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2023 Mosquito Surveillance

 This chart shows the average number of adult mosquitoes collected in CO2 traps per trap per night night during February 2022. Data are shown for the six most common species of mosquitoes in San Mateo County.Adult Mosquitoes

Adult abundance of all mosquito species are very low, as is consisitent with the five-year average in February. The abundance of adult mosquitoes is expected to remain low until spring.

Carbon-dioxide trap data

This table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of February compared to the five-year average for the six most common mosquito species in San Mateo County.

SpeciesFebruary 20225-year February average
Culex pipiens1.82.5
Culex tarsalis0.10.3
Culiseta incidens<0.10.3
Culex erythrothorax00.1
Aedes sierrensis00
Aedes washinoi0<0.1


This chart shows the 5-year average number of mosquitoes collected per trap night by month for the previous 5 years. Data are shown for the six most common species found in San Mateo County.

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Larval Mosquitoes

Side view of a person with short hair and a tan colored baseball hat and blue surgical mask on. The person appears to be standing in a field, with a bright yellow vest and holding a metal stick that has a white plastic cup on the end of the stick. The person is looking in the cup.
Vector Control Techinician Evan Ostermann checks his dipper for larvae from a marsh.

During February, larval surveillance focused on monitoring seasonal natural sources, such as freshwater impounds and marshes, while continuing to check backyard sources. Additionally, water from February rains can collect under houses and provide a sheltered place for larvae to develop. District staff collected 154 larval samples in February. Technicians use a dipper to take a sample of water and visually inspect it for mosquito larvae. If larvae are present, the sample is taken back to the District laboratory for species identification.

The most frequently occurring species, in 39% of samples, was Culiseta incidens. This mosquito is found year-round in San Mateo County in a variety of sources, especially backyard fountains, and fishponds.  These mosquito species are not known to transmit human disease. Other commonly collected species in February were marsh breeding mosquitoes such as Culiseta inornata, Aedes washinoi, and Aedes squamiger. Although these species do not currently vector any diseases in this region, they are known to be voracious day-biting mosquitoes, especially Ae. squamiger. The District takes particular care to monitor the saline or brackish marsh areas that breed Ae. squamiger, as this species has the potential to emerge in huge numbers when the weather warms up.

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This graph shows the number of larval samples containing each mosquito species collected in February 2023. Larval samples commonly contain multiple species.

 Page last reviewed March 6, 2023

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