Gnats are small, winged insects, often fungus gnats, that commonly infest indoor environments like houseplants or drains. Their presence can be bothersome due to their numbers and persistent flying.
Gnat Vulnerability to Temperature Extremes
Extreme temperatures significantly impact the survival of gnats across all their life stages. High temperatures denature proteins and disrupt metabolic processes within the insect’s cells, leading to death. Conversely, very low temperatures cause ice crystal formation within tissues, damaging cell structures and ultimately proving lethal. The specific temperature thresholds vary slightly depending on the gnat species and its developmental stage.
For fungus gnats, eggs are eliminated above 115°F (46.1°C). Larvae, found in moist soil, die when temperatures exceed 125°F (51.7°C). Adult gnats succumb to temperatures above 135°F (57.2°C). Sustained exposure to these temperatures is important for effective eradication.
While high temperatures are broadly lethal, gnats exhibit varying degrees of cold tolerance. Some fungus gnat species, like Exechia nugatoria, demonstrate remarkable resilience, with some individuals surviving temperatures as low as -25 degrees Fahrenheit (-31.5 degrees Celsius). However, complete mortality for this hardy species occurs around -50.7 degrees Celsius (-59.3 degrees Fahrenheit). In general, outdoor gnat populations naturally decrease when temperatures fall below 44.6 degrees Fahrenheit (7 degrees Celsius), with temperatures in the teens likely eliminating them.
Utilizing High Temperatures for Gnat Control
Applying high temperatures offers an effective approach to gnat control, particularly for infestations in soil or drains. Boiling water, which reaches 212 degrees Fahrenheit (100 degrees Celsius), is a straightforward method. Pouring boiling water down household drains can eliminate drain gnats, their eggs, and larvae by washing away the organic matter they feed on. This method is best used cautiously to avoid damage to plumbing.
For gnats infesting potted plant soil, heat treatment targets eggs and larvae. Baking potting soil at 350°F (176.7°C) for 30 minutes sterilizes it before planting. Steaming potting mix at over 150°F (65.6°C) for at least 30 minutes also kills gnat eggs and larvae.
For existing plant infestations, less extreme heat can be applied with care. A clothes iron used with steam can deliver heat to the top half-inch of soil, where gnat larvae often reside, without harming the plant’s deeper roots. Solarizing soil, by moistening it and placing it in a clear or black plastic bag in a sunny location for four to six weeks, can also raise temperatures sufficiently to kill pests. These methods provide practical, non-chemical options for reducing gnat populations.
Applying Low Temperatures for Gnat Control
Utilizing low temperatures, particularly freezing, can also be a viable option for eliminating gnats, especially in items that can withstand cold. Placing infested potting soil, without the plant, into a freezer can kill gnat larvae and eggs if the soil completely freezes. This approach ensures that the cold penetrates thoroughly, halting the gnat’s life cycle. Freezing seed starting mixes for at least 48 hours is also suggested to prevent gnat outbreaks.
However, the effectiveness of freezing can depend on the specific gnat species and the duration of exposure. While some gnat species are highly susceptible to cold, others possess remarkable adaptations for surviving sub-zero temperatures. Therefore, simply placing an infested potted plant outside during winter may not guarantee complete eradication, as some eggs or dormant larvae could survive and hatch when warmer conditions return. For practical household control, freezing is generally most effective for detached soil or items that can be thoroughly chilled for an extended period.