It appears as if the rain has stopped, at least for now, but that wasn't the case in recent weeks. Days of rain including what weather forecasters call an atmospheric river caused flooding, landslides, and a host of other issues, including standing water in front and backyards in Contra Costa County. And as any amount of standing water, even as little as what can fit into a water bottle lid can produce mosquitoes, it's critically important to make sure you dump and scrub any item holding water in your front or backyard to reduce the risk of mosquitoes and the viruses they can spread.

Contra Costa County is home to 23 types of mosquitoes. There are winter mosquitoes, which are out right now; West Nile virus (WNV) mosquitoes which are mostly active during late spring, summer, and early fall; tree hole mosquitoes that can transmit dog heartworms; and more than a dozen other types of mosquitoes, each with its own unique habits.

There is another type of mosquito that is not native to California but has already changed the quality of life in Southern California and the Central Valley. In August of 2022, Contra Costa Mosquito and Vector Control District (District) employees found this mosquito, Aedes agypti (the yellow fever mosquito) in Martinez, and then again in 2024, we found these mosquitoes in Concord and Antioch.

These mosquitoes are particularly dangerous because they can transmit the viruses that can cause Zika, dengue fever, yellow fever, and chikungunya. Similar to WNV mosquitoes, these mosquitoes are most active in late spring, summer, and early fall, but unlike WNV mosquitoes, Aedes aegypti, also known as the yellow fever mosquito, will bite during the day when people are more likely to be outdoors, and are "sneaky" biters, so you may not be aware of the bites until they start itching afterward.