Mosquitoes in California: At a glance

What are invasive Aedes mosquitoes, also known as "ankle biters"?

"Ankle biters" is a common nickname for invasive Aedes mosquitoes in California, particularly Aedes aegypti  and Aedes albopictus. These mosquitoes are aggressive daytime biters that often bite people around their legs and ankles. They can also breed in small amounts of standing water around homes and can spread diseases such as dengue, Zika, and chikungunya.

However, not all Aedes mosquitoes are invasive. Aedes is a group of mosquitoes that includes both native and invasive species in California. Here in Alameda County, native species such as the western tree hole mosquito (Aedes sierrensis) and salt marsh mosquitoes (Aedes dorsalis and Aedes squamiger) can also bite aggressively during the day.

For questions, consultations, or to report unusual mosquito activity, contact the Alameda County Mosquito Abatement District at 510-783-7744. District staff can help residents identify mosquitoes, eliminate breeding sources, and stay informed about mosquito activity.

Aedes aegypti

Aedes aegypti, also known as the yellow fever mosquito, is an invasive species native to Africa and is highly adaptive to its environment. It is a small black and white mosquito that readily bites people (its preferred host) and animals during the day. Ae. aegypti was first found in California in 2013 when it showed up in the counties of Fresno, Madera, and San Mateo. Since then, several other California counties have detected Ae. aegypti (map). Surveillance for Ae. aegypti is ongoing throughout Alameda County. This species is a potential public health threat due to its ability to transmit serious diseases such as dengue, yellow fever, chikungunya, and Zika.  Ae. aegypti can breed in any source of water that holds more than a bottle cap of water such as plant saucers, pottery, tires, bromeliads, etc. near humans and prefers to bite indoors. The obscure breeding areas make this mosquito especially challenging to find.

Aedes aegypti was found in Alameda County in 2024.

Learn more about Aedes aegypti  in Alameda County

Aedes albopictus

Aedes albopictus, also known as the tiger mosquito, is a very adaptable species native to Southeast Asia. It is black and white with a distinct white stripe down the back of its thorax. Primarily an outdoor biting mosquito, it will feed on a variety of hosts, including humans, typically during the daytime. This mosquito has entered California in the past but never established itself until 2011 when it appeared in the San Gabriel Valley and parts of Los Angeles. Ae. albopictus activity has expanded to include 5 counties (map). In Alameda County, surveillance for the potential introduction of Ae. albopictus is ongoing. Adult Ae. albopictus prefer to lay eggs in man-made containers with as little as a bottle cap of water such as plant saucers, tires, and even soda cans. This mosquito is a major public health concern because it is a competent vector for dengue, yellow fever, Zika, chikungunya, and dog heartworm.

Aedes albopictus has not been found in Alameda County.

Additional Resources

California Department of Public Health (CDPH) |  Invasive Aedes Mosquitoes

Centers for Disease Control and Prevention (CDC) | Aedes aegypti & Aedes albopictus