Adult mosquitoes' lifespans vary from a few days to several months, depending on the species. Some mosquitoes live only in the summer and die when cold weather comes, but their eggs survive the winter and hatch in spring. Others hibernate during the winter as adults, so their lifespan as full-grown mosquitoes lasts for months, continuing into the following year.
Mosquitoes that spend the winter as eggs develop into adults within two weeks after hatching in the spring. The adult males survive on nectar and similar foods, since they don't need the nutrition that comes from blood, like females do. The males live only about a week, long enough to swarm and mate with the females. The females' lifespan is longer, up to a month or two, though many die sooner, eaten by preditors, blown around by storms or slapped as they're trying to get a drink of blood to help them develop their eggs. In nature, birds, dragonflies and spiders eat them, and of course humans do their best to get rid of them in various ways besides killing them directly. One of the most satisfying ways to see a painful, whining mosquito meet its end, when it tries to interrupt your peaceful summer afternoon, has got to be with a swatter like this.
Thanks to the efforts of preditors and humans, only a small percentage of adult mosquitoes survive for their full potential lifespans, but one female still may lay hundreds of eggs, even if she can survive only long enough to bite something and lay one batch.
Females require the nutrients in human or animal blood to nourish their eggs, so they bite a person or animal, rest for a few days while their eggs are growing inside them, lay the eggs, and repeat the process as long as they live. If they belong to a species which hibernates during the winter, they seek a sheltered location when the weather turns cold and go into hibernation with fertilized eggs inside them, waiting to emerge in spring. If they're the kind of mosquito which dies off when cold weather comes, they lay eggs which lie on the ground over the winter and hatch when warm weather returns in spring.
When we talk about the lifespan of mosquitoes, we usually think of the time that they're flying around as adults, but their full lifespan includes the time they spend in water as larvae also, and one might even count the time they're only eggs waiting to hatch. Most mosquitoes develop into adults quickly after the larvae hatch, so the time that they spend as larvae adds only a couple of weeks, sometimes as little as one week. A few rare ones, though, spend months as larvae. The unusual pitcher plant mosquito, Wyeomyia smithii, spends the winter as a larva in the small puddle of water held within the cup-shaped leaves of the pitcher plant. Even though the water freezes, the larvae survive and go on to develop into adults the next spring. Other species hibernate as larvae, but they dive to the bottom of ponds, where the water never freezes, and become dormant there until warm weather returns.
Scientists care about the lifespan of Anopheles mosquitoes, because they spread malaria, especially in Africa. The parasite which causes malaria must develop for 10 days to three weeks inside the mosquito, before the next bite will infect another person. If the mosquito dies sooner than that, it can't spread malaria. Scientists estimate that fewer than 1 in 10 malaria mosquitoes survive long enough to spread the disease, but that's still too many, so they hope to shorten malaria mosquitoes' lifespan even more. For more information on the life of malaria mosquitoes, see this article.
The Culex mosquitoes that carry the West Nile virus in the United States also must live 5 to 15 days after biting a virus-infected bird before they can pass the virus on to a human. Since some Culex mosquitoes species survive over the winter as adults, scientists have been collecting and testing them during the hibernation, and discovered signs that the virus may be able to survive in them over the winter, though they believe the risk posed to humans is low.
Larva photo by Rkitko, Wikimedia Commons.