Invasive Aedes mosquitoes are small, black-and-white mosquitoes that bite during the day. They can spread diseases like dengue, chikungunya, Zika, and yellow fever.

Invasive Aedes aegypti are not native to San Mateo County, California, or even North America. They do not belong in our ecosystems, and they can make people very uncomfortable because they bite during the day and even bite indoors. 

Species of invasive Aedes mosquitoes have become established throughout many US states. These mosquitoes are spreading throughout California and have now been found throughout the Bay Area. This file and interactive map created by the California Department of Public Health show where they are currently found in our state.

Aedes aegypti has occassionally been found in San Mateo County before. Residents of Menlo Park may remember the 2013-2015 detections and work that the District did to eradicate the mosquito.

As of July of 2026, Aedes aegypti has again been found in San Mateo County - this time in a small areas of Redwood City, North Fair Oaks, and San Carlos. District staff are visiting properties in the area to determine how widespread the problem is, and are working with local residents to control (and hopefully eradicate!) the mosquito.

The District continues to conduct intensive surveillance throughout other areas the County, and you can help out by reporting suspected invasive Aedes mosquito sightings. The sooner we know that these invasive mosquitoes have arrived in our county, the better chance we have of stopping them. Call 650-344-8592 or report on our website.

 

 

Page last reviewed: October 26, 2026