Noticed more mosquitoes lately? You’re not imagining it

By Aaron Atencio | TrulySD

If it feels like you’ve been swatting more mosquitoes than usual this fall, you’re not imagining it.

San Diego County’s own surveillance numbers show West Nile virus turning up in local birds at the highest level in a decade. And after Tropical Storm Rachel’s rain, there’s a short window right now to stop the next round of biters before they hatch in your backyard.

We talked with Allison Bray, a program coordinator with the County of San Diego’s Vector Control Program, about what’s behind the buzz and what you can do about it this week.

Why there are more mosquitoes this year

The short answer is heat.

“Pretty much any of the several different species of mosquitoes we’ve got here, all of them are going to do better when it’s warmer, when it’s more humid,” Bray said. “This summer it’s been super warm. The nights have been really warm, and we didn’t really have that cold of a winter at the beginning of the year. So all of that’s just made it possible for the mosquitoes to multiply really quickly.”

According to Bray, this year’s activity is in line with what the County expects in a particularly warm year. The connection is clear: this year was warmer than the last couple of years, and it came with more mosquito problems.

The West Nile numbers

The bigger concern isn’t just how many mosquitoes there are. It’s what some of them are carrying.

West Nile virus lives in bird populations and spreads to people when a mosquito bites an infected bird and then bites a person. The County tracks it by testing dead birds and trapped mosquitoes. As of early October, the County had confirmed West Nile in 58 dead birds and 104 batches of mosquitoes this year. That bird count compares with 34 for all of 2025 and just 8 in 2024, and it’s the highest since 2016.

“All things considered, it’s not too bad in San Diego, but this is, for us, more than we usually see. This is more human cases than we’ve seen in maybe a decade.” — Allison Bray, County of San Diego Vector Control Program

National data from the Centers for Disease Control and Prevention, current as of Oct. 13, counts six human West Nile disease cases in San Diego County so far in 2026. That’s the most in a single year since 2016, when the county had 20. In every year in between, the county had three cases or fewer. The California Department of Public Health says the state is seeing its highest West Nile activity in five years.

Most people infected with West Nile never feel sick, according to the County’s Health and Human Services Agency. About 1 in 5 develop a fever with symptoms like headache, body aches or rash, and a small number become seriously ill. People over 60 face higher risk. If you’re concerned about symptoms, talk with your health care provider.

Meet the four mosquitoes you’re most likely to run into

Several mosquito species live in San Diego County, but Bray said four are behind most of the bites people notice:

1. Invasive Aedes, the “ankle biters”

Small, black and white, and active during the day. These are the ones biting your ankles while you garden. According to Bray, they’re most active from about July through October, and residents should expect to keep seeing them through at least the end of this month.

2. The southern house mosquito

This is the neighborhood mosquito most people see, and it’s one of the Culex mosquitoes that can spread West Nile virus. Culex mosquitoes are most active around dusk and dawn.

3. A second Culex species

This one prefers marshes, ponds and other natural areas rather than backyard containers. It can also spread West Nile virus.

4. Salt marsh mosquitoes

If you live right on the coast, these may be your biggest annoyance this year. They’re a native species that breeds in salt marshes and bites during the day. “Luckily, those mosquitoes don’t spread any diseases that we know of to people, but they can be really aggressive biters,” Bray said. She added that high, warm tides this year created good conditions for them.

After the storm: your yard checklist

Rachel’s rain left water sitting in plenty of places it doesn’t belong. The National Weather Service recorded a record 0.81 inches at Palomar Mountain on Oct. 12 alone.

Bray’s rule of thumb is simple: “If it’s going to evaporate within a day or two, that’s not a problem. But if anything is staying wet for more than a few days, that’s something they’re going to want to either dump out or maybe add a larvicide that’ll kill the mosquito larvae.”

That matters because, according to the County, mosquitoes can go from egg to biting adult in as little as five days. The invasive ankle biters need very little water to do it. According to Bray, they can lay eggs and grow as larvae in as little as a quarter inch of water.

Walk your property and check these spots:

Illustrations: TrulySD

Keeping them out of the house

Here's the part that surprises people: the ankle biters want to come inside.

"These little ankle biter mosquitoes, they love to bite people. We are their favorite food," Bray said. "These mosquitoes will come inside, like, on purpose."

• Close and check your screens. Keep screens on doors and windows closed, and look for tears or gaps.
• Turn on a fan. These mosquitoes are weak flyers, according to Bray, so moving air can help.
• Keep a fly swatter handy for any that sneak in.

Protecting yourself outdoors

Bray recommends wearing insect repellent in the yard, especially one with an EPA-registered active ingredient. The County lists DEET, picaridin, IR3535, para-menthane-diol, 2-undecanone and oil of lemon eucalyptus. According to Bray, those ingredients have been scientifically evaluated to confirm they repel mosquitoes.

For the ankle biters, Bray said even a little repellent on the ankle area can help a lot, especially before gardening or other yard work.

Long sleeves and pants help too.

When to call the County

If you're dealing with more mosquitoes than you can handle, the County's Vector Control Program will come take a look. That includes apartment properties.

"One of our technicians will come out and they'll be looking for sources of standing water that might be basically the start of the problem," Bray said. They'll also give you advice on keeping standing water out of your yard.

You can also report green swimming pools, high mosquito activity and dead birds such as crows, jays, hawks and owls. The County tests some of those birds for West Nile virus.

Looking for more ways to care for your home? Browse our SD HOME stories and our Around the House guide.