They bite us, we swat them. But there’s more protective action we can take against mosquitoes, armed with some good ecological know-how.
For the past several years, the Missouri Botanical Garden has been working with community organizations and local health departments to help citizens learn more about mosquitoes in our area and practice eco-friendly ways to keep the insects at bay.
Know thine enemy: understanding the mosquito
While we may view them simply as pests, mosquitoes come in all shapes, sizes, diets, and disease-carrying capacities. They also can be beneficial to our ecosystem, plants, and even disease prevention in some unique cases.
Understanding and ID-ing mosquitoes a little better can make help us monitor populations, prevent bites, and find greener solutions.
Growing up in stagnant pools: the mosquito life cycle
All mosquitoes breed in standing water. They’re aquatic through their egg, larval, and pupal stages, becoming terrestrial flying insects as adults.
Eggs
Mosquito eggs are laid in stagnant water. The current in a creek or your yard’s water feature with a circulating pump will not attract a gravid female since moving water will wash eggs away.
After blood feeding, a female mosquito rests for a few days to digest and develop eggs. Depending on her species, she can lay 30-300 eggs at a time. Some species lay eggs singly, some lay them in a cluster called a “raft.”
Mosquitos progress from egg to adult in 7–12 days, accelerating to 3–5 days in very hot weather, 90s and up. This means heat waves, especially after rain, will proliferate mosquitos.
Mosquito Fun Fact: Tiger mosquito females lay eggs on the sides of containers, just above a water line. Eggs can remain dormant for several days to several weeks – and may remain viable for months to years! Eggs rehydrate and hatch when water rises to cover them, helping juicy new larvae survive surface-feeding predators. Buckets, plant saucers, clogged gutters, and your dog’s abandoned frisbee are all excellent breeding sites. One small grace from this habitat preference: Aedes albopictus is unlikely to reproduce in your yard’s soggy soil, so removing or inverting containers is their prime population control.
Larvae and Pupae
Larvae eat decomposing plant matter and microorganisms as they grow through four stages, called instars. When you spot these “wrigglers” around your place, dump or sweep them out.
Pupae look like commas, the punctuation mark. In this “tumbler” stage, they tend to float, jerking into a tumbling dive when water is disturbed.
Larvae and pupae breathe oxygen, rising to their nursery’s surface to respire through a siphon on their abdomen end.
Adults
The adult mosquito develops inside the pupal case. After 1–4 days, depending on species and temperature, an adult splits the pupal case and emerges to the surface of the water, where it rests until its body dries and wings harden.
Males hatch before females and live for only a couple of days. Reproducing is the laser-focus for a mosquito adult.
Do all mosquitoes bite humans?
Did you know that only female mosquitoes bite?
Male mosquitoes lack the proboscis, a tubular mouthpart required to bite and suck blood from an animal host.
A mated female takes a blood “meal” to get the protein she needs to produce eggs. So despite popular belief, this bug’s bites are a reproductive, not nutritional, strategy.
Most mosquitos don’t bite humans. Different species “feed” on birds, livestock, wild mammals and even reptiles and amphibians.
Mosquito Fun Fact: Toxorhynchites, genus of the largest mosquitoes known, aren’t even blood feeders. In their larval stage, these beasts use specially modified mouthparts to eat the larvae of other mosquito species. A single Toxorhynchites can consume as many as 5,300 other wriggling larvae before it pupates. Research deploying them to control populations of disease vector mosquitoes has shown that Toxorhynchites can, in fact, be a Beneficial Insect.
Mosquitoes get their nutrition from sugar in honeydew, rotting fruit, and nectar from flowering plants. Both male and female mosquitoes seek sugar in these substances and use the carbohydrate energy for flight and other bodily functions.
You may have already figured it out, but yes, mosquitoes are pollinators! They’re also vital in food webs because birds, bats, dragonflies, fish, frogs and more eat mosquitoes.
One challenge is finding ways to control mosquitoes without harming the creatures they support.
Do all mosquitoes carry diseases?
Do an online search for “Most Dangerous Animals” and you’ll find this winged wee one out-ranking lions, hippos and crocodiles because of the diseases some – but not all – mosquitoes can transmit.
Mosquitoes can be vectors of viruses like West Nile Virus, St. Louis and Equine Encephalitis, Zika Virus, Chikungunya, Dengue Fever, and Yellow Fever, as well as parasites like Malaria.
Out of more than 3,500 unique mosquito species on Earth, just a few are known disease vectors, and most belong to one of these three genera: Aedes, Culex and Anopheles.
Most mosquitoes species don’t even seek out humans. Most of those that do, like the floodwater or swamp mosquito (Aedes vexans) which proliferates after floods recede, are certainly pests but are not health threats.
ID-ing mosquito species
Educated bite prevention is our everyday best bet.
We distinguish one type of rose or tomato from another, so let’s note mosquito differences too. It’s vital for ecological and human health to understand that not all mosquitoes pose disease threats. With this knowledge, we can deal with them responsibly.
Even a glance can ID features of mosquitoes active in our area. Check out their color, patterns, body posture and leg and wing alignments.
Around St. Louis, you’ll surely see the vividly striped black-and-white tiger mosquito, Aedes albopictus, and the small, brown Culex pipiens, the northern house mosquito.
You’ll also encounter them at different times of the day, another good identifier. With their low tolerance for heat, house mosquitoes feed at dusk and dawn. Tiger mosquitoes tolerate a much broader temperature range, so they will be active day and night.
Mosquito Fun Fact: Sabethes cyaneus, the paddle-legged mosquito, displays a gloriously iridescent shade of blue with elaborate front leg “feathers.” This rare neotropical native is considered the world’s most beautiful mosquito, who does transmit rare tropical diseases.
What attracts mosquitoes to humans?
All mosquitoes share an extraordinary range of sensory capabilities, evolutionary achievements that have them thriving on every continent except Antarctica.
A mosquito’s primary attraction to a blood meal host is the aura of carbon dioxide that every vertebrate exhales. Our personal clouds of CO2 attract ticks and chiggers too.
Tiger mosquitoes can detect the long red-orange light wavelengths emitted by human skin, regardless of skin pigmentation. Most mosquitoes are visually attracted to dark colors. This is why we’re advised to wear “loose, light colored clothing” in mosquito season.
All mosquitoes pick up on fragrance. So summer is a smart time to go fragrance free with personal care and laundry products.
Then there’s body heat, sweat, the chemistry of skin bacteria. For the species that prey on humans, we’re all mosquito magnets, to varying degrees.
Mosquito Fun Fact: Beyond their prey-finding wayfinding, mosquito senses are truly amazing. Their keen hygrosensation – sensitivity to humidity – guides a female to standing water needed to deposit eggs. In a typical yard or park with multiple active species, sex pheromones help a mosquito find a con-specific mate.
How do we protect against mosquitoes while protecting pollinators?
Plants and insects have an ancient, vital, beautiful partnership: pollination. All life on Earth needs bugs, but insect populations worldwide are in serious decline because of habitat loss, light pollution, chemical toxicity, and other factors.
There is some good news though. St. Louis has a dynamic native plant gardening movement that is growing capacity to restore and coexist with insect communities.
Insects like mosquitoes that are human pests and can transmit diseases, are a real community concern. However, dealing with these bugs using routine, blanket chemical sprays harms all insects.
“Mosquito fogging” should be our last resort, strategically deployed to control disease transmission.
Mosquito Alert STL
Staff of the Garden’s EarthWays Center have been working since 2020 on Mosquito Alert STL, a community science partnership with St. Louis County Department of Public Health, the City of St. Louis Health Department, Washington University’s Tyson Research Center and Saint Louis University School of Public Health and Social Justice.
Mosquito Alert STL aids our local public health professionals’ efforts to track mosquito populations and respond to potential disease threats.
Mosquito Fun Fact: The mobile app Mosquito Alert was developed by a team at Universitat Pompeu Fabra in Barcelona, Spain, in response to 2016 outbreaks of Zika Virus. The power of this citizen science support helped prompt the City of Barcelona to establish a Department of Biodiversity. Today, Mosquito Alert is in use across Europe and in parts of Africa and the Caribbean. The Garden and our partners were supported by the Barcelona team to launch the first U.S. edition of this citizen science initiative, Mosquito Alert STL.
This project supports BiodiverseCity St. Louis, a Garden-led community initiative, by educating about mosquitoes while advocating for gardening with native plants.
Chemical common sense
There are two effective, ecologically responsible ways to regularly use chemical mosquito controls:
Protect yourself With mosquito repellant and mosquito dunks in standing water
Technically, mosquito repellants work by blocking some of the sensory cues a mosquito uses to locate you as blood-meal prey. In practice, a repellant is like spraying on an invisibility cloak.
The U.S. Environmental Protection Agency now recognizes eight repellant ingredients as being safe and effective. These include three plant oils in addition to DEET and other synthetic compounds.
Look for these ingredients at the top of label lists of active ingredient:
- Catnip Oil
- Oil of Lemon Eucalyptus
- Citronella Oil
Mosquito Fun Fact: A 2001 University of Iowa study found that nepetalactone, a substance in Catnip Oil, is 10 times more effective than DEET in repelling mosquitoes. Catnip (Nepeta cataria) is a member of the ultra-fragrant Lamiaceae (mint) family of flowering perennials. It’s easy to cultivate with an oil that can be efficiently distilled. Why does it work so well? Reporting this discovery to the American Chemical Society, Dr. Chris Peterson, an entomologist who co-led the research, said, “It’s still a mystery; (the oil) might simply be acting as an irritant or (mosquitoes) don’t like the smell. But nobody really knows why insect repellents work.”
Today you can find plant-based, DEET-free repellants at any big box, pharmacy or garden store chain. You can also find DEET in multiple formula strengths. Local soap and herb shops often make plant-based mosquito sprays.
Because body chemistry varies from person to person, and can change as we go through life, it’s useful to test out a couple of repellants. Find a formula that works for you and use it!
Add fans to your mosquito repellent arsenal
Along with repellent, bringing fans to your outdoor spaces can also keep mosquitoes away.
Mosquitoes are weak flyers, so you won’t find yourself swatting on a windy day. Electric fans in outdoor seating areas will keep your space mosquito-free.
Interrupt mosquito breeding
Eliminating standing water should be your first mosquito repellent measure. But if you can’t get rid of the standing water, you can treat mosquito breeding habitats with Bti (Bacillus thuringiensis israelensis), a bacterium that occurs naturally in soil spores.
This effective larvicide is not a synthetic. It only affects mosquitoes and their fellow members of Diptera, the fly insect order. Widely available and affordably sold as “Mosquito Dunks” or “Mosquito Bits,” they release a toxin in the guts of feeding larvae.
Large scale mosquito control
Our region is fortunate that St. Louis County’s Department of Public Health monitors mosquito populations through trapping, surveillance, and lab analysis. Their professional and seasonal staff also apply larvicide treatments in known mosquito breeding areas on public property.
The department networks with neighboring health departments and informs the community when disease threats occur.
Because these professionals know that fogging can harm pollinators and does nothing to interrupt mosquito breeding, they strictly limit fogging to locations and times when their surveillance shows an uptick in the population of the kinds mosquitoes that can transmit disease.
In summary, here are some helpful tips for keeping mosquitoes at bay in a sustainable, ecological way:
- Wear loose, light-colored clothing when working outdoors. Long pants, long sleeves.
- Use a mosquito repellant! Keep a basket of several kinds for summer play and gatherings.
- Plug in an electric fan when sitting outdoors. Mosquitoes are weak flyers, so a fan breeze will keep them off – and keep you cool!
- Find, dump, and remove containers around your property to eliminate the standing water mosquitoes need to breed. Treat water you can’t remove with Mosquito Dunks.
- Don’t resort to chemical fogging. Bug spray kills bugs, period. Don’t fall prey to advertising claims that will harm pollinators. Educate your local officials about the ineffectiveness and harms of routine fogging.
- Garden with native plants to attract and support a variety of mosquito predators. Biodiversity is nature’s tried and true mosquito population control.
- Join the citizen science project, Mosquito Alert STL, to help local public health agencies monitor and responsibly respond to mosquito activity.
Understanding some mosquito basics can boost our summertime enjoyment, help us prevent disease, and support the many kinds of insects a healthy outdoor environment needs.
Garden staff can advise community groups and municipal officials seeking to optimize ecological mosquito control practices. Our participation in Mosquito Alert STL with public health agency partners has grown our capacity to provide this guidance, in support of pollinators and their plant partners.
The Garden’s Green Resources Info Service is at your service to answer any questions about sustainable living and provide public talks.
Jean Ponzi | Green Resources Specialist EarthWays Center
Thanks to Tad Yankoski, Senior Entomologist of the Sophia M. Sachs Butterfly House for his expertise on mosquitoes.
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