When is Mosquito Season in California?

lawn of a house in california

Mosquito season in California starts as early as February and lasts until November for most of the state. Peak months vary according to the region, but mosquitoes can be active all year round. Mosquitoes in California are not just a nuisance – but also a public health concern. Read to learn more about California’s mosquito season and how to prepare for it.

When is Mosquito Season in California?

mosquito season map
Photo Credit: Juan Rodriguez

In some parts of California, mosquito season begins in February and goes on until November. In other regions, it goes from March to September. But the overall warm climate of the state makes it possible to spot mosquitoes all year round.

The mosquito population begins to increase in spring when the temperatures start to rise after winter. Mosquitoes prefer temperatures above 50 degrees, as they cannot regulate their own body heat. Additionally, the spring rains form standing water sources, creating the perfect breeding grounds for mosquitoes. 

The combination of the ideal temperatures and the abundance of new breeding sites causes a boom in mosquito populations. Unfortunately, this also means a boom in mosquito-borne disease transmission.

Mosquito Season Month by Month

Here’s a monthly overview of how mosquito season works in California:

  • March: The spring rains form the first breeding habitats for mosquitoes.
  • May: The warmer weather makes mosquitoes even more active.
  • August: This month is peak mosquito season and when the risk of contracting mosquito-borne diseases is the highest. 
  • October: The weather starts to cool down, but mosquitoes are still active.
  • December to February: Some mosquitoes can still breed during winter months in California, so mosquitoes can still be spotted. However, their quantity is significantly reduced.

It’s important to note that some regional variations occur. In Los Angeles County and the rest of Southern California, for example, mosquito season usually has its peak in July and goes until October. A heavy winter rainfall can also worsen mosquito peak activity, as happened in the 2023 L.A. County mosquito season.

mosquito bite on a hand
Photo Credit: Piman Khrutmuang’s Images / Canva Pro / License

West Nile Virus in California

The most widespread mosquito-borne disease in California is the West Nile virus, with more than 7,500 human cases reported since 2003. The transmission of the virus occurs mostly during summer and early fall, when the Culex mosquito is most active. The best way to avoid getting infected with the virus is through preventing mosquito bites.


How Do I Prevent Mosquito Bites?

To prevent mosquito bites and reduce the risk of West Nile virus, the California Department of Public Health recommends the “Three Ds”:

DEET: Spray or apply EPA-registered insect repellents containing DEET, oil of lemon eucalyptus, picaridin, or IR3535. Always follow the directions on the label.
Dawn and Dusk: Avoid going out at dawn and dusk, as these are the preferred hours of the Culex mosquitoes. During these periods of the day, wear long sleeves and long pants (or insect-repellent clothing) and apply mosquito repellents.
Drain: Get rid of standing water in clogged gutters, flowerpot saucers, and old tires, which can become mosquito breeding sources. If there are water sources that can’t be drained (and aren’t for human consumption), like ponds, birdbaths, and unused swimming pools, control mosquito larvae by using mosquitofish or larvicides.

Are Mosquitoes Active During Winter?

Some mosquitoes in California stay active during winter, as is the case with the Winter Marsh Mosquito (Culiseta inornata). Luckily, this one does not transmit disease, but it can be a nuisance. But this is not common mosquito behavior for most species, as most mosquito species die or hibernate during winter.

How Many Mosquito Species are There in California?

There are currently 53 known mosquito species in California. Some are endemic and others are invasive, but here are some of the most common:

California Dreaming

Don’t wait there, dreaming of a mosquito-free California. Whether it is a summer or a winter’s day, Pest Gnome connects you to the best mosquito control experts in California. Get in touch today!

*Reference to the song California Dreamin’ by the musical group The Mamas & the Papas.

Main Image Credit: David Sawyer / Flickr / CC BY-SA 2.0

Teresa Joaquim

Teresa is a creative writer who holds a Master's degree in Psychology. Despite being a nature lover, she is terrified of cockroaches. As a native of the tropics, she is used to dealing with mosquitoes, although they still manage to bother her. Her favorite things are art, music, and playing with her two cats.