Mosquitoes are cold-blooded insects, becoming inactive when temperatures consistently drop below 50°F (10°C). To survive the winter, they employ specialized survival mechanisms known as overwintering. This strategy varies significantly by species and local climate, allowing them to endure low temperatures and a lack of food resources.
The Biological Strategy for Cold Survival
Mosquitoes survive freezing conditions through diapause, a state of suspended development, rather than true hibernation. This hormonally programmed dormancy involves a significant metabolic slowdown, conserving energy. Diapause is triggered in late summer and fall by environmental cues, primarily shorter photoperiods and decreasing temperatures.
In preparation, the mosquito accumulates significant energy reserves, often as fat bodies. The insect also produces specialized compounds called cryoprotectants, which act like biological antifreeze. Glycerol is a common cryoprotectant that lowers the freezing point of internal fluids, protecting cells from ice crystal damage.
This preparation protects the mosquito from lethal cold when external temperatures drop. The non-feeding, non-reproducing state allows the mosquito to remain dormant for several months until spring signals its termination.
Different Overwintering Life Stages
The life stage a mosquito uses to overwinter varies by species, which determines where it seeks shelter. Many floodwater species, such as those in the Aedes genus, overwinter in the egg stage. These eggs are laid on moist soil near the water line and are exceptionally resistant to desiccation and cold.
These dormant eggs remain through winter, hatching only when flooded with water and when the temperature is suitable in the spring. Some species overwinter as larvae, especially in milder temperate zones where water bodies do not freeze solid. These larvae enter a semi-dormant state within the water, remaining suspended until conditions improve.
The most common strategy for many nuisance species, including Culex mosquitoes, is to overwinter as an adult fertilized female. These females mate in the fall and then enter diapause, surviving the winter without needing a blood meal. Males typically die off once the cold weather arrives, leaving the dormant females ready to reproduce the following spring.
Common Winter Hiding Spots
Overwintering mosquitoes seek microclimates that offer stable temperatures above freezing and protection from wind and weather. These locations must be cool enough to sustain the diapause state while avoiding lethal cold. Adult females often shelter in indoor locations that provide a consistent environment, such as basements, crawlspaces, and garages.
Other indoor refuges include utility tunnels, unused sheds, and storm drains, which offer stable temperature and humidity. Outdoor hiding spots must be equally insulated, often involving deep crevices or underground spaces. Natural shelters include hollow logs, beneath tree bark, and within animal burrows or rock crevices.
In aquatic habitats, larvae or eggs may survive in stagnant water that remains liquid beneath a layer of ice. The crucial factor is finding a location where temperature fluctuations are minimal. This stable environment ensures they do not expend limited energy reserves or suffer fatal freezing.