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The Basics

If you want to know how to avoid mosquitoes, you need to learn about the different types of mosquitoes found in North America, their life cycle, and perhaps most importantly, the basics about mosquito habitat and behavior. Consider this section of the book your primer to the world of the mosquito.

What Are Mosquitoes?

Mosquitoes are insects. Specifically, they are small flies in the scientific family Culicidae.

For those of you needing (a brief!) refresher on your biology: Scientists use the taxonomic system to classify and catalog life. There are eight categories, or ranks, in it. The general idea is pretty simple: the lower the rank, the more specific you get.

As you can see, just a quick look at the taxonomic system tells us a lot about mosquitoes. We can immediately see that they are insects, and more than that, they are a specific type of insect—true flies—which means that mosquitoes belong to the same order as black flies and the common housefly.

Domain—Eukaryota

Kingdom—Animalia

Phylum—Arthropoda

Class—Insecta

Order—Diptera

(true flies, including mosquitoes)

Family—Culicidae (mosquitoes)

Genus

Species

Mosquito Anatomy

All insects, including mosquitoes, have three main body parts: a head, a thorax and an abdomen. They also have three sets of legs and one or two pairs of wings.

Like other flies, mosquitoes have a number of features² in common: they have one pair of wings, large compound eyes, mouthparts adapted for sucking (or in the case of mosquitoes, piercing), a pair of simple antennae (though mosquito antennae are often long and frilly) and a pair of (often tiny) halteres, small stump-like wing remnants that act as flight stabilizers.

At a quick glance, crane flies look like supersized mosquitoes, but the resemblance is only skin-deep. Not only do crane flies lack the mosquito’s prominent mouthparts, adult crane flies actually don’t feed at all.

Total Number of Mosquito Species Worldwide

There are over 3,500 mosquito species³ worldwide. About half of all species are endemic, which means that they are only found in one country or area. The other half is more widespread, with some species found across thousands of miles.

As mosquito populations are dependent upon heat and the presence of water, mosquitoes are dependent on geography. Generally speaking, the closer one gets to the equator, the more mosquito species you’ll find⁴. (Countries with large areas also tend to have more mosquito species.)

For example, Norway is home to 16 mosquito species. Brazil has over 450.

While we generally think of mosquitoes as drab pests, some mosquitoes are actually gorgeous. Perhaps the most famous example is the species Sabethes cyaneus, which is renowned for its iridescent coloration and its feather-like decorations. If you were bitten by a mosquito like that, at least you’d get a good show!

Number of Species in the Continental United States

The Continental U.S. is home to 166 mosquito species⁵, but the number of species per state and mosquito population density vary widely. Southern states, such as Texas (85) and Florida (80), often have more mosquito species, but not by all that much. Northern states, such as Minnesota and New Jersey, have quite a few as well, 51 and 63, respectively. Even comparatively warm, dry states, such as Arizona and Nevada, have robust populations that can wreak havoc. In short, there is almost no escaping them, so you need to know how to fight back.

Of course, Brazil’s many mosquito species won’t necessarily ruin your vacation in Rio. After all, species numbers don’t say much about population numbers. A case in point: Alaska and Minnesota are home to far fewer species, but they definitely boast more than their fair share of individual critters in “skeeter season.” Unsurprisingly, both Alaska and Minnesota have mosquitoes named after them.

The Mosquitoes to Worry About: The “Flying Syringes”

All mosquitoes belong to one large family of insects—Culicidae. This family consists of two large groups, which are called subfamilies: the Anophelinae (480 species) and the Culicinae (3,000 species). Some species don’t bite humans at all, but a good number are serious pests and a few troublemakers are responsible for spreading serious diseases.

In particular, three groups of mosquitoes are responsible for the vast majority of mosquito-borne diseases. These bad apples are often called the “Flying Syringes.”

Because of their medical importance, it’s helpful to be familiar with them. As it happens, these three groups also include some of the primary pest species—so even if they don’t make you sick, they might still ruin your barbecue.

Culex

Anopheles

Aedes

Anopheles mosquitoes are members of the Anophelinae subfamily. One genus of the Anophelinae mosquitoes—the genus Anopheles—is notorious for spreading malaria. In all, there are 12 species of Anopheles in North America⁷.

Both the Aedes genus and the Culex genus are members of the Culicinae subfamily. There are 11 species of medically important Aedes in North America⁸, and 9 species of medically important Culex.

The Aedes mosquitoes spread yellow fever and Dengue fever.

Culex mosquitoes spread West Nile, a number of types of encephalitis⁹ and several parasitic diseases.

The good news? Cases of malaria, yellow fever and Dengue fever are mercifully rare in the U.S., and those infected have usually traveled abroad. Other diseases—including West Nile—still remain a serious concern, however.

What’s in a Name?

The word Anopheles (a-NOF-o-leez) comes from the Greek word anōophelōes, which translates to “useless.¹⁰”

The word Aedes (AY-deez) also comes from Greek, from the word aōedōes, which translates to “unpleasant.¹¹”

The genus name Culex (CUE-lex) is far less colorful and simply means “gnat” or “fly” in Latin¹².

Even Mosquito Researchers Get Annoyed at Mosquitoes

Some mosquito researchers clearly had some pointed (ha?) opinions about mosquitoes. Want proof? The species names they chose say it all; you’ll probably recognize most of these root words, all of which are used in English: vexans¹⁴ and inundatus and abominator and excrucians and tormentor and horrida. None of them have positive connotations.

Some biologists literally agree with Anopheles’ scientific name and think that mosquitoes are worthless, even calling for the outright eradication of mosquitoes. They argue that the ecosystem would likely be relatively unaffected¹³.

Four Phases of Life

Like butterflies, ants and many other insects, mosquitoes go through four general stages of life: they start life as an egg, which hatches into a larva. After feeding, the larva pupates, where it transforms into an adult.

Where Do Mosquitoes Lay Eggs? Pretty Much Everywhere

Female mosquitoes lay their eggs on or near water, or in areas that will soon be exposed to water. As you might expect, that encompasses much of the U.S., and with over 150 species in the country, there’s a great deal of variation among mosquitoes.

Very generally speaking, there are two types of mosquitoes—floodwater mosquitoes and freshwater/stagnant water mosquitoes. These names are informal, and since mosquitoes are quite opportunistic when depositing eggs, some species undoubtedly fit in both categories. Still, these categories are enough to give the layperson an idea of where mosquitoes lay their eggs—and how one can avoid giving mosquitoes places to deposit eggs.

Floodwater mosquitoes

As their name suggests, floodwater mosquitoes (which includes important Aedes species) lay their eggs in areas that are damp or that will be inundated by water, such as salt marshes or riverside forests. The eggs need to be inundated by water before they hatch, but reduction of dissolved oxygen in the water is the most important factor for egg hatching¹⁵. When levels drop beyond a certain point, the eggs hatch. This ensures that the larvae will be born into the shallow, food-filled areas where the larvae thrive. These mosquitoes often become a scourge after river flooding or the storm surge of a hurricane.

Freshwater and Stagnant Water Mosquitoes

Some species, like the malaria-bearing Anopheles mosquitoes, only lay eggs on freshwater, whereas the notorious pest Culex pipiens lays eggs¹⁶ in stagnant water, everywhere from cesspits and plant pots to hoofprints in cow pastures. The invasive Asian tiger mosquito will deposit eggs nearly anywhere it can—and doesn’t venture far from where it hatches, so if a female of a pest species deposits eggs in the birdbath on your deck rail, you’re certainly on the dinner menu¹⁷. Perhaps surprisingly, flowing streams and deep ponds and lakes are often less ideal environments for most mosquito species, as they have less food, too much turbulence and more predators.

How opportunistic are mosquitoes when finding a place to lay their eggs? During a study in the 1930s, a cage holding research mosquitoes and eggs was inadvertently torn open. When the researchers returned and discovered the damage, they noticed that some mosquitoes had escaped, but wild females had entered the cage and laid additional eggs¹⁸ !

To make matters more complex, some mosquitoes are often referred to as “container” mosquitoes because they are found in a variety of natural or artificial containers. Mosquitoes found in natural containers are often referred to as “woodland” or “treehole” mosquitoes because they are found in wooded areas, and often deposit eggs near trees—or in cavities within them. When it rains, these holes fill in with water, and the eggs then hatch. There are many types of natural cavities—from rotting stumps to containers as specific as a particular type of pitcher plant. In fact, some mosquito species even lay their eggs in pitcher plants, which serve as natural cavities and catch rainwater¹⁹. An African Aedes species even lays its eggs on the legs of crabs, which then transport the eggs to the crab’s nest, where the eggs later hatch²⁰.

Of course, many²¹ mosquitoes are just as comfortable depositing eggs in artificial containers such as gutters, tarps, birdbaths and old tires. Oddly enough, many disease-transmitting mosquito species have been found developing in artificial containers in cemeteries. The vases, toys, and flowerpots left behind by mourners prove to be ideal habitat for these sometimes-deadly insects²².

Eggs: Laid Alone or Together?

In North America, there are two primary ways that mosquitoes lay eggs: some mosquitoes, including all of the Anopheles and Aedes species, deposit their eggs one-by-one, either on the water or on moist soil at the water’s edge, whereas nearly all²³ Culex species (and those of a few other groups) glue their eggs together to form an egg raft, which floats on the water and rebounds to the surface when submerged.

When female mosquitoes build an egg raft, they are nearly totally committed. According to the observations of one researcher, Culex females were so focused on building an egg raft that one could be picked up from the surface and didn’t try to fly away²⁴. Talk about a maternal instinct!

Waiting It Out: Dormancy

If the conditions aren’t right, the eggs of some species can become dormant; dormancy can last for some time—the eggs of some Aedes species²⁵ can remain viable for up to four years. When floodwater eggs are laid in cooler weather, the eggs remain dormant until the weather warms. This is also why Dengue fever and other diseases carried by Aedes mosquitoes often spike in spring or during the monsoon season in tropical areas.

Whereas most mosquito females simply deposit their eggs and leave, one species in South America actually broods its eggs, protecting them until they hatch²⁶. While this is common in other insects, it’s the only mosquito species known to do so.

The Eggs Hatch and Larvae Emerge

Mosquito eggs usually hatch within a few days, but under ideal²⁷ conditions, some species can hatch within just 30 hours. Larvae are colloquially referred to as “wigglers” thanks to their wiggly swimming motions. Larvae have two primary jobs: eating and molting. Larvae go through four molting periods, each of which is referred to as an “instar.” After hatching, the larva is in its first instar. Once it molts, it is in the second instar, and so on.

With each molting period, they get larger. Of course, to grow, they need food, and eating is their specialty. Larvae are almost always filter feeders and eat a variety of algae, single-cell organisms and plant material. In some Culex species, larvae are fierce predators, consuming many larvae of other mosquito species, and even members of their own species²⁸.

The length of the mosquito’s larval stage depends on the species and the conditions but is usually a matter of 7–10 days²⁹.

Let’s Go Snorkeling!

All mosquito larvae are aquatic, but they still need to breathe air. So how do they do it? Aedes and Culex mosquitoes essentially use a snorkel, which is technically called a siphon. When resting, they hang down from the snorkel. Anopheles species lack this snorkel and instead lie parallel against the water’s surface, breathing through tubes on their abdomen³⁰.

Some larvae have even more ingenious methods of breathing. Mosquitoes in the Mansonia genus are wholly aquatic. They drill into underwater plants³¹ in order to obtain oxygen.

Pupation: Real-Life Transformers

Like moths and butterflies, mosquitoes pupate, but mosquitoes pupate in water. There they develop into adults and then somehow manage to emerge from the water’s surface and fly away. The transformation is like something out of science fiction; when they go in, they are worm-like aquatic creatures that get around primarily by wriggling and that eat phytoplankton and one-celled organisms. When they emerge as adults, they are six-legged flies that subsist on an entirely different diet—sugars from plants.

Pupation periods vary significantly by species and the local conditions—generally, warmer conditions speed things up, but adults usually emerge in a matter of days.

The pupae of one type of mosquito species are reported to glow in the dark. Found in Brazil, these species glow slightly in a purplish hue³².

Surprise, Adult Mosquitoes Are Vegetarians!

Once the adult mosquitoes emerge, they have two main jobs: eating and mating. Mating usually happens first and takes place at or near the site of emergence. After mating, the females forage for a blood meal; they do so because the proteins found in animal blood—specifically chains of amino acids—help them³³ to produce more eggs. Without a blood meal, most species can’t produce eggs. There are a few exceptions; such species are called autogenous and can produce eggs without a blood meal³⁴.

When most female mosquitoes seek out a blood meal, humans often aren’t their preferred species. When given the choice, mosquitoes often prefer livestock, such as sheep³⁶. So why do they pester you at your barbecue? Because we are often the most numerous host in their habitat.

So what do mosquitoes actually eat? Sugars, usually from nectar or fruits. In the lab, scientists often feed adult mosquitoes a simple mixture of sugar water³⁵, though research mosquitoes have also dined on corn syrup, fruit juices and raisins, among other things.

Mosquito Mating: Music (and Dancing) in the Swarm

Mosquitoes usually mate in swarms—large collections of males that are frequented by females³⁷. As it turns out, it’s a surprisingly musical affair. The female mosquito’s characteristic buzzing sound is actually music to the male’s ears, and they are attracted to the sound. (In fact, in 1948, researchers armed only with a tuning fork tuned to the female mosquito’s frequency were able to attract male mosquitoes.)

The males in the swarm are pretty musical as well—as they “dance”³⁸ amid the swarm, and when the male and female approach one another, they harmonize, creating the equivalent of a mosquito love song³⁹!

The Anopheles mosquitoes don’t mate right away because they have to undergo some . . . changes⁴⁰. In what must be a terrifying process, during the first 12–24 hours of the male’s adulthood, his genital organs are inverted—turning a full 180 degrees. This orients them correctly so mating can occur.

Hibernation/Overwintering

So how do mosquitoes survive the winter? It depends. Some species overwinter as adults, usually in a well-sheltered area, such as a cave or a culvert. Other species survive in the egg stage or as larvae. Either way, the mosquitoes are raring to go when the weather warms up.

St. Paul, Minnesota, has many well-known caves. A mosquito researcher happened upon one of these caves, which was being used to grow mushrooms, and discovered millions of hibernating⁴¹adult mosquitoes.