The mosquitoes are a family of small, midge-like flies. Like all flies, mosquitoes go through four stages in their life – egg, larva, pupa, and adult. We call this as the life cycle. Each of these stages is morphologically different from the other, with even the habitat of each stage differing. The first three stages – egg, larva and pupa are largely aquatic, whereas the adult stage is aerial. The eggs are laid one at a time and they float on the surface of the water. Most eggs hatch into larvae within 48 hours. Mosquito larvae live in water from 7 to 14 days depending on the water temperature. After the larvae have completed moulting, they become pupae. After a few days or longer, depending on the temperature and other circumstances, the pupa rises to the water surface, the dorsal surface of its cephalothorax splits, and the adult mosquito emerges. The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and harden its parts. Also, the wings have to spread out and dry properly before it can fly.
This video describes the life cycle of a mosquito.