Mosquitoes in the San Gabriel Valley
The SGV's mosquito story changed when the daytime ankle-biters arrived. Here's what's biting, the standing water behind it, and the free help most residents don't know exists.
- Daytime biting around ankles = invasive Aedes mosquitoes
- Native Culex mosquitoes bite at dusk and night
- They breed in tiny amounts of standing water — a bottle cap is enough
- Itchy welts, often several in a cluster
- Peak season roughly April through October
What they look like
The mosquito picture in the San Gabriel Valley changed around a decade ago when invasive Aedes mosquitoes — small, black-and-white striped “ankle biters” — established here. Unlike our native Culex mosquitoes, which bite around dusk, Aedes bite aggressively during the day, usually low on the legs and ankles.
Both are more than a nuisance: Culex can carry West Nile virus, which is why mosquito control in California is taken seriously enough to have its own public agencies.
Mosquitoes fast facts
| Feature | Detail |
|---|---|
| Looks like | Small; Aedes are black with white stripes |
| Where found | Anywhere with standing water nearby |
| What they do | Itchy bites; can carry disease |
| Active when | Aedes by day, Culex at dusk; Apr–Oct peak |
| Concern level | Real — bites plus disease potential |
Where they live
Mosquitoes don't travel far from where they hatch — invasive Aedes often stay within a couple hundred feet. If you're getting bitten in your yard, the breeding water is usually on your property or a neighbor's: plant saucers, buckets, clogged gutters, fountains that stopped running, trash-can lids, even a bottle cap. They need only a spoonful of water and about a week.
That's why fogging a yard rarely fixes anything for long — the source keeps producing new mosquitoes every few days.
Signs of a problem
Getting bitten during the day around the ankles and lower legs is the classic invasive-Aedes sign. Clusters of itchy welts after time in the yard, mosquitoes resting on shaded walls, and wrigglers (larvae) in any standing water are the others.
If bites happen mostly at dusk instead, that points to native Culex — same fix: find and dump the water.
Do mosquito coils work, and are they harmful?
Mosquito coils can cut bites in field tests, but the outdoor evidence is thin, they have not been shown to prevent mosquito-borne disease, and the smoke is a real concern: a study in Environmental Health Perspectives measured fine particles from one burning coil equal to 75 to 137 cigarettes.
That 2003 study, by Liu and colleagues, tested coils sold in China and Malaysia and also found formaldehyde from one coil equal to about 51 cigarettes; the authors concluded the smoke could pose significant acute and chronic health risks. On the other side, field trials, including a 2018 study of outdoor-biting mosquitoes in Laos, found coils cut bites, while their authors noted there is not enough evidence that coils prevent disease. The practical reading: if you burn one, do it outdoors with plenty of air, never in a closed room, and rely on repellent on your skin for real protection.
How to get rid of mosquitoes in your yard: what works
To get rid of mosquitoes in your yard, empty every container that holds water once a week and protect your skin with an EPA-registered repellent. Invasive Aedes mosquitoes breed in a spoonful of water and stay close to where they hatch, so the source is almost always on your property or the one next door.
| Method | Evidence | Verdict |
|---|---|---|
| Dump and scrub standing water weekly | Removes the larvae before they become biting adults; Aedes eggs stick to container walls, so scrub saucers and buckets | The single most effective step |
| EPA-registered skin repellent | The EPA lists DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol and 2-undecanone as registered active ingredients | Works where you are; reapply by the label |
| Window and door screens | Keeps biting adults out of the house | Works; repair tears |
| Mosquito coils | Some bite reduction in field tests; heavy fine-particle smoke (Liu and colleagues, 2003) | Outdoors only, and second to repellent |
| Citronella candles and bug zappers | Citronella gives brief, localized relief at best; zappers mostly kill harmless insects | Not meaningful |
| Ultrasonic devices and apps | A Cochrane review found electronic repellents do not prevent bites | Do not work |
| Yard fogging | Kills adults present that day; breeding water keeps producing more | Temporary |
Free mosquito help: the San Gabriel Valley Mosquito and Vector Control District
The San Gabriel Valley Mosquito and Vector Control District serves 26 cities and more than 1.5 million residents. You can request a property consultation or submit a mosquito tip on its website, ask about mosquito fish for ponds, and follow its newer programs against invasive Aedes, including a sterile insect technique program that releases sterilized male mosquitoes. Call (626) 814-9466. Routine mosquito abatement is not an ExterMetro service, and in the San Gabriel Valley you already pay for an agency that does it: the district responds to mosquito problems, inspects sources and treats them at no charge. Most residents have never heard of it, and it is the single most effective call you can make. While we are treating your property for other pests, we will point out breeding water when we see it, and if what is biting you turns out to be fleas, that one is ours.
Sources
- UC IPM Pest Notes: Mosquitoes (University of California)
- San Gabriel Valley Mosquito & Vector Control District
- Liu and colleagues, Mosquito coil emissions and health implications, Environmental Health Perspectives (2003)
- Field evaluation of personal protection methods against outdoor-biting mosquitoes in Lao PDR, Parasites & Vectors (2018)
- EPA: Find the Insect Repellent That Is Right for You
- Cochrane review: Electronic mosquito repellents for preventing mosquito bites and malaria infection (Enayati, Hemingway and Garner, 2007)
Related Pests
Quick Answers
Quick Answers.
Why am I getting mosquito bites during the day?
That's the calling card of invasive Aedes mosquitoes — the black-and-white 'ankle biters' established in the SGV over the last decade. They bite by day, usually low on the legs, and breed in tiny containers of water within a couple hundred feet of where they bite.
Does ExterMetro treat mosquitoes?
Routine mosquito abatement isn't one of our services — and honestly, you already have a better option: the San Gabriel Valley Mosquito & Vector Control District handles mosquito problems for residents free. We'll point out breeding water we spot during any service, and if the biting turns out to be fleas, that's our job.
What is the SGV Mosquito & Vector Control District?
A public agency, funded by property assessments, that inspects and treats mosquito sources across the San Gabriel Valley at no charge — including backyard problems and green pools. Requests go through sgvmosquito.org. It's the most effective mosquito call most residents never make.
How do I find where mosquitoes are breeding?
Walk the yard after watering or rain and look for anything holding water for a week or more: plant saucers, buckets, toys, clogged gutters, dead fountains, drain pans. Aedes need only a spoonful. Dump, scrub and flip — scrubbing matters because their eggs glue to container walls.
Are mosquitoes in the SGV actually dangerous?
They can be. Native Culex mosquitoes are the local West Nile virus carriers, and invasive Aedes are capable of spreading other viruses. Most bites are just itchy — but it's why mosquito control here has its own public agency, and why standing water is worth taking seriously.
Do bug zappers or citronella candles work?
Not meaningfully. Zappers mostly kill harmless insects, and citronella gives brief, localized easing at best. Finding and dumping the breeding water — and calling the district for what you can't reach — is what actually drops the numbers.
Is it a mosquito or a fungus gnat?
Fungus gnats look like tiny mosquitoes, with long legs and antennae, but they do not bite, and they drift around houseplants and windows instead of landing on you. If the “mosquitoes” are indoors near potted plants and nobody is getting bitten, they are almost certainly fungus gnats breeding in wet potting soil. Here is how to get rid of fungus gnats.
Do mosquito coils work?
Partly. Field trials show coils can cut bites outdoors, but the outdoor evidence is limited and there is not enough evidence that coils prevent mosquito-borne disease. Repellent on your skin and dumping standing water do more.
Are mosquito coils harmful to breathe?
The smoke is a real concern. A 2003 study in Environmental Health Perspectives found one burning coil released fine particles equal to 75 to 137 cigarettes and formaldehyde equal to about 51, and its authors warned of acute and chronic health risks. Never burn one in a closed room.
What is the best mosquito repellent?
One registered with the EPA, used by the label. The EPA lists DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol and 2-undecanone as registered repellent ingredients, and its online tool helps you pick by protection time.
How do I get rid of mosquitoes in my yard?
Walk the yard once a week and dump and scrub anything holding water: saucers, buckets, toys, gutters, tarps, even a bottle cap. Invasive Aedes stay within a couple hundred feet of where they hatch, so the source is close. For a green pool or water you cannot reach, call the San Gabriel Valley Mosquito and Vector Control District.
Do mosquito repellent apps or ultrasonic devices work?
No. A Cochrane systematic review of electronic mosquito repellents found they do not prevent bites. Spend the money on an EPA-registered repellent.
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