When do mosquitoes come out in San Diego? From April through October, according to San Diego County.[1]
Mosquito screens installed by Total Screen keep your windows open and the mosquitoes outside.
In this guide we explain: when do mosquitoes come out in San Diego, what wakes mosquitoes up in Spring, & why coastal and inland mosquitoes behave differently.
Mosquito season runs April through October, and the Centers for Disease Control and Prevention says to “install or repair and use window and door screens,” so get mosquito screens installed before it starts.[9]
When Do Mosquitoes Come Out In San Diego?
San Diego County states that mosquito season usually runs from April through October.[1]
County crews begin proactive mosquito treatments in April, at the start of mosquito season.[1]
Mosquito activity climbs through Spring, peaks in the Summer heat, and eases in late Fall.
Mosquito activity drops in the cool months, but it does not stop.
California's public-health agency notes that mosquitoes are active year-round in California.[2]
The diseases mosquitoes can carry concentrate in the warm months.
What Wakes Mosquitoes Up In Spring
Mosquitoes are cold-blooded, so temperature runs their internal calendar.
U.S. Army health researchers report that mosquitoes stop flying once temperatures drop below 50°F.[3]
Mosquitoes do not migrate away for the Winter.
Mosquitoes wait out the cold as dormant adults, or they lay eggs that hatch in Spring.[3]
Below 50°F mosquitoes stop flying, but they wait out the cold nearby instead of leaving.
Mosquitoes become active again in the first warm week of Spring, once temperatures rise back above 50°F.[3]
Warmer weather raises the disease risk as well as the mosquito count.
A University of California, Berkeley analysis of Southern California found that as temperatures move into the 70-to-73°F range, the odds of finding West Nile-infected mosquitoes rise sharply.[4]
Coastal vs Inland Mosquitoes
The coast and the inland valleys run on different mosquito schedules.
For coastal areas of San Diego, high tides can increase mosquito activity.
The County's Vector Control program, which tracks and treats local mosquitoes, has noted that high tides leave salty standing pools which breed a daytime salt-marsh mosquito.[5]
The salt-marsh mosquito delivers a painful bite, but it does not spread human disease the way other mosquito species do.[5]
High tides drive mosquito activity along the coast, while heat drives it inland.
For the inland areas of San Diego, heat is the primary driver of mosquito activity.
As referenced in the Berkeley analysis above, hotter inland areas carry the highest risk of mosquito illness, like West Nile virus.[4]
Is There A Safe Time Of Day?
The Culex mosquitoes that spread West Nile virus are most active at dawn, dusk, and after dark.[6]
The invasive tiger mosquito, known locally as the “ankle biter,” bites in daylight instead.[7]
Aedes, the ankle biter, bites by day and Culex bites from dusk to dawn, so no hour is mosquito-free.
Between the two species, no hour of the day in San Diego is free of mosquitoes.
Windows are open through the daytime hours the ankle biter bites, and open again on the warm evenings when the Culex fly.
Standing Water & Mosquito Breeding
Every mosquito lays its eggs in, or near, standing water.
The County notes that in warm weather a mosquito goes from egg to biting adult in about a week or less.[8]
One forgotten container in a backyard can raise a full brood in that week.[8]
A plant saucer holds enough standing water to raise a full brood in about a week.
Look around your property for standing water that you can dump out.
The containers that hold water around a San Diego yard are ordinary, and easy to miss:
- Buckets, Old Tires & Wheelbarrows: anything left out that holds a rain or hose-water puddle.
- Birdbaths, Pet Bowls & Plant Saucers: small containers that get refilled every few days.
- Clogged Gutters & Unmaintained Pools: standing water that collects out of sight.
The County's position is that finding, dumping, and treating standing water is the best way to control mosquito problems.[8]
Standing water indoors counts too, which is what our guide to how to get rid of mosquitoes in your house covers.
What Keeps Mosquitoes Out All Season
A mosquito window screen keeps mosquitoes out at every hour of the day, which no repellent or habit does.
A proper mosquito window screen has a frame which is attached flush to the window, or snugly seated within a channel.
An effective mosquito window screen must also have intact mesh, free from holes, rips, and tears.
Torn mesh and a gap at the frame let mosquitoes in; taut mesh in a snug frame does not.
Torn mesh and a loose frame are both things a homeowner can confirm in about two minutes, and our guide explains how to check a window screen.
Does Screen Mesh Size Matter For Mosquitoes?
Total Screen installs a standard 18×16 mesh, which is effective against most mosquitoes.
If you need a stronger defense against smaller flying insects, Total Screen can install a 20×20 no-see-um mesh instead.
Total Screen builds both weaves, and most San Diego homes only ever need the standard one.
Either weave only works while the screen still holds its shape, and a screen can develop a hole or a gap between one season and the next.
Our guide to “can mosquitoes get through window screens” explains where the mesh fails.
Get Ahead Of Mosquito Season
The answer to when do mosquitoes come out in San Diego is April, so the best time to check your screens is before the first warm week.
If the first warm week has already passed, check them this week instead.
Total Screen repairs, rescreens, and replaces window and door screens across San Diego, often with a same day or next day appointment.
Total Screen measures every window opening before building a replacement screen.
Call Total Screen at (619) 871-7610 for a free on-site estimate.
Or click here to fill out our 2-question contact-form, and we will get back to you right away.
Contact Total Screen to get your window screens checked before mosquito season starts.
Disclaimer: Total Screen is not a mosquito-control or public-health authority. This article is provided for informational purposes only, and is based on our online research of publicly available documents from the County of San Diego, the California Department of Public Health, the Centers for Disease Control and Prevention, and the other sources listed below. To report a mosquito problem, or to ask about treatment on your property, contact the County of San Diego's Vector Control Program.
Sources
- County of San Diego — mosquito season "usually April-October"; County Vector Control begins proactive treatments in April. countynewscenter.com
- California Department of Public Health — West Nile Virus FAQ (mosquitoes active year-round in California). westnile.ca.gov
- U.S. Army / Defense Health Agency — "Where Do Mosquitoes Go During the Winter?" (below 50°F they stop flying; dormancy). army.mil
- UC Berkeley News — warming climate & West Nile virus in Southern California (70–73°F; higher inland risk). news.berkeley.edu
- ABC 10News San Diego — coastal mosquito activity spikes after high tides (Aedes taeniorhynchus, the black salt marsh mosquito; “these high tides leave pockets of water that turn into brackish water, and it breeds these mosquitoes”; “very active during daytime hours”; “While the bites from these mosquitoes are known to be painful… they do not spread human disease the way other mosquito species do”). 10news.com
- California Department of Public Health — Guide to Important Mosquitoes in California, PDF (Culex biting times). cdph.ca.gov (PDF)
- County of San Diego — Invasive Aedes Mosquitoes ("Bite during the day, especially around the legs and ankles"). sandiegocounty.gov
- County of San Diego, DEHQ — Mosquitoes / Fight the Bite (“in a week or less they emerge as a biting adult”; “Finding, dumping, and treating standing water is the best way to control mosquito problems”). sandiegocounty.gov
- Centers for Disease Control and Prevention — Mosquito Control at Home (“Install or repair and use window and door screens”). cdc.gov