Mosquito Biology

Two types of mosquitoes plague Illinois – floodwater and vector mosquitoes.

About Floodwater Mosquitoes

Floodwater mosquitoes lay their eggs in low-lying areas that will eventually become inundated with water. The most common of these is the Aedes vexans, known as a vicious biter that is most active between dusk and dawn, but can be aggressive daytime biters when disturbed from their resting areas in and around foliage.

Floodwater Mosquito Facts

  • They are the most common type of mosquito
  • They are found mostly in or near heavily forested areas of the district
  • Floodwater mosquitoes are not known to be transmitters West Nile virus in this area

About Vector Mosquitoes

Vector mosquitoes typically lay their eggs directly on stagnant water. They lay their eggs in anything that holds water, even a bottle cap. We call them container breeders. The Culex pipiens and Aedes trisiriatus are among the vector mosquitoes found in Illinois. Culex pipiens are the primary carriers of the West Nile virus and are more abundant during hot and dry periods. Aedes trisiriatus are the main carriers of La Crosse encephalitis.

Vector Mosquito Facts

  • Vector mosquitoes are known to carry diseases
  • Culex pipiens mosquitoes are the predominant carriers of West Nile virus
  • Aedes trisiriatus are the main carriers of LaCrosse encephalitis

The Mosquito Life Cycle


The Egg Stage

Adult female mosquitoes lay mosquito eggs. The eggs are laid:

  1. Singly on the water surface – Anopheles, the malaria mosquito
  2. Singly above the water line – Aedes, the floodwater mosquito
  3. In groups, known as egg rafts, on the waters’ surface – Culex, the house mosquito

The floodwater mosquito species can survive the winter as eggs, while Culex can overwinter as adults.

The Larval Stage

Mosquito larvae, known as wrigglers, must develop in standing water, but they breathe through an air tube at the rear of their bodies. Larvae feed on detritus and microorganisms. They undergo four stages of development called instars. Between each instar, the larvae feed, shed their skin and become larger. During the warm days of summer, larvae can complete development in five to seven days.

Development Facts

  • Anopheles larvae develop in permanent ponds and marshes
  • Aedes larvae develop in temporary woodland pools and intermittently flooded ditches
  • Culex larvae are found in catch basins and other natural and artificial containers; Culex prefer water that is stagnant or has a lot of organic material

The Pupal Stage

After completing the fourth instar, larvae shed their skin and become pupae. During the pupal stage, the mosquito undergoes final development into an adult. Pupae, like larvae, breathe air but do not feed. After two to four days, the skin of the pupae splits and the adult mosquito emerges on the surface of the water.

The Adult

After 15 to 20 minutes, the adult mosquito is ready for flight. Both males and females feed on plant nectar that is used for flight energy. Only the female mosquito takes blood meals. Males can’t bite because they don’t posses the specialized mouth parts required to do so. The female uses the protein found in red blood cells to manufacture eggs.

Generally, most adult mosquitoes do not fly further than one to four miles from where they emerge, but some species such as Aedes vexans can fly 20 miles if weather conditions are right.