Los Angeles County West Vector & Vector-Borne Disease Control District

Mosquito Ecology

What is a Mosquito?

    Any winged insect of the family Culicidae, order Diptera, having a narrow abdomen, a long and slender proboscis, and narrow wing scales on the wing margins and veins. 
    Males have feather-like antennae and mouthparts which are not adapted for piercing.   Females have slender antennae and a set of needlelike organs in the proboscis with which they puncture the skin of animals to feed on their blood.

    In some species (Aedes spp.), eggs are laid directly on or into soils that will later be flooded.  Other species lay their eggs directly on the water either singularly (Anopholes spp.) or in egg rafts(Culex spp.).  The larvae, sometimes called wigglers because of their swimming motions, are aquatic, but usually come to the surface to breathe.  The pupae, sometimes called tumblers because of their swimming motions, are also aquatic and generally found at the water surface.   Many species pass through several generations a year and hibernate through the winter as adults; others overwinter in the egg or mature larval stage.  Some mosquitoes are important in the transmission of disease-causing agents, whereas others are important more for their pestiferous habits.

  Mosquitoes must have water to complete their life cycle.                               

  Only seven days are required to complete their life cycle (egg to adult) during warm weather.

  Mosquitoes do not develop in grass or shrubbery, although flying adults frequently rest in these areas during daylight hours.

  Only the female mosquito bites to obtain a blood meal.  The male mosquito lives only on plant juices.

  The female may live as long as three weeks during the summer or many months over the winter in order to lay her eggs in the following spring.

The Mosquito Life Cycle

    The most common mosquitoes lay egg rafts that float on the water.  Each raft contains from 100 to 400 eggs.  Some mosquitoes lay their eggs singularly on the water surface, and some lay their eggs on rocks and vegetation awaiting to be submerged by a strong rain.  Within a few days of being laid or submerged by water, the eggs hatch into larvae.

    The larva or "wiggler" comes to the surface to breathe through a tube called a siphon.  It molts (sheds its skin) four times during the next several days.   These molts are called instars.  It grows rapidly between each molt.   After the fourth instar it changes into a pupa.



    The pupa or "tumbler" cannot eat.  It breathes through two tubes on its back called trumpets.  The adult mosquito grows inside the pupa and in two days or so, when it is fully developed, it splits the pupal skin and emerges as an adult mosquito.



The newly emerged adult rests on the surface of the water until it is strong enough to fly away and feed.


Common Mosquitoes Found in Los Angeles County


Culex tarsalis (CT) -  Western Encephalitis Mosquito. Primary vector of WNV, SLE and WEE in California.


Culex quinquefasciatus
- Southern House Mosquito. WNV, SLE, and WEE vector. 


Culex erythrothorax (CE) - Tule or Cattail Mosquito. WNV, SLE, and WEE vector. 



Culex stigmatosoma (CS) - Banded Foul-water Mosquito. May act as enzootic amplifiers of SLE and WNV in nature.



Culiseta incidens (CI) - Cool-weather Mosquito. WNV vector.



Culiseta inornata (CA) - Large Winter Mosquito. WNV and WEE vector.





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