Mosquitoes where you live

The short answer

Which mosquitoes bite you, and which diseases they can carry, depends heavily on where you live and the time of year. There is no single “mosquito problem” across the country. The Northeast and Great Lakes contend with eastern equine encephalitis and La Crosse virus. The Gulf and Southeast carry the heaviest overall biting pressure and the highest chance of local dengue. The western plains see most of their risk from West Nile virus spread by one grassland mosquito. The Southwest and parts of California now host invasive container mosquitoes that were not established there a generation ago.

Two facts hold nationwide. First, West Nile virus is the most commonly reported mosquito-borne disease in the country: in 2023 it accounted for 2,628 of 2,770 reported arboviral disease cases, about 95 percent (1). Second, most people bitten by an infected mosquito never get sick. Roughly 8 in 10 people infected with West Nile virus develop no symptoms, and fewer than 1 percent develop severe neurologic illness (2). The point of knowing your region is not fear. It is knowing which few weeks and which few species actually matter where you are.

Why region matters

Mosquitoes are not one animal with one behavior. Different species breed in different places, feed on different hosts, and carry different viruses. A mosquito that breeds in a shaded backyard tree hole behaves nothing like one that breeds in irrigated grassland or a coastal salt marsh.

Region shapes risk in three linked ways:

• Species. The mosquitoes present in your area determine what can be transmitted at all. Eastern equine encephalitis is maintained by the swamp mosquito Culiseta melanura in freshwater hardwood swamps, so the disease concentrates where those swamps exist (3). La Crosse virus is carried by tree-hole mosquitoes such as Aedes triseriatus, which live in wooded areas east of the Rockies (4). West Nile virus in the drier West is driven largely by Culex tarsalis, a mosquito of rural and irrigated land (5).
• Climate. Temperature and rainfall decide how long mosquitoes are active and how fast a virus can develop inside them. Warm, humid regions support longer seasons and larger populations than cold, dry ones.
• Disease cycle. Most of these viruses live in a bird-and-mosquito or small-mammal-and-mosquito cycle, and people are incidental. Whether that cycle spills over to humans depends on which “bridge” mosquitoes are present and how close people live to the habitat where the cycle runs (3).

The big regional patterns

No region is risk-free, and no region should be treated as uniformly dangerous. These are the broad patterns that surveillance data support. Use them as a starting point, then check your state and county for specifics.

Northeast and Great Lakes: EEE and La Crosse. Eastern equine encephalitis (EEE) transmission is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states and the Great Lakes region (3). EEE is rare, an average of about 11 human cases a year nationwide, but it is one of the most severe mosquito-borne diseases, with roughly a 30 percent case-fatality rate among those who develop brain infection and lasting neurologic effects in about half of survivors (6). La Crosse virus is the leading cause of arboviral encephalitis in children in the country, with about 70 to 80 hospitalized cases a year, concentrated in the upper Midwest and the southern Appalachian region (4).

Gulf and Southeast: heavy burden and dengue potential. This region carries the country’s longest mosquito seasons and heaviest biting pressure, and it is where locally acquired dengue is most likely. Aedes aegypti and Aedes albopictus, the mosquitoes that can transmit dengue, are established across Florida and much of the southern tier (7). During 2024 a record 3,798 dengue cases were reported nationally; about 97 percent were linked to travel, but the small share of locally acquired cases was concentrated here, with Florida reporting 91 (8).

Western plains and Mountain West: West Nile via Culex tarsalis. Across the Great Plains and interior West, most human West Nile risk comes from Culex tarsalis, considered the primary vector to people in the western part of the country (5). This is a mosquito of rural and irrigated landscapes, which is one reason West Nile incidence per person can run high in sparsely populated agricultural states even though total case counts are modest.

Southwest and California: invasive Aedes. Invasive container mosquitoes have expanded across the southern tier. Aedes aegypti has been reported through southern California, Arizona, New Mexico, Texas, Louisiana, and Florida, and established populations in central and southern California have prompted an ongoing public health response (7). These day-biting mosquitoes breed in small artificial containers around homes and are the vectors that make local dengue, and potentially Zika and chikungunya, possible where they take hold.

A regional overview table appears below. For the mosquitoes and diseases specific to your area, see the regional and state pages linked under Explore regions and states.

Season varies by region

When mosquitoes are active also depends on where you live, because most species need warmth to develop and stay active. As a rule, the season is long in the warm south and short in the cold north.

In the Gulf states and the Florida peninsula, mosquito activity can stretch across most of the year, and biting pressure is high for many months. In the upper Midwest, the Northeast, and the northern Mountain West, the active season is compressed into the warm months, often a window of a few months around summer, with a hard stop once temperatures fall. Disease risk usually peaks later than the first bites of spring, because a virus has to build up in the mosquito-and-bird cycle before it spills over to people. In much of the country, that means late summer into early fall is the higher-risk stretch for West Nile virus and EEE, even though mosquitoes are out well before then.

The precise start and end of your local season is best answered by your local mosquito control program or health department, which tracks it directly rather than by a national calendar. Warming trends are lengthening the active season in many places, so historical local dates are a guide, not a guarantee.

How to find your local risk

National patterns tell you what is plausible. Local sources tell you what is actually happening this year. Three places to check:

• Your state health department. States report mosquito-borne disease activity, often with weekly-updated maps of where infected mosquitoes, birds, or human cases have turned up during the season.
• Your county or city health department. Mosquito control is usually handled at the local level. If you are not sure whether your community has a mosquito control district, your local health officials can tell you (9).
• Your local mosquito control district or program. These agencies trap and identify mosquitoes and test them for viruses, so they hold the most current, most local picture of what is biting and what it is carrying (9). The American Mosquito Control Association maintains member lists that can help you locate the program serving your area (10).

When you contact them, useful questions are: which mosquito-borne viruses have been detected locally this season, when the local season typically peaks, and whether any advisories or spraying are in effect.

Sources

1. Centers for Disease Control and Prevention. West Nile Virus and Other Nationally Notifiable Arboviral Diseases, United States, 2023 (MMWR). West Nile virus was the most commonly reported arboviral disease, 2,628 of 2,770 cases, about 95 percent. https://www.cdc.gov/mmwr/volumes/74/wr/mm7421a1.htm (accessed 2026-07-20).
2. Centers for Disease Control and Prevention. Symptoms of West Nile. About 8 in 10 infected people have no symptoms; fewer than 1 percent develop severe neurologic illness. https://www.cdc.gov/west-nile-virus/signs-symptoms/index.html (accessed 2026-07-20).
3. Centers for Disease Control and Prevention. Transmission of Eastern Equine Encephalitis Virus. Maintained by Culiseta melanura in freshwater hardwood swamps of Atlantic and Gulf Coast states and the Great Lakes region; bridge mosquitoes transmit to people. https://www.cdc.gov/eastern-equine-encephalitis/php/transmission/index.html (accessed 2026-07-20).
4. Centers for Disease Control and Prevention. About La Crosse Virus. Leading cause of arboviral encephalitis in children, about 70 to 80 hospitalized cases per year, upper Midwest and southern Appalachia; vector Aedes triseriatus. https://www.cdc.gov/la-crosse-encephalitis/about/index.html (accessed 2026-07-20).
5. Dunphy BM, et al. Long-term surveillance defines spatial and temporal patterns implicating Culex tarsalis as the primary vector of West Nile virus (peer-reviewed; PMC). Culex tarsalis is the primary vector to people in the western part of the country. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6488619/ (accessed 2026-07-20).
6. Centers for Disease Control and Prevention. About Eastern Equine Encephalitis Virus. Average of about 11 human cases per year; roughly 30 percent case-fatality in neuroinvasive disease, with lasting effects in about half of survivors. https://www.cdc.gov/eastern-equine-encephalitis/about/index.html (accessed 2026-07-20).
7. Centers for Disease Control and Prevention. Potential Range of Aedes Mosquitoes. Aedes aegypti and Aedes albopictus reported across the southern tier, including southern California, Arizona, New Mexico, Texas, Louisiana, and Florida. https://www.cdc.gov/mosquitoes/php/toolkit/potential-range-of-aedes.html (accessed 2026-07-20).
8. Centers for Disease Control and Prevention. Increase in Travel-Associated and Locally Acquired Dengue Cases, United States, 2024 (MMWR). Record 3,798 cases; 97.2 percent travel-associated, 2.8 percent locally acquired; local cases in Florida (91), California (18), Texas (1). https://www.cdc.gov/mmwr/volumes/75/wr/mm7518a1.htm (accessed 2026-07-20; page returned HTTP 403, figures from CDC search result text for the same URL).
9. Centers for Disease Control and Prevention. Mosquito Control in a Community. Mosquito control is usually handled locally; contact local health officials or your mosquito control district. https://www.cdc.gov/mosquitoes/mosquito-control/mosquito-control-in-a-community.html (accessed 2026-07-20).
10. American Mosquito Control Association. Mosquito Control. Member and control-program resources for locating the program serving your area. https://www.mosquito.org/mosquito-control/ (accessed 2026-07-20).

Explore regions and states

• Northeast and Great Lakes region [link placeholder]
• Gulf and Southeast region [link placeholder]
• Western plains and Mountain West region [link placeholder]
• Southwest and California region [link placeholder]
• State-by-state index [link placeholder]
• Find your local mosquito control district [link placeholder]

Educational note: This page is a general reference and is not medical advice. It does not diagnose illness or replace guidance from your health department or a clinician. If you have symptoms after mosquito bites, contact a healthcare provider. For the most current local conditions, check your state and county health departments and your local mosquito control program.

Last reviewed 20 July 2026.