Invasive Aedes aegypti Mosquitoes Have Been Detected Again in the County
For more information on this invasive mosquito visit our Aedes aegypti informational page. For scheduled treatments regarding this mosquito, visit Wide Area Larvicide Spraying page.
Aedes aegypti mosquito has distinct black and white stripes on its legs and body
Invasive Aedes aegypti (pronounced AY-dees ah-JIP-tie) mosquitoes are much different than our native mosquitoes. This mosquito is aggressive and likes to bite multiple times and especially during the day. They come from tropical and subtropical areas of the world. Since they are not native to California, they don't live well in the state's natural areas, but they do live and thrive in cities and backyards near people. In recent years, they have spread to many new places around the world.
These mosquitoes can spread easily to new areas by hitching a ride. They glue their eggs to plants like lucky bamboo or items like tires. They can also travel by following people into their cars.
Special Concern
This mosquito is of special concern because it has the potential to transmit several diseases that are currently not in the county, including Zika, dengue, yellow fever, and chikungunya.
We often investigate travel cases related to these diseases. Travel cases happen when someone from our county travels to a place where they are bitten by a mosquito that makes them sick with one of these diseases. We monitor these cases because if there are active travel cases, and the mosquito that can spread these diseases is in the same area of the travel case, it increases our risk of having these diseases spread in our community (also known as locally transmitted cases). This is another reason why we don’t want this mosquito to become permanent in our community.
Your Help Matters
Mosquito control is a community effort. We are doing everything we can to stop the spread of this invasive mosquito, but we need your help to successfully eliminate this mosquito from our community.
Receive Alerts
Subscribe to the County's emergency alert system, AlertSCC, to receive specific neighborhood notifications aboutinvasive mosquito detections and mosquito treatments happening in your community.
You can receive an email, phone call, and/or text on any of the information below:
Invasive mosquito detections in your specific neighborhood
Mosquito control treatments in your specific neighborhood
Prevent water from collecting in containers like plant pots, saucers, barrels, bins, buckets, and old tires. You can do this by turning them over, storing them inside or under covered areas, or getting rid of them if it is no longer needed.
Scrub and clean outdoor items around your home that collect water.
Cover outdoor trash cans, toys, and recycle bins. Keep items that can hold water dry, away from rain, and out of the reach of sprinklers.
Fix leaky water faucets and broken sprinkler heads and avoid overwatering lawns and plants.
Make sure windows and door screens are in good condition, with no holes or tears, and fit tightly.
Mosquito Bite Protection
To protect yourself from mosquito bites and mosquito-borne diseases, you can follow the steps below.
Insect Repellents - Use insect repellents with EPA-registered ingredients like DEET, picaridin, IR3535, or oil of lemon eucalyptus. Always follow the instructions on the label.
Attire - When spending time outside, wear:
Long-sleeve shirts
Long pants
Socks
Closed toe shoes
Report
Report mosquitoes with black and white stripes.
Report mosquitoes that bite during the day and at night (even inside).
Aggressive Biters - These mosquitoes are very aggressive and will bite multiple times. They will bite at any time of day, usually during the day, and will even follow you inside to bite.
Prefer Humans - They like to bite humans the most and usually bite around the ankles. Their bites can leave many large and itchy bumps. Because they mainly bite people, the risk of spreading diseases to humans is higher.
Container Breeders - Aedes mosquitoes like to lay their eggs on the sides of containers that have standing water. For example, buckets, bird baths, pet dishes, plant pots and saucers, old tires, stems of plants growing in water, etc. They often lay their eggs around backyards, where it’s hard for mosquito and vector control teams to check. These mosquitoes only need a tiny bit of water to lay their eggs.
Hardy Eggs - Aedes eggs look like thin lines of dirt to the naked eye. These eggs are very tough and can survive several months without water. The eggs will hatch when they touch water and the weather conditions are perfect for them.
Black and White Stripes - Aedes mosquitoes are small, about 1/4 inch, with black and white stripes on their back and legs.
Fly Short Distances - Aedes mosquitoes don’t fly very far. Unlike our native mosquitoes, they usually stay within 500 feet of where they hatch.
Difficult to Manage - Aedes aegypti mosquitoes are hard to control once they are established because they do well in cities and their eggs can survive years through dry conditions.
What We are Doing
Surveillance
Mosquito traps seen from left to right: EVS (formally known as Encephalitis Vector Surveillance Trap), BG Sentinel, Ovicup, and BG-GAT
We have a detailed plan to monitor and respond to this mosquito species. We've stepped up our efforts to find these mosquitoes by setting traps for adult mosquitoes and their eggs within 500 feet of where they were originally detected. Examples of our mosquito traps can be seen to the right.
Community Engagement
We are committed to keeping our affected county residents informed. We are taking several approaches to get the word out.
Door-to-Door
Our team is going door-to-door in the affected neighborhoods to talk to residents and inspect for mosquitoes and control them if they are found. We are working closely with the affected community members to get rid of standing water where this mosquito can lay eggs.
Access to Backyards: It is very important that residents in the affected area let us enter backyards so we can set traps, check for mosquito larvae, and treat them if needed. We are placing mosquito traps and bait stations in yards to help reduce the number of invasive mosquitoes in the neighborhood and monitor infestation. Access to yards is extremely important for us to stop this mosquito from spreading.
Notices: If residents in the affected area got a notice like a flyer or door hanger from us, but didn’t get a chance to speak to one of our technicians, please contact us as soon as possible to request a free mosquito inspection. This will help us check for invasive mosquitoes.
Privacy Concern: If residents in the affected area are worried about their privacy, please know our staff is only allowed to set traps, check for mosquitoes, and control mosquitoes that are found. They are not allowed to do anything else on the property. Our staff will have clear ways to identify themselves as district employees.
Detection and Treatment Notifications
We are committed to providing affected residents notice of any detection or treatment for this mosquito taking place in their community.
Postcards: Residents in the affected neighborhoods will get a postcard in the mail with information about the invasive mosquito issue and links to more resources.
AlertSCC Notifications: Residents who are signed up for the County’s emergency alert system, AlertSCC, will receive a notification (phone call, text, and/or email) about the mosquito detection in their neighborhood and any scheduled treatment plans. If you are not yet signed up for AlertSCC, you can subscribe here.
Email Notifications: To protect public health, we get email addresses of residents in affected neighborhoods from the County of Santa Clara Registrar of Voters. These residents receive an email about the mosquito detection and information on any scheduled treatments in their area.
Mosquito Control
When needed, we use larvicides (pesticides that target mosquito larvae) to stop mosquito larvae from growing into flying adult mosquitoes. Larvicides are made from natural materials like bacteria found in soil and insect growth hormones.
We use many methods to apply pesticides. This includes backpack sprayers and machines mounted on trucks for wide area larvicide spraying treatments. If needed, we will also use EPA-approved adulticides (pesticides that targets adult biting mosquitoes) to kill mosquitoes that have reached the biting stage. Adulticides are used only when needed to quickly prevent the spread of disease, control biting mosquitoes, or the spread of invasive mosquitoes. All larvicides and adulticides (pesticides) we use are approved by the Federal and State environmental protection agencies.
We are also using bait stations to reduce the population of this aggressive mosquito.
Our Native Mosquitoes
The county is home to about 20 native mosquito species like the common house mosquito (also known as Culex pipiens), the cool weather mosquito (also known as Culiseta incidens), the Western encephalitis mosquito (also known as Culex tarsalis), and other species. Our native mosquitoes mostly bite at dusk and dawn. They transmit diseases like West Nile virus, Western equine encephalitis, and St. Louis encephalitis. We see diseases like West Nile virus every year in the county.
Detection Timeline:
Over the past ten years, these mosquitoes have spread to warmer parts of California. They are currently detected in 19 counties. In 2022, two Aedesaegypti mosquitoes were detected in Santa Clara County. We acted quickly to stop their spread and continued to check for them throughout the year. We did not detect any additional invasive Aedes aegypti mosquitoes until March 2024. At the end of 2024, this mosquito had been detected in six different locations in the county.
2025 Updates:
As of April 2025, we have detected these mosquitoes in some of the same neighborhoods that were affected last year. This reappearance means the mosquito's eggs successfully survived the winter and are hatching now that the weather is getting warmer. To stay informed of any future detections and treatments, sign up for our mosquito alerts.
