Mosquitoes are cold-blooded insects, meaning their internal body temperature is regulated by the external environment. This makes temperature the most significant factor limiting their activity, growth, and geographic spread. The temperature required to kill a mosquito depends on the specific life stage and the species involved. Their ability to persist through the winter relies on biological strategies that either resist acute cold or allow for a state of suspended animation.
Immediate Lethality: Adult Mosquitoes and Freezing Temperatures
For the active adult mosquito, temperatures near or below freezing are immediately life-threatening. Since they cannot internally generate heat, their metabolic processes slow drastically as the air cools. Below 50°F (10°C), most adult mosquitoes become sluggish, unable to fly, feed, or mate.
The point of death for an exposed adult is reached when the air temperature drops below 32°F (0°C). At this temperature, the water inside the mosquito’s body begins to freeze, leading to ice crystals that rupture cells and cause fatal damage. The duration of exposure is a determining factor, as even a short burst of cold may not be lethal if the insect finds shelter. For most species, two consecutive hours below 28°F (-2.2°C)—often termed a “killing frost”—is sufficient to eliminate nearly all exposed adult populations.
Surviving the Winter: Biological Mechanisms of Diapause
While a single hard freeze is lethal to active adults, many mosquito species survive cold for months using diapause. This survival strategy is a state of arrested development, triggered in the late summer or early fall not by freezing temperatures, but by environmental cues like shortening daylight hours.
The female mosquitoes that enter diapause, such as the common house mosquito (Culex pipiens), cease blood-feeding and consume plant sugars to build up fat reserves. They also produce cryoprotectant compounds like glycerol, which act as a biological antifreeze. Glycerol lowers the freezing point of their internal fluids, preventing lethal ice crystal formation within their cells during cold periods.
These diapausing females seek sheltered, stable locations for the winter, often in protected microclimates. These overwintering sites include basements, cellars, storm drains, culverts, and hollow logs, where the temperature remains consistently cool but generally stays above freezing. The mosquito’s metabolic rate slows significantly, allowing the female to survive without food or water until spring returns.
The Resilience of Eggs and Larvae
Many temperate species utilize their immature life stages to persist through the cold, rather than surviving as adults. Species belonging to the Aedes genus, such as the Asian tiger mosquito (Aedes albopictus) and yellow fever mosquito (Aedes aegypti), rely on their eggs for overwintering. These container-breeding eggs are highly desiccation-resistant and are laid just above the waterline in dried containers, tires, or tree holes during the fall.
These eggs are remarkably freeze-tolerant, a characteristic known as cold hardiness. Experiments show that Asian tiger mosquito eggs can survive short exposures to temperatures as low as -10°C. Even the tropical yellow fever mosquito’s eggs can withstand -2°C for several days, allowing them to spread into regions previously thought too cold. The dormant embryo waits for the right combination of moisture and warm temperature in the spring to trigger hatching.
Mosquito larvae, often called wigglers, are much more susceptible to freezing temperatures than the eggs. Larvae cannot survive if the water they inhabit freezes solid. However, the water itself provides insulation, especially in larger bodies. Larvae can often survive under a cap of ice in a container or pond, provided the water beneath remains liquid and above their lethal temperature threshold, which can be around 46°F (7.8°C) for some species.