Invasive Aedes mosquitoes 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. More importantly, they are a risk to human health because they can carry diseases that make people very sick, like Zika, chikungunya, dengue, and yellow fever.

Species of invasive Aedes mosquitoes are found in some areas of Arizona and California. One species, Aedes aegypti, has been found in San Mateo County before, but has not been seen here since 2015. This file and interactive map created by the California Department of Public Health show where they are currently found in our state.

Although invasive Aedes mosquitoes have not been seen in our county recently, there is a high risk that they will be brought into our county again. These mosquitoes are spreading throughout California and have been found as close by as Santa Clara County, Santa Cruz County, and Contra Costa County.

The District continues to conduct intensive surveillance throughout the County, but 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.

Page last reviewed: June 6, 2024