Mosquitoes

Mosquitoes are small, long-legged flies whose females drink blood to produce eggs and lay them on or near standing water. In the US they are mainly a nuisance, but a few species carry West Nile virus, eastern equine encephalitis and, in the South, dengue, and they spread heartworm to dogs and cats.

This page is the biology: how long they live, when they show up and leave, and what each species does differently. For control, go to how to get rid of mosquitoes; for itchy welts, see mosquito bites.

What mosquitoes look like

• Body: slender, 1/8 to 3/8 inch, with scales on the wings and body.
• Mouthparts: a long, straight proboscis sticking forward from the head. This is the quickest way to tell a mosquito from a midge.
• Antennae: bushy and feathery in males, thin and lightly haired in females.
• Resting posture: Culex and Aedes rest with the body parallel to the surface; Anopheles rest with the tail tipped up at an angle.

Look-alikes that do not bite: crane flies ("mosquito hawks", much larger with fragile legs that fall off), non-biting midges (no proboscis, gather in clouds over lakes) and fungus gnats (tiny, dark, around houseplants; see fungus gnats). If you see a cloud of tiny insects indoors near soil, it is almost certainly gnats, not mosquitoes.

Types of mosquitoes in the US

Over 3,700 mosquito species exist worldwide (CDC); about 200 occur in the United States, but a handful cause most of the biting:

"Iceland mosquitoes" is a common search because Iceland had no mosquitoes until October 2025, when three Culiseta annulata were caught at Kjós, north of Reykjavík, probably arrived by freight. The US has no such luck: every state has them, including Alaska, which has some of the densest summer swarms anywhere.

Life cycle and how long mosquitoes live

Mosquitoes go through four stages: egg, larva, pupa, adult. The first three need water.

1. Eggs. Culex lay floating rafts of 100 to 300 eggs on the water surface. Aedes glue single eggs just above the waterline inside containers, where they can survive dry for months.
2. Larvae ("wigglers") hang from the surface and breathe through a tube, eating bacteria and algae. 5 to 10 days in warm weather.
3. Pupae ("tumblers") do not eat. 1 to 3 days.
4. Adults emerge on the water surface.

From egg to biting adult takes about a week, sometimes less, in summer heat (UC IPM). Aedes eggs laid on damp surfaces can wait months or even years for water. That is why emptying containers once a week breaks the cycle. The CDC puts adult life at about 2 to 4 weeks depending on species, temperature and humidity, with females outliving males, long enough to lay several batches of eggs.

What mosquitoes eat

Both sexes feed on flower nectar, fruit juice and plant sap for energy. Only the female takes blood, and only because she needs the protein to develop eggs. Males never bite. A female can drink up to three times her weight in blood, then rests for two or three days to digest it before laying.

Different species prefer different hosts: Asian tiger and yellow fever mosquitoes like people, while many Culex prefer birds, which is how West Nile virus moves from birds into humans and horses. Why some people get bitten far more than others is covered in why mosquitoes bite some people more.

Where mosquitoes live

Anywhere with standing water for at least a week: rain barrels without lids, clogged gutters, birdbaths, plant saucers, old tires, kids' toys, tarps, tree holes, ditches, unmaintained pools and storm drains. Asian tiger mosquitoes rarely fly more than 200 to 300 yards from where they hatched, so if they bite you in the yard, they almost certainly hatched on your block. Salt-marsh and floodwater species, by contrast, can fly miles.

During the day adults rest in shade: tall grass, shrubs, under decks, ivy and dense hedges. Indoors they hide in closets, under furniture and in bathrooms.

When mosquitoes come out and when they go away

Mosquitoes become active once temperatures stay above roughly 50 °F, and they are most active between 80 and 90 °F. In practice:

• Gulf Coast and Southwest deserts: March to November; nearly year-round in South Florida and Hawaii.
• Mid-Atlantic and Midwest: May to early October.
• Northern states and Alaska: late May to September, with intense early-summer peaks.

They "go away" after the first hard frost. Where do mosquitoes go in the winter? Culex and Anopheles females hibernate in sheltered places like crawl spaces, garages, culverts and basements, which is why you sometimes see a sluggish mosquito indoors in January. Aedes overwinter as eggs that hatch with spring rain.

Within a day, house mosquitoes peak at dusk and after dark; Aedes bite in daylight, often around your ankles.

Are mosquitoes dangerous?

For most Americans, a bite is just an itchy bump. But mosquitoes are the main vectors of:

• West Nile virus, the leading mosquito-borne disease in the contiguous US and reported from every contiguous state. Most infected people have no symptoms; the CDC counts about 2,000 diagnosed cases a year (an undercount), more than 1,300 severe illnesses and over 130 deaths.
• Eastern equine encephalitis, rare but severe, mostly in the East and Great Lakes.
• Dengue, with local outbreaks in Florida, Texas, Puerto Rico and Hawaii.
• Heartworm in dogs and cats, diagnosed in all 50 states (American Heartworm Society).

See a doctor if a fever, severe headache, stiff neck, confusion or rash follows mosquito exposure, especially after travel.

What people say about living with mosquitoes

Patterns from Reddit discussions:

• "Why do they even exist?" is the most-asked mosquito question. The best-upvoted answers make two points: evolution doesn't give species a purpose, they persist because they work; and mosquitoes do feed fish, frogs, dragonflies and birds and pollinate some plants. Wiping them all out would hit those food webs, though how hard is debated.
• "I thought they died in winter." Many people are surprised by a slow mosquito in the house in January. Those are hibernating Culex females; Aedes skip winter as eggs. Vets in pet threads add that "winter" is unreliable: a warm November or March means mosquitoes are flying.
• Zappers and porch lights are what people try first and complain about most, for the reason given above: mosquitoes follow CO2 and odor, not light.
• "They're only bad at my house" usually traces back to a container within a few hundred feet: a clogged gutter, tarp, tire, or a neighbor's untended pool.

How to deal with mosquitoes

The short version, detailed on the get rid of mosquitoes page:

1. Dump standing water weekly around the house and treat what you can't dump with Bti dunks.
2. Use an EPA-registered repellent (DEET, picaridin, IR3535 or oil of lemon eucalyptus); see insect repellents.
3. Fix window and door screens, and run air conditioning instead of opening windows at night.
4. Contact your local mosquito control district if a neighborhood-wide problem comes from ditches, marshes or a neglected pool. Many counties treat for free.

Mosquito-repelling plants are pleasant but don't stop bites by themselves.

A note on "mosquito bits for fungus gnats"

"Mosquito Bits" is a product name for corn granules coated with Bti (Bacillus thuringiensis israelensis), a bacterium that kills mosquito larvae. Gardeners also use it against fungus gnat larvae in houseplant soil: sprinkle on the soil or steep in watering water. It is harmless to people, pets and plants, and it does nothing to adult mosquitoes or gnats.