Aedes aegypti on the West Coast: identification and risk in 2026

Updated on: June 24, 2026

Quick overview

• Two invasive Aedes mosquito species are now established across California and the wider West Coast
• Both species bite during the day, not just at dusk
• They breed in tiny amounts of standing water
• Both can spread dengue fever, Zika virus, chikungunya, and yellow fever
• If you're being bitten in your yard, the breeding source is likely on or near your property.

Jump to

What are invasive Aedes mosquitoes?

How to identify yellow fever mosquitoes vs. Asian tiger mosquitoes

The dangers of Aedes mosquitoes

Identifying and treating Aedes mosquito bites

Cycle of mosquito-borne disease 

How to protect your family and home

What kills Aedes mosquitoes?

People have been spending more time than ever at home lately, but that hasn’t hindered mosquito populations. Two non-indigenous, disease-carrying species of the invasive Aedes genus were reported in Southern California: Aedes albopictus and Aedes aegypti. The California Department of Public Health (CDPH) released a map of confirmed sightings, but these species have now expanded into other states on the West Coast. 

These “exotic” mosquitoes are nothing new to eastern states, but they’ve made their way to western states likely through travel, trade, and climate change. Fortunately, mosquitoes can’t spread Coronavirus (COVID-19), but the Aedes genus is responsible for transmitting Zika, West Nile virus, dengue virus, chikungunya virus, yellow fever virus, and parasitic canine heartworm.

What are invasive Aedes mosquitoes?

California has traditionally been home to mild-mannered mosquitoes. However, these two species are aggressive day-feeders. They both possess bold, black and white stripes, which is key to early detection. Unlike the common mosquitoes most people are used to, invasive Aedes species are aggressive daytime biters. 

They don't wait until dusk; they'll bite throughout the day, often targeting ankles and lower legs. They also breed in very small amounts of standing water, which makes them harder to control than species that rely on larger water sources.

How to identify yellow fever mosquitoes vs. Asian tiger mosquitoes

Both the yellow fever mosquito and the Asian tiger mosquito are invasive species now established across much of California and the wider West Coast. They look similar at first glance, but there are clear differences once you know what to look for. Getting the ID right matters because these two species behave differently and pose different levels of risk.

Yellow fever mosquito identification

The yellow fever mosquito is small, roughly ¼ inch long, and has a striking black-and-white pattern. The most distinctive feature is a white, lyre-shaped marking on the upper part of its thorax, which looks a bit like a violin or a pair of curved brackets. Its legs are banded in black and white.

Of the two species, the yellow fever mosquito is more dangerous and bothersome to humans. Not only are we their preferred host, but they inhabit areas where people congregate and bite them repeatedly. This easy access to blood meals, paired with back-to-back bites, makes the re-introduction of tropical mosquito-borne illness in the US a potential threat. Aedes aegypti are native to tropical and subtropical regions like South America, but have been known to inhabit temperate territories as well.

Asian tiger mosquito identification

The Asian tiger mosquito is similar in size to the yellow fever mosquito and also has black-and-white banding on its legs. The key visual difference is a single, bold white stripe running straight down the center of its thorax, rather than the lyre-shaped marking of the yellow fever mosquito.

This species is striped and endemic to Asia, hence its nickname. Aedes albopictus are opportunistic day-biters that feed on a variety of hosts, not just humans. While the Asian tiger mosquito is less threatening, they’re still vectors of 30 different viruses, with dengue being the most prevalent in humans.

Key differences: invasive vs. native West Coast mosquitoes

If you're used to being bitten at dusk by mosquitoes near a pond or creek, these invasive species will feel very different. Here's how they compare to the native mosquitoes most Californians are familiar with:

• Biting time: Invasive mosquitoes tend to bite during the day, while native mosquitoes are most active at dusk and dawn.
• Preferred host: The yellow fever mosquito feeds almost exclusively on humans, whereas native mosquitoes feed on both humans and birds.
• Breeding sites: Invasive species breed in tiny containers, even as small as a bottle cap. Native mosquitoes need larger bodies of standing water.
• Flight range: Invasive mosquitoes have a short range of around 150 to 200 yards, meaning the source is usually close by. Native mosquitoes travel much farther.
• Key diseases: Invasive species can spread dengue, Zika, chikungunya, and yellow fever. Native mosquitoes are the primary vector for West Nile virus.
• Markings: The yellow fever mosquito has a lyre-shaped white marking on its thorax, the Asian tiger mosquito has a single white stripe, and native mosquitoes are plain brown or gray with no bold markings.

The short flight range of these invasive mosquitoes is actually an important clue. If you're being bitten in your yard during the day, the breeding source is almost certainly within your own property or a neighbor's.

Are these mosquitoes dangerous?

The short answer is yes, the invasive Aedes mosquitoes are considered dangerous because they can spread several serious illnesses. They are the primary carriers of viruses like dengue fever, Zika virus, chikungunya, and yellow fever.

Not every bite from an Aedes mosquito will lead to illness, but the risk is there, especially in areas where these viruses are active. That’s why it’s important to reduce exposure and control mosquito activity around your home. Our pest control experts can help with this.

The 2024 to 2025 local dengue outbreaks in Southern California

In the summer and fall of 2024, Los Angeles County recorded 14 locally acquired dengue cases, meaning people who had not traveled internationally were infected right here in Southern California. 

According to a study published in Emerging Infectious Diseases by the CDC and the LA County Department of Public Health, eight of those cases were concentrated in a single San Gabriel Valley neighborhood, with evidence of sustained local transmission over a seven-week period. Six of the 14 patients required hospitalization.

This was not a one-off event: The CDC confirmed that local dengue transmission occurred in California, Florida, and Texas in 2024, part of a year in which over 12 million dengue cases were reported across the Americas. 

Travel-associated dengue cases in LA County alone jumped from 75 in 2023 to 222 in 2024, creating more opportunities for the virus to reach local mosquito populations. 

By 2025, the threat had not gone away. The San Gabriel Valley Mosquito and Vector Control District reported the first locally acquired dengue case of the 2025 mosquito season in October.

Zika, West Nile, and heartworm risks

Not all mosquitoes carry the same diseases, and the invasive species now spreading across California pose different risks than the native ones most people are used to.

Zika virus is primarily spread by yellow fever mosquitoes. In most healthy adults, symptoms are mild or absent. The bigger concern is for pregnant women, as Zika infection during pregnancy has been linked to serious birth defects.

West Nile virus is spread by native mosquito species, not the invasive ones. Most people who contract it have no symptoms. In rare cases, it can cause serious neurological complications.

Heartworm is a risk that often gets overlooked. Mosquitoes can transmit heartworm larvae to dogs and cats, and left untreated, it can cause life-threatening damage to a pet's heart and lungs. Year-round prevention from your vet is the best protection, but reducing mosquito populations around your home helps too.

Identifying and treating Aedes mosquito bites

Knowing what to look for after a bite from one of these invasive mosquitoes can help you respond quickly and appropriately. Here's what to expect and when to take action.

What does an Aedes mosquito bite look like?

An Aedes mosquito bite looks much like a typical mosquito bite: small, red, and itchy. The area may become swollen or irritated, especially if you scratch it. People who are sensitive to mosquito bites may notice larger welts or more intense itching.

What to do if you experience symptoms after a bite

Most mosquito bites are just an irritation, but it's worth knowing when to take them more seriously, especially given the disease risks these invasive species can carry.

If you develop a fever, rash, joint pain, headache, or feel generally unwell in the days following a bite, don't brush it off. These can be early signs of a mosquito-borne illness. Please seek advice from a healthcare professional if you experience any of these symptoms, and let them know about the bite and when it occurred. The same applies to pets. If your dog or cat seems lethargic, has difficulty breathing, or shows other unusual symptoms after time outdoors, contact your vet.

Cycle of mosquito-borne disease

In order for an outbreak to occur, the following steps must take place:

• A person becomes infected with a virus
• A mosquito then feeds on the infected person (during the first week following exposure), transmitting the virus to the mosquito
• The infected mosquito then feeds on healthy hosts, spreading disease further
• The cycle repeats many times, becoming an outbreak

Once a mosquito becomes infected, it is capable of spreading dangerous pathogens to subsequent hosts for the rest of its life. Since there are no vaccines or medicinal cure for most mosquito-borne viruses, prevention is essential.

How to protect your family and home

There’s no simple solution to eradicating mosquitoes, but following these prevention tips will make a big difference.

Remove standing water

Mosquitoes need water to breed, and they don't need much. Even a bottle cap of water is enough. To prevent them:

• Empty out birdbaths, plant saucers, buckets, and any containers that collect rainwater
• Check for low spots in your yard where puddles tend to form after rain.

Repair broken screens

Torn or ill-fitting window and door screens are one of the most common ways mosquitoes get inside, so:

• Check screens regularly, especially at the start of warmer months
• Use door sweeps to close gaps at the base of exterior doors.

Clean out gutters of debris

Clogged gutters trap water and create ideal breeding conditions for mosquitoes. Make sure to:

• Clear them out at least twice a year, and more often if you have trees nearby
• Make sure downspouts are directing water away from the foundation.

Keep your yard clean

Overgrown grass, leaf piles, and dense shrubs provide shaded spots for mosquitoes to rest during the day. In the warmer months, ensure you’re:

• Keeping grass trimmed and removing yard debris regularly
• Moving outdoor furniture away from thick vegetation where possible.

Wear insect repellent

When spending time outside, use a repellent that works for you. Products containing DEET are widely used and effective. Reapply as directed, especially if you're sweating or spending extended time outdoors, and cover up with long sleeves and light-colored clothing when mosquitoes are active.

What kills Aedes mosquitoes?

Effectively killing these invasive mosquitoes requires targeting both adult mosquitoes and their breeding sites. Adult mosquitoes can be treated using products applied by a technician as part of a professional mosquito control service. These treatments are placed in shaded areas and sheltered spots where Aedes mosquitoes tend to rest during the day.

The most effective way to reduce mosquito numbers around your home or business is to combine targeted treatments, regular inspections, and source reduction, targeting the pests at all stages of their life cycle - egg, larva, and adult.

Call a professional today

Mosquitoes are more than a backyard nuisance. If you're seeing more of them than usual, it's worth getting a professional to take a look. Our mosquito control services help reduce mosquito activity and protect your outdoor spaces.