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San Diego mosquito season is off to a slow start

San Diego has mosquitoes all year, because there’s no hard freeze, and typically they become more numerous and aggravating when the weather warms up in the spring.

“We consider mosquito season to start in about April and go through October,” said Allison Bray, an environmental health specialist with San Diego County Vector Control.

Bray said this year people were likely suffering fewer bites because the season is off to an unusually slow start. Yes, it’s been rainy and mosquitoes breed and produce larvae in water, but there are other factors involved.


“Winters with heavy rain have effects that are hard to predict,” Bray said. “It has kept our rivers and streams running. That means it’s not a friendly environment for bugs that need stagnant water. We’re also seeing the weather staying cold longer and mosquitoes reproduce faster when the weather is warmer.”

So swift rivers and chilly temperatures are holding down the populations of mosquitoes, and that’s why San Diego County Vector Control is not snaring as many of the bugs in their outdoor traps.

Standing, stagnant water is where mosquitoes like to breed. It’s the kind of water you find in canyon ponds, rain barrels and poorly maintained backyard pools — called a “green pool” by mosquito control officials.

“It’s not being chlorinated. It’s not being filtered. And algae is starting to grow in it. And the pool takes on this green color,” Bray said. “Unmaintained green pools can be a really big source of mosquito breeding, especially in people’s neighborhoods.”

To keep the bugs to a minimum, she said, San Diegans should empty any outdoor water vessels that can catch the rain. If you have a pond or another kind of standing water you can’t empty or drain, the solution might be mosquito fish.


There’s a tank of mosquito fish in the lobby of the county building that houses Vector Control. Bray said the guppy-size fish can eat more than their weight in mosquito larvae daily, and local residents can get them free from San Diego County.

This pond in Tecolote Canyon in San Diego is the kind of standing water that is a good breeding place for mosquitoes. May 27, 2023.
Thomas Fudge
This pond in Tecolote Canyon in San Diego is the kind of standing water that is a good breeding place for mosquitoes. May 27, 2023.

There are at least 25 species of mosquitoes in the county. Many of them are invasive, such as the Aedes aegypti, which, Bray said, really like the taste of us.

“They’re what we sometimes call backyard breeders. They want to lay their eggs as close to humans as possible because we are one of their favorite food sources,” she said.

The mosquitoes that bite us and suck our blood are the females. They need the iron and proteins in blood to nourish and produce their eggs.

The Aedes aegypti, originally from West Africa, are very good at carrying yellow fever and zika virus. In San Diego they don’t carry those diseases because they aren’t endemic here.

Mosquitoes in California do carry West Nile Virus, but that’s usually asymptomatic. And recently there have been fewer than five confirmed cases of it every year in San Diego County.