Top mosquito cities in the western U.S.

As the warm summer months roll in, mosquitoes emerge and become a nuisance for nearly everyone. These tiny pests aren’t just annoying—they’re also known vectors for numerous diseases that pose serious health risks.

There's a common misconception that mosquitoes aren't a big problem in western states like California, but this is far from the truth. More than 50 species of mosquitoes are found throughout California, thriving in diverse habitats ranging from low-elevation deserts to mountain meadows over 10,000 feet high.¹ 

While many of these species are uncommon and rarely a threat, several actively feed on humans and can transmit serious diseases. The mosquitoes of major concern in California belong to the genera Culex, Aedes, and Anopheles—some of which are responsible for spreading illnesses such as West Nile virus, Zika virus, malaria, and even heartworm in pets.

So, which cities in the western United States experience the highest mosquito activity and report the most mosquito-borne diseases? A few of the top mosquito cities include Los Angeles, San Francisco, Palm Springs, Sacramento, and San Diego.

If mosquitoes are becoming a problem, Western Exterminator’s mosquito control experts can treat your property to help get rid of mosquitoes in all life stages and create an effective barrier against them.

Los Angeles, CA

Los Angeles is often considered a hot, dry city with little rain, but that’s not entirely true. While droughts have been a recurring issue, L.A. does experience rainy seasons in late winter and early spring. The combination of moisture and warm temperatures creates ideal conditions for mosquitoes to thrive, making it the top mosquito city in the U.S.

Mosquito season in L.A. typically begins in early spring as temperatures warm up and lasts through late fall, tapering off when temperatures drop below 50°F. The most common species found here include the Southern house mosquito (Culex quinquefasciatus), which is a primary carrier of West Nile virus, and the invasive Yellow fever mosquito (Aedes aegypti) and Asian tiger mosquito (Aedes albopictus), which can transmit Zika virus, dengue, and chikungunya. These aggressive daytime biters are a growing concern in urban areas and use small pockets of standing water to breed.

San Francisco, CA

Unlike the scorching summers of southern California, San Francisco’s mild, foggy climate might not seem like an ideal breeding ground for mosquitoes. However, the city and surrounding Bay Area still experience seasonal mosquito activity, particularly in areas with standing water, marshes, and slow-moving creeks.

Mosquito season in San Francisco typically begins in late spring as temperatures rise and lasts through early fall. While the cooler, breezy conditions help limit mosquito populations compared to inland California, the various water sources and occasional warm spells allow them to persist.

The most common species in San Francisco include the Western encephalitis mosquito (Culex tarsalis), known for transmitting West Nile virus, and the Northern house mosquito (Culex pipiens), which can also carry West Nile virus and St. Louis encephalitis. 

Palm Springs, CA

Palm Springs' warm desert climate might seem inhospitable to mosquitoes, but the presence of irrigation, golf courses, pools, and seasonal rains creates plenty of breeding grounds for these pests. Mosquito season in Palm Springs typically runs from early spring through late fall, though mosquitoes can remain active year-round in warmer conditions.

The most common mosquitoes in the area include the Western encephalitis mosquito and the Southern house mosquito. These mosquitoes are known carriers of West Nile virus and St. Louis encephalitis. Yellow fever mosquitoes and Asian tiger mosquitoes are also an invasive species capable of spreading Zika virus, dengue, and chikungunya. 

Due to the hot, dry environment, mosquito activity in Palm Springs tends to spike after monsoon storms or heavy irrigation, which provides the standing water they need to reproduce. These conditions allow mosquitoes to persist, making it one of the top mosquito cities on the West Coast.

Sacramento, CA

Sacramento’s warm climate and proximity to water sources make it a hotspot for mosquito activity. Mosquito season typically begins in early spring (March or April) and lasts through late fall (October or November). Activity in this top mosquito city peaks in the summer when temperatures are high and conditions are ideal for breeding.

Common mosquito species in Sacramento include the Western encephalitis mosquito, Southern house mosquito, Yellow fever mosquito, and the Asian tiger mosquito. West Nile virus is the most commonly reported mosquito-borne disease in Sacramento. St. Louis encephalitis is occasionally detected in California, which is spread by Culex mosquitoes. 

San Diego, CA

San Diego’s warm climate and coastal location create an environment where mosquitoes can thrive nearly year-round, especially in areas with standing water. Mosquito season in San Diego typically starts in early spring (March or April) and extends through late fall (November). However, due to the region’s mild winters, mosquito activity can persist year-round in some areas, especially after rain.

Common mosquito species in San Diego include the Western encephalitis mosquito, Southern house mosquito, Yellow fever mosquito, and the Asian tiger mosquito. Like Sacramento, West Nile virus is the most frequently reported mosquito-borne illness, and St. Louis encephalitis is occasionally detected in the region. There is also the potential risk of Zika, dengue, and chikungunya, although it is not as widespread in San Diego.

Mosquito prevention

Living in a mosquito-prone area means protecting yourself from bites is essential. Beyond the annoyance, mosquitoes can transmit serious diseases and cause red, itchy welts. The best defense is prevention—here’s how you can help reduce your risk of mosquito bites:

• Use insect repellent containing DEET, picaridin, and/or oil of lemon eucalyptus (OLE). These are among the most effective options for keeping mosquitoes away.
• Limit outdoor activity during peak mosquito hours, which are dusk and dawn. If you must be outside, wear protective clothing and apply repellents to exposed skin.
• Wear long sleeves and pants to minimize exposed skin. Light-colored clothing is best, as mosquitoes are more attracted to dark colors.
• Eliminate standing water around your home, including birdbaths, planters, buckets, tires, and clogged gutters. Mosquitoes only need a small amount of water to breed.
• Use outdoor fans on porches, patios, and near seating areas. Mosquitoes are weak flyers, and the breeze from a fan can help keep them away.
• Use mosquito traps, such as UV light traps or CO₂-based traps, to help reduce adult mosquito populations.

Western Exterminator mosquito treatments

Whether you’re in one of the top mosquito cities on the West Coast or not, your local Western Exterminator mosquito control experts are ready to help. Our mosquito control process starts with a thorough inspection of your property to identify potential mosquito breeding sites and resting areas. From there, we implement a targeted treatment plan to help eliminate adult mosquitoes, eggs, and larvae.

Our proactive treatments create a protective barrier around your home, reducing mosquito populations. With our expert approach, you can reclaim your outdoor spaces and enjoy your yard without the nuisance of buzzing, biting pests. Contact Western Exterminator today!

1Source:https://ipm.ucanr.edu/PMG/PESTNOTES/pn7451.html#:~:text=More%20than%2050,and%20Anopheles 

2Data sourced from Terminix. For more information, visit Terminix Top Mosquito Cities