Culex Mosquito
Culex mosquitoes are plain brown mosquitoes that bite from dusk to dawn and lay floating rafts of eggs on still, nutrient-rich water such as storm drains, ditches and neglected pools. In South Florida the most important are the southern house mosquito (Culex quinquefasciatus), found in all 67 Florida counties, and the Florida SLE mosquito (Culex nigripalpus), both of which can carry West Nile and St. Louis encephalitis viruses.
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What Are Culex Mosquitoes?
Culex is a large genus of mosquitoes found around the world. The CDC lists three main Culex species in the United States: Culex quinquefasciatus, Culex pipiens and Culex tarsalis. Of these, the southern house mosquito is the one that is found throughout Florida. Culex pipiens, the northern house mosquito, usually is not found south of about 39° north latitude, far north of Florida. For an overview of all the mosquitoes in our area, see mosquitoes in South Florida.
The Culex species that South Florida homeowners should know are:
- Southern house mosquito (Culex quinquefasciatus): found in all 67 Florida counties, including the Keys. It breeds in water around homes, storm drains and wastewater, and it is the classic nighttime biter. UF/IFAS calls it the principal vector of St. Louis encephalitis virus in the southern United States.
- Florida SLE mosquito (Culex nigripalpus): also found in all 67 counties and most abundant in the central and southern peninsula, from Brevard County south to Miami-Dade and west to Collier. UF/IFAS identifies it as the primary vector of St. Louis encephalitis virus in the southern half of Florida and one of the most important vectors of West Nile virus in the state.
- Culex lactator: a tropical species that UF/IFAS researchers first found in Miami-Dade County in 2018. It has established populations in Miami-Dade, Collier and Lee counties, and its disease risk has not yet been well studied.
- Frog-biting Culex (such as Culex territans): live in freshwater wetlands and feed mainly on frogs and reptiles, only occasionally biting people.
South Florida’s climate gives Culex plenty of habitat: thousands of storm drains and catch basins, canals, lakes and retention ponds, roadside ditches and wastewater areas. The rainy season from May through October floods low ground and ditches, and in warm weather a new generation can develop in about a week.
How to Identify Culex Mosquitoes
UF/IFAS describes the southern house mosquito as a “medium-sized brown mosquito,” about 3.96 to 4.25 millimeters long:
- Color: brown, with a darker proboscis, thorax, wings and legs.
- Abdomen: pale bands at the base of each abdominal segment.
- No white markings on the back: unlike Aedes, it has no lyre or white stripe, and its legs are not banded.
- Males: feed only on plant sugars and do not bite.
- Larvae: have a long breathing tube (siphon), about four times longer than it is wide; pupae are comma-shaped.
Culex vs. Aedes: Aedes aegypti and the Asian tiger mosquito are black and white with banded legs and bite during the day. If you are bitten after sunset or during the night by a plain brown mosquito, it is likely a Culex.
Culex vs. midges: non-biting midges also swarm near lakes and ponds at dusk, but they do not bite, and their wings are shorter than their bodies.
Life Cycle and Behavior
- Egg rafts: instead of laying single eggs on dry surfaces like Aedes, Culex females lay their eggs one at a time but stick them together into a floating raft. The CDC says a raft holds 100 to 300 eggs; UF/IFAS reports that a southern house mosquito female can lay up to five rafts in her lifetime, and Culex nigripalpus rafts hold about 90 to 210 eggs.
- Hatching: eggs of the southern house mosquito hatch 24 to 30 hours after they are laid, and Culex nigripalpus eggs in 24 to 36 hours. Unlike Aedes eggs, they cannot wait for months in a dry container.
- Larvae: the wigglers live in the water, feed on organic material and develop in about five to eight days in warm water (30°C, or 86°F).
- Pupae: adults emerge after about 36 hours at 27°C (about 81°F).
- Adults: the CDC estimates the full cycle from egg to adult takes about 7 to 10 days.
The CDC notes that adult Culex are most active from dusk to dawn and rest during the day in grass, shrubs and other thick vegetation that is cool, dark and humid. UF/IFAS reports that southern house mosquito females fly at night to lay eggs and feed throughout the night on mammals and/or birds. Culex nigripalpus feeds mainly in the twilight periods around sunrise and sunset; in Florida’s dry winter and spring it bites mostly birds, and in the wet summer and fall it shifts to mammals, including people, dogs and horses. A UF/IFAS study that included mosquitoes from Miami-Dade found that brown anoles, the small lizards seen on South Florida sidewalks, were its most frequent host.
Rain drives Culex nigripalpus populations. During long droughts, females carrying mature eggs build up. When about 2 inches or more of rain falls in 24 hours and floods ditches, they lay eggs and look for hosts at the same time.
Signs of a Culex Mosquito Problem
- Mosquito bites in the evening and during the night rather than in the middle of the day.
- Plain brown mosquitoes without white markings.
- Small floating rafts of eggs on the surface of still water in a fountain, bucket, birdbath or neglected pool.
- Wigglers in storm drains, catch basins, ditches or green pool water.
- A jump in nighttime mosquitoes a week or so after a heavy rain floods ditches and low spots.
- Mosquitoes coming from shaded hedges and dense ground cover at dusk.
Why Culex Mosquitoes Are a Problem
Nighttime bites interrupt sleep and make evening time outside uncomfortable, but the main concern is disease. In the United States, the CDC says Culex mosquitoes can spread West Nile, St. Louis encephalitis and eastern equine encephalitis viruses.
These viruses circulate mainly between wild birds and Culex mosquitoes, and only occasionally infect people and horses. People are “dead-end” hosts: a mosquito that bites an infected person does not pick up the virus. In Florida, UF/IFAS considers the southern house mosquito the principal St. Louis encephalitis vector in the southern U.S., but not the likely primary vector of West Nile virus in Florida, though it can help maintain the virus in birds and can transmit it to people. Culex nigripalpus is the primary St. Louis encephalitis vector in the southern half of the state. Florida had St. Louis encephalitis epidemics in 1959, 1961, 1962, 1977 and 1990.
Today, human cases are uncommon, and the Florida Department of Health publishes weekly arbovirus surveillance reports that track West Nile and St. Louis encephalitis activity across the state. County mosquito control programs keep watch with traps and surveillance, and reducing breeding sites helps keep it that way. Outside the United States, the southern house mosquito also transmits the parasite that causes lymphatic filariasis.
Where Culex Mosquitoes Hide in South Florida Homes and Businesses
UF/IFAS describes the southern house mosquito’s larval habitat as nutrient-rich standing water, ranging from wastewater to birdbaths and old tires. Look for:
- Storm drains and catch basins in driveways, parking lots and streets, one of the largest man-made sources.
- Drainage ditches and swales that hold water after rain, especially if blocked by debris.
- Neglected swimming pools and hot tubs, fountains and ornamental ponds without fish or circulation.
- Wastewater areas, where nutrient-rich water collects.
- Containers: buckets, tires, planters, toys, birdbaths and flower pots.
- Lake and canal edges with thick vegetation and still water.
Adults rest in grass, shrubs and dense vegetation during the day and become active at dusk. Restaurants, hotels, warehouses and apartment complexes with many drains, catch basins and landscaped retention areas offer plenty of the water Culex prefers. If clogged drains are holding water on your property, our drain cleaning service can help along with mosquito treatment.
When Culex Mosquitoes Are Most Active in South Florida
| Season | Culex activity | What to do |
|---|---|---|
| December to February (dry season) | Lower activity; mosquitoes slow down near 60°F and stop flying around 50°F, but drains, ponds and pools still hold water during warm spells. Culex nigripalpus feeds mostly on birds. | Clean out drains and ditches and keep pools circulating. |
| March to May | Numbers start to rise with warmer nights; in droughts, Culex nigripalpus females wait for rain. | Check birdbaths, fountains and containers weekly. |
| June to September (peak rainy season) | Peak populations; heavy rains flood ditches and trigger synchronized egg laying and biting. | Clear standing water within days of each storm and protect yourself at dusk. |
| October to November | Still active; storm debris and blocked drains hold water after hurricanes. | Clear debris from drains and swales and inspect the yard after heavy rain. |
How to Prevent Culex Mosquitoes
The Florida Department of Health’s Drain and Cover routine works against Culex as well:
- Drain water from buckets, toys, tarps, flower pots and trash cans at least once a week, and get rid of old tires.
- Keep pools chlorinated and in good condition, and empty plastic pools when not in use.
- Clear gutters and drainage ditches of debris so water keeps flowing.
- Change birdbath water every two or three days, as UF/IFAS suggests, and clean pet bowls.
- Treat water you can’t drain, such as an ornamental pond or fountain, with a Bti product (look for the israelensis strain) or stock small ponds with gambusia mosquito fish, following UF/IFAS guidance.
- Cover skin in the evening with long sleeves and pants and use a repellent containing DEET, picaridin, oil of lemon eucalyptus or IR3535, following the label.
- Cover doors and windows with screens and repair holes, since Culex bites at night when windows may be open.
County programs also handle Culex sources on public property, such as storm drains and ditches. Report problems to Miami-Dade Mosquito Control or Broward County Mosquito Control through 311, Palm Beach County at 561-967-6480 or the Florida Keys Mosquito Control District in Monroe County.
How Toro Gets Rid of Culex Mosquitoes
- Water-source inspectionA Toro technician checks drains, catch basins, ditches, pools, fountains, ponds and containers on your property, and the dense vegetation where adults rest during the day.
- Identify the mosquitoWe confirm whether nighttime biting is coming from Culex and look for egg rafts and larvae to locate the exact source.
- Targeted mosquito treatmentOur mosquito treatment targets breeding water and resting areas on your property, applied according to label directions.
- Follow-up after the rainsCulex numbers jump after heavy rain, so regular visits through the rainy season keep them down. Our 110% Satisfaction Guarantee means that if the bugs come back, so will Toro, at no additional cost to you.
Toro Pest Management has protected South Florida homes and businesses since 1969, with service in Miami, Hialeah, Fort Lauderdale and Key West. We respond within 24 hours, guaranteed, and offer a free inspection with $25 off your first service. Call 305-594-4767. Hablamos Español.
Seeing signs of culex mosquito (southern house mosquito)? Get a free inspection and $25 off your first service.
Schedule Your Free InspectionCulex mosquito (southern house mosquito): Frequently Asked Questions
What does a Culex mosquito look like?
The southern house mosquito is a medium-sized brown mosquito about 4 millimeters long. Its proboscis, thorax, wings and legs are darker than the rest of the body, and the abdomen has pale bands at the base of each segment. It has no white stripes or lyre pattern on its back and no banded legs, which separates it from Aedes aegypti and the Asian tiger mosquito.
When do Culex mosquitoes bite?
Culex mosquitoes are most active from dusk to dawn. UF/IFAS reports that southern house mosquito females fly at night to lay eggs and feed throughout the night, which is why they are the mosquitoes that bother you after dark. The Florida SLE mosquito, Culex nigripalpus, feeds mainly around sunset and before sunrise. During the day, Culex adults rest in cool, shaded vegetation.
Do Culex mosquitoes carry West Nile virus in Florida?
They can. Culex mosquitoes spread West Nile and St. Louis encephalitis viruses, which circulate mainly between birds and mosquitoes and only occasionally infect people and horses. UF/IFAS names Culex nigripalpus one of the most important vectors of both viruses in Florida. Human cases in Florida are uncommon, and the Florida Department of Health tracks them in its weekly arbovirus surveillance reports.
Where do Culex mosquitoes breed?
Culex females lay rafts of eggs on the surface of standing water, often water rich in organic matter. Around South Florida homes and businesses, common sources are storm drains and catch basins, drainage ditches, wastewater areas, neglected swimming pools, ponds and lake edges, fountains, birdbaths, old tires and buckets. Culex nigripalpus also breeds in shallow roadside ditches flooded by heavy rain.
What is the difference between Culex and Aedes mosquitoes?
Aedes aegypti and the Asian tiger mosquito are black and white, bite during the day and lay single eggs on container walls that can survive dry for months. Culex mosquitoes are brown, bite from dusk to dawn and lay floating egg rafts directly on the water. Aedes are linked with dengue, Zika and chikungunya, while Culex are linked with West Nile and St. Louis encephalitis viruses.
Why do Culex mosquitoes increase after heavy rain?
Rain floods ditches, low ground and drains, creating new places to lay eggs. UF/IFAS explains that during droughts Culex nigripalpus females hold their eggs, and when about 2 inches or more of rain falls in 24 hours and floods ditches, they lay eggs and seek hosts in a synchronized wave. With eggs hatching in about a day and adults in about a week, numbers can climb quickly in summer.
How do I get rid of Culex mosquitoes around my house?
Start with the water. Keep pools chlorinated and circulating, clear debris from ditches and gutters so water flows, empty birdbaths and buckets weekly and treat water you cannot drain, such as an ornamental pond, with a Bti product or mosquito fish, following UF/IFAS guidance. Screens keep nighttime biters out. A professional inspection can find hidden sources like catch basins and help treat resting areas.
Related Pests
Pest Control Across South Florida
Toro treats culex mosquito (southern house mosquito) in homes and businesses throughout Miami-Dade, Broward and Palm Beach counties, including:
- Miami
- Hialeah
- Doral
- Miami Beach
- Coral Gables
- Homestead
- Fort Lauderdale
- Hollywood
- Pembroke Pines
- Miramar
- Boca Raton
- West Palm Beach
Last updated: October 29, 2026
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If the bugs come back, so will TORO at no additional cost to you. TORO will respond with in 24 hours Guaranteed. Our technician will arrive quickly and deal with the pest problem to prevent recurrence.
