Mosquitoes go through their complex life cycle quickly, typically maturing to adults in a week or two. Adults then live a few weeks to several months more, while they breed and lay eggs to start the next generation.
All mosquitoes begin their life cycle as eggs, laid either on or near water. The eggs are tiny, less than a millimeter long. They begin white, but darken to black, brown or reddish brown within the first day.
Some species lay their eggs connected together in rafts which rest on the surface of the water, while others lay the eggs so they float individually. These eggs hatch within a few days after they're laid, but other mosquitoes, typically of the Aedes genus, lay eggs on the soil near water, rather than on the water itself. Their eggs can survive long periods of drought or cold, before rain or snow-melt comes and washes them into water or raises water levels to where they are. Aedes eggs may require certain conditions before they'll hatch, such as a certain day length, a period of freezing, or being wetted and dried several times. This prevents them from hatching in midwinter or too soon in spring, before conditions are right. These kinds of eggs can be transported hundreds of miles before they hatch, and in fact, that's how the Asian tiger mosquito came to the United States from the other side of the globe.
Once any kind of mosquito eggs hatch, they producing the next stage in the life cycle, the larva (plural "larvae"). They're commonly called wrigglers or wigglers, because they move in the water by wriggling. You can see them swimming or hanging close to the surface in rain barrels, flooded ditches, the edges of swamps or other stagnant water. They live in water but breath air, so like snorkelers, they have a breathing tube and must come close to the surface often to get oxygen. When resting, they usually hang down from the surface or, in some species, lie horizontally just below it.
The larvae eat tiny organic particles in the water. A few of the larger species, like those of the Toxorhynchites genus, eat smaller creatures, including other mosquito larvae. While the larvae feed, they grow, and as they get larger, they shed their skin. Each stage in between shedding is called an "instar," and by the fourth instar, the larvae are ready to go on to the next stage in their life cycle, the pupa (plural "pupae"). The larvae typically go from egg to pupa in less than a week, though some take a week or more.
Almost Done: Pupae
Just as caterpillars emerge from coccoons to fly away as butterflies, the little wrigglers go into a pupal stage so they can eventually fly away as mosquitoes. The pupae still live in the water and move around, though they look different. The larvae are generally long and straight, while the pupae are comma-shaped, with a larger section that contains the mosquito's head and front part of its body. The thinner curved section has paddles at the end which allow it to swim, though it doesn't eat during this stage. It still needs to come to the surface to breathe through tubes on its head.
The pupal stage may last a few days, after which the adult mosquito emerges from the top of the pupa up into the air, for the final stage in the life cycle. A few species, though, spend the winter in their underwater stages and don't emerge to fly away as adults until the next spring.
Both male and female adults look similar at a distance. Both buzz, though only the female bites. With a magnifying glass, you can see that the mouth parts of the female are uniquely adapted to be able to bite animals, as well as to feed on nectar and similar plant products, which are the usual food of both males and females.
After maturing for three to five days, the adults mate. The male dies within a week or so, but the female may live several weeks or even months, if she belongs to one of the species which hibernate over the winter as adults. After she mates, she needs to find an animal to get a meal of blood, to make the eggs grow within her. Though each female mates only once, she may lay several sets of eggs during her lifetime.
Different species prefer different hosts. Some will bite either humans, animals or birds, while others prefer one type, and a few choose cold-blooded animals. A small number of species don't need blood at all, though most do.
After drinking her fill of blood, either in one bite or several, the female finds a sheltered place to rest for several days until her eggs are fully grown inside her. At that point, she will look for a location to lay the eggs, either on water or near it, depending on her species.
After laying, she'll look for another creature to bite, so she can grow another batch of eggs, but she won't need to mate again. Females may not survive long enough to lay one batch of eggs, or they may lay only one, or they may survive to lay several during one summer. At the end of summer, the female will either die or, if she belongs to a species that hibernates, will spend the winter hibernating with fertile eggs inside her, waiting to lay them in the spring.
Public domain photos courtesy of the CDC .