Mosquitoes
About Mosquitoes
There are about 20 species of mosquitoes in our county, including the common house mosquito (Culex pipiens), cool weather mosquito (Culiseta incidens), Western encephalitis mosquito (Culex tarsalis), the summer salt marsh mosquito (Aedes dorsalis), and the winter salt marsh mosquito (Aedes squamiger).
Mosquitoes go through metamorphosis like butterflies. Their life cycle goes through three water stages before reaching the flying and biting adult stage we tend to see during warm months. Mosquitoes need stagnant water to lay their eggs and can do so in as little as a bottle cap of water. Under the perfect environment, mosquitoes can go from egg to flying adult in less than a week.
Why are Mosquitoes Important?
Mosquitoes are the most dangerous insect in the world. Every year, over one million people worldwide die from the bite of an infected mosquito. Some mosquitoes are capable of transmitting diseases such as West Nile virus, dengue fever, and malaria. However, not all mosquitoes transmit the same diseases and not all mosquitoes are infected.
In California, West Nile virus (WNV) is the most common mosquito-borne disease (disease caused due to an infected mosquito). Since 2003, there have been 395 WNV-related deaths in the state. We detect WNV-infected mosquitoes in the county every year and have a detailed action plan in place to prevent a WNV human infection using Integrated Pest Management methods.
To learn more about West Nile virus in California, visit the California Department of Public Health webpage.
To learn more about West Nile virus in Santa Clara County, visit our West Nile virus webpage.
Our goal to is to prevent a human from getting sick from a mosquito-borne disease. We do this by keeping mosquito populations low and stopping them from reaching the flying adult stage.
Services
We offer a variety of services to assist with mosquito issues.
You can also help stop mosquito and West Nile virus problems by reporting the following:
How can I Protect Myself?
You can protect yourself from mosquitoes and stop the spread of disease like West Nile virus by doing the following.
On your property:
- Inspect for standing water on a weekly basis.
- Drain or turn over anything that can hold water, such as flowerpots, planter bases, outdoor pet dishes, buckets and old tires.
- Clean items like bird baths and pet bowls once a week to remove any mosquito eggs.
- Clear debris from rain gutters on a regular basis to allow water to flow.
- Properly screen rain barrels, cisterns, and irrigation drains to prevent mosquito access.
- Fix leaky water faucets and broken sprinkler heads and avoid overwatering lawns and plants.
- Ensure window and door screens are in good condition with no holes or tears and are tight-fitting.
- Ensure swimming-pool water level is adequate for proper circulation and filtration.
- Place mosquitofish in neglected pools/spas, ornamental ponds, water troughs and other artificial bodies of water. Free mosquitofish can be requested online.
Around your neighborhood:
Outdoor activities:
- Limit outdoor activities during dusk and dawn – these are the times when the mosquitoes that transmit WNV are most active.
- If you notice day biting mosquitoes, mosquitoes with black and white stripes, or get multiple mosquito bites around your ankles, please report this to us immediately as it might be an aggressive and invasive mosquito.
- If spending time outdoors, dress in long-sleeve shirts and long pants, preferably in light colors – mosquitoes are mostly attracted to dark colors.
- Apply insect repellent that contains DEET, IR3535 or oil of lemon eucalyptus, always following label instructions.
Disease Monitoring
We have a special program to monitor the presence of mosquito-borne diseases like West Nile virus, Western equine encephalitis, and St. Louis encephalitis which are diseases transmitted by our native mosquitoes. However, we also monitor for invasive mosquitoes, because their presence could lead to a higher risk of exposure to other diseases like Zika, dengue, and yellow fever, all diseases that are not currently in the county. We monitor the abundance of mosquitoes and monitor disease activity year-round.
- We use a variety of traps to monitor mosquito abundance and mosquito species present in the county. The main traps used are gravid traps and EVS (Encephalitis Vector Survey) traps.
- Gravid traps are filled with water that is prepared with hay and alfalfa, which attracts gravid (pregnant) female mosquitoes into the trap. The trap creates an upward current of air, blowing mosquitoes into a collection bag.
- EVS traps use carbon dioxide (CO2) as the primary attractant. They are filled with dry ice, which emits the CO2, and attracts mosquitoes. A small fan pushes them down into the attached mesh net.
- The trapped mosquitoes are then placed into a chest with ice and brought back to our lab where they are sorted by species, sex, and trap location. These groups are known as pools.
- Mosquitoes are then tested for disease using a PCR (polymerase chain reaction) test (similar to the process of a COVID-19 test). The test detects if any of the mosquitoes in the pool were infected with a disease like West Nile virus (WNV).
- If we find a positive virus detection, it prompts an adult-mosquito-control treatment to occur as the risk of a WNV human infection is now significant. We aim to prevent a human from getting sick from WNV and other mosquito-borne diseases.