This species is most commonly found breeding in high organic content water sources such as winery waste, sewage, log, and dairy ponds. Adult females prefer to feed on birds but will also bite humans.

The Foul Water Mosquito (Culex stigmatosoma) is one of 53 types of mosquitoes that occur in California. Culex stigmatosomais known as the Banded Foul Water Mosquito due to its association with polluted water and can be found in most California counties.

The Banded Foul Water Mosquito is a dark bodied, medium-sized mosquito with a prominent white band on its proboscis (beak) and white bands on the tarsi (feet). It is further characterized by black scales which form “o” spots on the underside of the blunt-tipped abdomen. This mosquito most closely resembles Culex tarsalisbut lacks the white stripe on the hind legs.

Diseases Transmitted

Foul Water Mosquitoes do occasionally create domestic, industrial and agricultural pest problems when they are present in large numbers. Although Western Equine Encephalitis and St. Louis Encephalitis has been isolated from natural populations of these mosquitoes, their reluctance to bite humans reduces their efficiency as disease carriers. This species has recently been identified as a carrier of West Nile Virus, a mosquito-borne disease that is rapidly spreading across the United States.

Life Cycle

Foul Water Mosquitoes have four life stages: egg, larva, pupa, and adult. The immature stages need standing water to complete their life cycle.

After an adult female lays her eggs they hatch into larvae (wrigglers), which feed on small organic particles and microorganisms in the water. Feeding occurs when they hang from the water’s surface by the tip of their tail (siphon) or by browsing along the bottom of their habitat. Because they are air breathing organisms they must return to the water’s surface to breathe. About one to two weeks are required for larval development. At the end of the larval stage, the mosquito molts and becomes the aquatic pupa (tumbler). The pupa is active only if disturbed, for this is the resting stage where the larval form is transformed into the adult. This takes about two days during which time feeding does not occur. When the transformation is completed, the new adult splits the pupal skin and emerges. Under optimum conditions, development from egg to adult takes about a week. However, all mosquito developmental times are dependent on the temperature and nutrients of the water in which they mature.

Adult Daily Activity

These mosquitoes may live for two or three weeks in the summer, but under cooler conditions the females may live for several months. In areas of moderate climate, adults and larvae may be found in every month of the year, but in areas with cold winters this species usually passes the winter as hibernating females in protected natural or artificial shelters such as cellars, outbuildings, wood piles, caves, culverts, etc. Mating may take place in conjunction with the male swarms.

Adult Flight Range

This species is capable of traveling 1-2 miles to seek a host, but is most commonly found near its aquatic habitat. The maximum recorded flight range is less than ten miles.

Adult Feeding

Female foul water mosquitoes seem to prefer feeding on birds, but on occasion will feed on livestock and humans. Males feed on nectar and plant juices. Females may also feed on plant juices, but usually must have a blood meal in order to develop their eggs. Nighttime is the peak feeding time for females of this species.

Eggs and Larvae

An adult female lays about 150-200 eggs in clusters called rafts, which float on the surface of the water until they hatch in about one to two days. The female usually prefers laying eggs in standing, polluted water such as sewage, street drainage, industrial wastes, dairy ponds, log ponds and backyard sources such as unused swimming pools, fouled ornamental ponds, cooler drain-water, and water in containers. A wide variety of other water sources may also be infested with the aquatic stages of this common mosquito.