outdoor and indoor populations. Outdoor gnats, such as biting midges, are exposed directly to winter conditions and must rely on biological survival strategies. These species usually enter a state of developmental arrest to survive seasonal temperature shifts, often overwintering as eggs or larvae buried in the soil or mud.
Indoor populations, primarily fungus gnats, face environmental conditions buffered from the outside climate. Since houseplant soil, plumbing, and decaying organic materials provide a constant source of moisture and food, the ambient indoor temperature becomes the primary factor for their activity. An indoor environment above 68 degrees Fahrenheit allows fungus gnats to maintain continuous, year-round breeding cycles, bypassing the need for a cold-survival mechanism. This explains why people see active gnats indoors even during winter.
The Cold Weather Response: Dormancy and Diapause
When outdoor temperatures fall consistently, gnats must employ a survival strategy, which involves either simple dormancy or a deeper process called diapause. Simple dormancy, or quiescence, is a direct, immediate response where the insect becomes inactive due to the cold, but it can quickly resume development if the temperature rises. Diapause, conversely, is a genetically programmed, hormonally-driven state of developmental suspension that is triggered by predictive cues, such as the decreasing photoperiod (day length) in late summer or early fall.
Entering diapause requires the gnat larva to undergo metabolic restructuring well before the onset of freezing weather. The insect slows its metabolic rate to conserve energy, and it begins to reduce the water content within its body. This water reduction is coupled with the production of cryoprotectants, which are antifreeze-like compounds such as glycerol and sorbitol. These polyols lower the freezing point of the gnat’s internal fluids and prevent lethal ice crystal formation, allowing them to tolerate temperatures that would otherwise be fatal.
The physiological complexity of this adaptation is demonstrated by certain arctic fungus gnat species, which exhibit a rare ability to be simultaneously freeze-avoiding and freeze-tolerant. Some parts of their body, particularly the head and thorax, are protected from freezing by noncolligative antifreeze proteins. Meanwhile, the gnat’s abdomen is allowed to freeze at a controlled, specific temperature, an adaptation that might help conserve body moisture over the long winter.
Lethal Temperature Limits and Shelter
For most common gnat species, the lethal temperature zone begins slightly below the freezing point of water, though the exact threshold varies depending on the life stage. Adult gnats are the most vulnerable, and sustained exposure to temperatures below 32 degrees Fahrenheit will kill them within a short period. The eggs, larvae, and pupae, however, are more cold-tolerant, particularly when they are in diapause and protected by cryoprotectants.
This tolerance is further enhanced by the insulated microclimates where gnat larvae reside. Outdoor gnat eggs and larvae overwinter deep within the soil or beneath leaf litter, where ground temperatures remain warmer and more stable than the air temperature. Even during a cold snap where the air temperature drops to 10 degrees Fahrenheit, the soil a few inches below the surface may hover near or just above freezing. For indoor fungus gnats, the moist soil of a potted plant acts as a thermal buffer, and the warmth of a home ensures that the larvae never face a temperature low enough to trigger mortality.
The Seasonal Cycle of Gnat Activity
The visible seasonal cycle of gnat activity outdoors results from the adult population dying off when temperatures drop below their tolerance range. In autumn, as days shorten and the weather turns cold, adult gnats disappear because they cannot survive the conditions or sustain flight. What remains are the overwintering life stages—cold-hardy larvae or eggs that have entered diapause within the protected soil.
The life cycle resumes in the spring when rising soil temperatures and increasing moisture levels signal the end of diapause. Once the ground warms, the larvae complete their development, pupate, and emerge as flying adults, initiating a new breeding cycle. This seasonal pattern is largely irrelevant for indoor gnat populations, which are sustained by the constant, favorable conditions of a home, allowing reproduction continuously without the need for a cold-induced developmental pause.