In most female mosquitoes the mouth parts form a long proboscis for piercing the skin of mammals (or in some cases birds or even reptiles and amphibians) to suck their blood. The females require protein for egg development, and since the normal mosquito diet consists of nectar and fruit juice, which has no protein, most must drink blood to get the necessary protein. Males differ from females, with mouth parts not suitable for blood sucking. Oddly females of one genus of mosquitoes, Toxorhynchites, never drinks blood. The larvae of the large mosquito are predatory on other mosquito larvae.
The mosquito goes through four distinct stages in its life cycle: egg, larva, pupa, and adult. The length of the first three stages is species- and temperature-dependent. Culex tarsalis may complete its life cycle in 14 days at 20 °C and only ten days at 25 °C. Some species have a life cycle of as little as four days or up to one month. The larvae are the "wigglers" found in puddles or water-filled containers. These breathe atmospheric oxygen through a siphon at the tail end. The pupae are nearly as active as the larvae, but breathe through thoracic "horns" attached to the thoracic spiracles. Most larvae feed on microorganisms, but a few are predatory on other mosquito larvae. Some mosquito larvae, such as those of Wyeomyia live in unusual situations. These mosquito wigglers live either in the water collected in epiphytic bromiliads or inside water stored in carnivorous pitcher plants. Larvae of the genus Deinocerites live in crab holes along the edge of the ocean.
Much of modern mosquito control is no longer dependant on dangerous pesticides but specialized organisms that eat mosquitos, or infect them with a disease that kills them. Such methods can even be used in Conservation Areas, like the "Forsyth refuge" and the Seaview Marriott Golf Resort, where some major mosquito control is performed and monitored using "killifish" and juvenile eels. The success is documented with most advanced underwater microscopes like the ecoSCOPE. However, outbreaks of human mosquito-borne diseases may still result in fogging with chemicals that are less toxic than those used in the past.
Dragonflies, also known as mosquito hawks, are excellent control agents. Dragonfly nyads consume mosquito larvae in the breeding waters, and adult dragonflies eat adult mosquitoes, particularly the day flying Asian tiger mosquitoes. Fogging for adult mosquitoes can backfire and increase long term populations if it removes dragonflies and other natural controls.
Some mosquitoes are capable of transmitting protozoan diseases such as malaria, filarial diseases like filariasis, and viral diseases such as yellow fever, dengue, encephalitis, and West Nile virus. West Nile Virus was accidentally introduced into the United States in 1999 and by 2003 had spread to almost every state.