Return to the Information Directory Return to Mosquito Biology page
The Most Important Species in Alameda County


These eight mosquito species cause 99% of all service requests (calls from the public) and require most of the field control efforts by the Alameda County Mosquito Abatement District.

Aedes dorsalis (Salt marsh mosquito)

This species is found year round in tidal salt marsh areas. The eggs are laid in the marsh and hatch when the marsh is filled by high tides. Control is by application of biorationals and physical modifications. Most of the sources are in ecologically sensitive areas and require great care to avoid damage. Adults are very aggressive, fly moderate distances, and are noticeable near the marshes. This species is capable of producing very high numbers near marsh areas.

Aedes washinoi (Woodland pond Mosquito)

This mosquito is produced in woodland depressions that fill with water. Eggs are laid on the mud and organic material along the edges of receding water in these areas. Adults are generally present in the early Spring, are very aggressive, and may be found in large numbers. Most of the control effort on this species is by use of biorational materials and mosquitofish.

Aedes squamiger (Winter salt marsh mosquito)

This species is produced in the marshes along the edges of the Bay. The eggs are laid on the marsh in the Spring and hatch as soon as the marsh fills with rain water in the Fall. Adults emerge the following Spring. Most of the control effort occurs during the winter. Control is by physical modifications to the marshes and by spraying with biorational materials. Many of the marsh sources are ecologically sensitive areas requiring coordination with other agencies. Adults can fly long distances The adult is a very aggressive biter and is very noticeable to the public. This species is capable of reaching very high numbers.

Aedes sierrensis (Tree hole mosquito)

This species breeds in tree holes (rot cavities or deprressions in trees which hold water). If near trees and partially filled with organic debris, containers such as tires and buckets may produce these mosquitoes. The eggs hatch when the tree hole or container fills with water. The adults hatch in March and remain in the area until early Summer. This mosquito has a short flight range, is an aggressive biter, and is the primary vector of Canine Heartworm in Alameda County. It is found in any area where suitable tree holes are found. This district is currently testing biorational materials for control of this species.

Culex pipiens (House mosquito)

This species causes the largest number of service requests, and is an excellent carrier for West Nile Virus. This mosquito is generally an urban problem. The adult can be found all year and breeds in storm drains, catch basins, utility vaults, septic tanks, flooded basements, sumps, and in just about any water container found near man. The adult readily enters homes, and bites at night. Because of the type and variety of breeding sources it takes many hours to locate the cause of a problem. Continual treatment and monitoring of sources is required to maintain control these mosquitoes.

Culex tarsalis (Encephalitis mosquito)

This mosquito is produced in rain pools, marshes, swimming pools, ponds, and other fresh water sources. Although this species does not produce a large number of the District's service requests, it requires a large part of the control effort to prevent the spread of encephalitis in Alameda County.  It's also an excellent carrier for West Nile Virus.  This species feeds primarily on birds and is only moderately aggressive towards man. This species is capable of reaching very high numbers and is a potential for mosquito-borne disease transmission. Control is by application of biorational materials, mosquito fish stocking, and physical modifications to sources.

Culiseta inornata (Winter marsh mosquito)

Females of this species rest during the summer and become active in the Fall after the first rains. Eggs are laid on the surface of rain filled ponds in the Fall. Many generations can be produced in one season. This mosquito bites at dusk in the Fall and Spring and is moderately aggressive, quite large, and may reach very high numbers. It is very noticeable to the public because of its size and activity. This species is generally found close to temporary fresh water sources. Most of the control effort is by using biorational materials.

Culiseta incidens (Fish pond mosquito)

This mosquito is produced in fish ponds, creeks, and containers. It is the second major cause of service requests for the district. Small sources can produce sufficient numbers to cause discomfort in a neighborhood. This mosquito is moderately aggressive, bites in the evening or shade, and is very noticeable because of its large size. It is primarily a problem of urban and suburban areas. Control is by use of biorationals and the use of mosquitofish.