• Long, slim, narrow body
  • Long, narrow wings
  • 3 pairs of legs
  • Antennas
  • A proboscis (in females) for sucking blood


  • Mosquitoes can transfer and transmit diseases, such as West Nile virus, to humans and they can cause sickness or sometimes even death
  • Can cause extreme itchiness and other possibly severe reactions
  • Causes nuisance problems for rural home owners
  • Interferes with outdoor activities and sports


  • Carbon dioxide from the breaths of humans and animals
  • Body odors such as sweat and lactic acid, combined with heat
  • Moisture on skin can be a potential blood feed for them
  • Standing water makes a perfect breeding ground
  • Attracted to dark colors on clothes
  • Movement from the changes in light around the moving object


  • Get rid of or change accumulated water in areas that collect them
  • Avoid going out around dusk to dawn
  • Wear protective clothing  (e.g. long sleeves, long pants)  when in areas where mosquito activity is high
  • Use insect repellents on the skin
  • Treat clothing and outdoor gear with insecticide or insect repellents


  • Do not scratch bitten area
  • Clean the bite area with plain water, rubbing alcohol, or alcohol wipes
  • Apply an ice pack or ice cubes to the bites
  • Apply anti-itch or itch-soothing creams


Life Cycle of a mosquito: Egg, larva, pupa, adult

(Stages are all aquatic until adult)

  • The Egg Stage
    • Most mosquito species lay their eggs on the surface of water, but the some (Aedes) mosquitoes lay their eggs on damp soil on the surface of water.
    • Depending on the species of the mosquito, eggs are either stuck together in rafts containing hundreds of eggs or they are laid individually. 
    • It takes about 48 hours for most eggs to hatch in the larvae stage, depending on environmental conditions and species' types.
  • The Larva Stage
    • Mosquito larvae are aquatic surface breathers.
    • Most larvae, except the Anopheles, hang from the water's surface for oxygen and they have siphon (tubes for breathing).
    • Anopheles' larvae must lie parallel to the water's surface and they receive oxygen supply through spiracles (an opening used for oxygen).
    • Larvae go through 4 instars, which are stages between molts. With every molt, they shed their skin and become larger in size while they feed on organic matter and other microorganisms.
    • The fourth and final instar that the larva reaches is where it enters the pupa stage.
  • The Pupa Stage
    • A resting, non-feeding stage where mosquito pupa evolve into an adult.
    • It takes about 2 days until the adult is fully developed.
    • When development is complete, the pupa skin will split as the mosquito emerges as an adult.
  • The Adult Stage
    • The newly emerged mosquito will rest on the water's surface.
    • The mosquito dries and solidifies its body parts before it is ready to take flight.  

Species of Mosquitoes found in California

Culex quinquefasciatus

(Southern House Mosquito) – This is a brown, medium-sized mosquito with unbanded legs.  This mosquito peaks in the summer and fall but can also be seen year round.  They readily enter homes and bite indoors during the nighttime.  The quinquefasciatus primarily feeds on birds and will feed on mammals as a second choice.  It lies its larval in warm, sheltered, polluted (or foul) water, such as waste treatment ponds, neglected swimming pools, cesspools, septic tanks, fishponds, and catch basins.  In California, this mosquito species has tested positive for: Western Equine Encephalitis (WEE), St. Louis Encephalitis (SLE), and West Nile Virus (WNv).  The Culex quinquefasciatus may be the prime vector for West Nile virus in urban areas as well as a probable vector of dog heartworm disease.

Culex tarsalis

(Western Encephalitis Mosquito) – A brown, medium-sized mosquito that is capable of flying long distances, approximately 16+ miles or 20-25 miles with wind assistance.  This is important for the transmission and distribution of the encephalitis viruses.  Their physical features include: a white band on the proboscis that does the blood-sucking, V's on their abdomen, and banded black and white legs.  The tarsalis is active during the spring and fall time where it lays its eggs in various places from clean to partially foul water.  They generally use rain pools, decorative ponds, and irrigation water as their breeding zone.  Both the male and female mosquitoes are attracted to light traps and they are highly attracted to CO2 baited traps.  This mosquito primarily feeds off birds, but they will readily attack humans at night if they are disturbed.  The Culex tarsalis is the primary vector of West Nile virus (WNv), Western Equine Encephalomyelitis (WEE), and St. Louis Encephalitis (SLE).  

Culex stigmatosoma

(Foul Water Mosquito) – This medium-sized, brown mosquito has ovals on its abdomen and black and white striations on its legs.  It is commonly referred to as a "foul water" mosquito because of its association with polluted water.  This mosquito's larval habitat can be in either natural or man-made, polluted waters such as dairy ponds or sewage treatment facilities.  When an adult, the stigmatosoma actively peaks in the summer months and they feed primarily on birds as they rarely bite humans.  This species occasionally creates domestic, industrial, and agricultural pest problems.  The Western Equine Encephalitis (WEE) has been associated with this mosquito; however, the Culex stigmatosoma efficiency towards WEE carriers has been reduced due to their reluctance in biting humans.  They have also been identified as a carrier of West Nile virus.

Culex erythrothorax

(Tule Mosquito) – This is a medium-sized, reddish-orange mosquito wirth unbanded, brown legs.  This species breeds in tule marshes that are thick with vegetation.  The larvae can survive throughout the winter and emerge as adults in June through October.  This is an opportunistic and aggressive mosquito that will bite during the day if disturbed, as well as during dusk and dawn.  The erthrothorax feeds off birds and humans and is capable of reaching high numbers.  This mosquito species is rarely a public nuisance because it does not venture far from its breeding grounds; however, those who reside near wetlands, where these insects breed, find this mosquito to be a huge pest.  The Culex erthrothorax has the ability to transmit Western Equine Encephalomyelitis (WEE), St. Louis Encephalitis (SLE), and West Nile virus (WNv).

Culesita incidens

(Cold Weather Mosquito) – This large mosquito has slender white bands on the tarsi, or part of its lower leg, and dark patches on its wings.  They can be seen throughout California, but mostly in the mountain, coastal, and foothill regions where the summers are hot and the winters are cold.  The incidens mainly breed during the fall, spring, and winter seasons while remaining dormant during the summer months.  They prefer to breed in clean, cool water that has some shade, for example, rock pools, melted snow, and hoof prints.  In some areas, this mosquito is considered a pest to humans, but the Culiseta incidens prefers to feed off large mammals, such as livestock, and it is not considered a vector for human disease.

Culesita inornata

(Large Winter Mosquito) – This is a large, rusty-brown mosquito with no noticeable markings on its wings and has unbanded legs, also known as the tarsi.  They have been observed all throughout California.  This cool weather mosquito is prevalent during the fall and springtime.  It is also speculated to be active in the winter months going into its dormant mode in the summer.  In the sierras, this species breeds in fall, summer, and spring while aestivating in the harsh winters.  Their eggs are laid in standing water as well as moderate organic pollution.  Culiseta inorata adults are strongly attracted to light sources.  The females frequently feed at dusk on livestock and sometimes on humans.  When large populations of this species exist, it can cause economic loss through livestock distress.  This mosquito species is not considered a vector of human disease; however, in California, they have been found infected with the Jamestown Canyon virus (JC).

Anopheles hermsi

(Southern California Malaria Mosquito) – This species is medium-sized, slender and brown in color with unbanded legs.  Their larvae can be found in several different habitats: willow trees, cattail, river margins, river edges, pools, and canyon springs.  The genera distribution of this mosquito appears to be limited to the coastal regions that are south of San Luis Obispo, occasionally south and west of Tehachapi Mountains, and some isolated cases in the northern coastal regions.  In San Diego County, the Anopheles hermsi rarely appears throughout the year with peak activity in June and July.  They are flighty, aggressive biters with peak activity ½ an hour, or more, before and after sunrise and sunset.  These mosquitoes attempt to obtain blood meal on a variety of different hosts, such as goats, chickens, dogs, cattle, and humans.  In San Diego County, Anopheles hermsi has recently been implicated as the vector in locally transmitted human malaria outbreaks.

Aedes sierrensis

(Western Tree-Hole Mosquito) – These adult mosquitoes have contrasting black bodies with white scales, black and white banded tarsi, unbanded proboscis (elongated appendage from its head), and the palpi tips (appendage attached to the mouth, serving as a sense organ) are white.  They are most prevalent in the woodlands and coastal regions of the Sierra Nevada foothill communities in northern California, but are also found  throughout the state.  This mosquito has limited flight range and stays within its breeding sites.  Their larvae can occur in the same habitat as other mosquito species and they usually have extremely long anal papillae, or gills.  The larvae and eggs can be found in rotten tree holes of many different tree species that have developed a small, external cavity.  Sometimes, their larvae can also be discovered in old tires, water barrels, leaf litter, and tubs.  Adult Aedes sierrensis activity peaks in the early springtime where they get their blood meals primarily from rodents, and small and large mammals (including humans) in the day, at night, and around dusk.  They are not considered a vector of human disease, but have been implicated as the most important vector of dog heartworm disease in northern California. 


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Deep Look by PBS Science