An interview with experts: Are backyard mosquito sprays safe and effective?

Person spraying pesticides in air
July 20, 2020

We get a lot of questions and concerns about backyard mosquito sprays. We interviewed two experts to learn more about the risks.

Each year, more yards are being sprayed for mosquitos. Did you know you could be poisoning your yard but mosquito populations are not being reduced?

Before deciding to spray your yard, know the facts. Spraying can harm you, your kids, pets and your neighbors. The chemicals can also harm birds and insects that help eat mosquitos and pollinate your yard.

To learn more about the problems with mosquito spraying, we interviewed Deborah Landau, an entomologist and conservation scientist at The Nature Conservancy, and Mary Travaglini, a certified organic land care professional and organic landscape manager at the Montgomery County, MD Department of Environmental Protection. These experts agree: Mosquito treatments, including the alleged “all natural” variety can harm you and your environment, while not actually reducing mosquito populations.

Person spraying pesticides in air

How effective are mosquito sprays?

MT: Published and peer-reviewed research by Professor David Pimentel shows that only 0.1% of the pesticides on average reached the target pests. [Pimentel, Cornell University 1995]. When Pimentel looked specifically at flying insects in the study, like mosquitos, the average was less than 0.0001%, or only one in a million. This is because the droplet size of a pesticide must be small and must float in the air.  The droplet size of a mosquito spray must be so small that the chemicals must float in the air, but they also easily drift out of the target area, killing other insects or mingling into the air we breathe.

DL: Sprays can only kill mosquitos that are in your yard at the time of spraying. Mosquitos typically fly 1-3 miles, so they can quickly re-populate your yard. A commercial mosquito treatment will be more likely to kill butterflies, bees and ladybugs in your yard at the time of application than the mosquitoes you’re trying to get rid of. Mosquitos are most active at dawn and dusk, but mosquito spray companies often come during the day when most pollinators are active.  If the treatments target standing water, beneficial insects that eat mosquitos, like dragonfly larvae, will also be killed. If the spray is focused on wet areas, such as piles of wet leaves, chances are they’re killing far more fireflies than mosquitos. Sadly, birds will often pick up insects killed by insecticides, and eat them or feed them to their young.

Dead bee in a flower

What am I getting for my 300 dollars’ worth of a pesticide spray?

MT: If we turn the .0001% effectiveness into dollars and cents, a millionth of $300 dollars’ worth of spraying is .0003, which is not even a third of a penny. In fact, we’d have to spend $10,000 before we even got once cent worth of value! Spend your time and money cleaning gutters, removing standing water, and getting together with the neighbors to do this throughout the neighborhood.

DL: Over time, mosquitos become resistant to pyrethroids (the active ingredients most mosquito treatments) through gene mutation in mosquito populations. Mutations in just this one single gene are enough to make mosquitos in one area resistant to the pesticides very quickly. Companies that spray on a regular schedule will make your mosquito population become resistant even faster. So essentially, you’ll be left with a yard and neighborhood full of super skeeters.

Mosquito staying dry under a wet leaf

Is there anything I can do to control mosquitos in my yard besides spraying?

DL: If you want more bang for your buck, purchase BTI mosquito dunks; they’re cheap, effective, and easy to use (you just place them in areas that hold water). And these are a bacteria that will only kill mosquito larvae. You should always remove standing water from your yard, including under flowerpots, inside wheelbarrows, and pretty much on anything plastic. Don’t forget to clean out your gutters even in summer (you’ll be rewarded with a dry basement in addition to fewer mosquitos)!

MT: There’s a reason why Disneyland, in a part of Florida with lots of mosquitos doesn’t use pesticides to control mosquitos. They take an approach that neighborhoods, HOAs, and businesses can all use right here—they ensure water doesn’t stay standing long enough for a mosquito to lay its egg and hatch into an adult—which is about 7 days.

Cleaning gutters reduces mosquitos

I still hear about West Nile virus? Is this a concern?

MT: The CDC reported 6 cases of West Nile in Maryland in 2019, and no deaths. In 2018, there were 245 cases of all types of mosquito borne illnesses in Maryland, although it cannot be attributed to whether those were carried in the bodies of visitors or spread by mosquitos in the State. I looked up estimated cancer diagnoses for the first half of 2020, and we’re already at nearly 35,000 cancer cases. I’ll choose long sleeves and clearing standing water instead of spraying chemicals that won’t actually be effective but are a risk to my health.

DL: Prevent mosquito bites by wearing long sleeves and using non-toxic repellents that use oil of lemon eucalyptus (OLE). Data shows OLE-based repellants are just as effective as the synthetic DEET formulations. DEET can be toxic at high levels and can damage synthetic clothing. A fan on your deck can be surprisingly effective – mosquitos are weak fliers, and the breeze from a fan will not only cool you off but will keep them away from the area.

What about the “all natural” alternatives that a company has told me about?

MT: Companies might describe that the chemicals used are derived from chrysanthemum flowers, but they are not from plant extracts. Commercial pyrethroids are synthetically produced to mimic the same properties of the pyrethrins in chrysanthemum flowers. Both chemicals paralyze the nervous system of many insects, but synthetic pyrethroids and the undisclosed chemicals they are mixed with are designed to be more lethal. Pyrethroids are neuropoisons in humans, and can cause rashes, respiratory distress, allergic reactions, headache, nausea, convulsions, and more. The additives can cause a host of other reactions. Pyrethroids are also very toxic to fish and other aquatic life, and spread easily on the wind to neighboring properties and into streams. The chemicals can persist on surfaces for days, further killing insects that come into contact.

MT: I looked up the data from the national poison control centers – over 27,000 calls were placed to poison control in 2018 for pyrethrins and pyrethroids, accounting for over 33% of the pesticide calls to poison control alone! Imagine how many more exposures are unknown.

Child sitting in the grass

Here’s another tip: If you’re looking for a way to reduce the entire population, consider these simple devices called OviTraps—used by the military around the world effectively to reduce mosquito populations. Don’t forget to keep removing standing water from your yard all summer long and remind your neighbors to do the same. Your neighbors, pets, birds, pollinators, fireflies and skin will thank you!


9 comments on "An interview with experts: Are backyard mosquito sprays safe and effective?"

  1. Scott Gordon says:

    In Montgomery County a major pest mosquito is the Asian tiger mosquito, an aggressive day biting invasive species. This species often remains in the immediate environment, flying only a few hundred yards, especially when the location provides all of its essential living requirements: a bloodmeal source for reproduction, sugar/nectar for energy, adequate resting sites and available egg laying sites. I agree that there are alternatives to backyard pesticide spraying such as using environmentally friendly alternatives like Bti, but I would not recommend ovitraps for general use. While they are frequently used by scientists as a mosquito surveillance and research tool, they can become a problem if not properly maintained. Ovitraps are small soup-size cans, painted black, partially filled with water and provided with a substrate (wooden paddle or paper lining) on which mosquitoes will lay their eggs. Ovitraps must be inspected and maintained on a weekly basis which includes replacing the egg substrate, dumping out the water and replacing it with new water). Failure to do this maintenance can result the ovitrap becoming a mosquito producer. Any eggs laid on the substrate will hatch when it rains and the new breeding site will attract more tiger mosquitoes. Since ovitraps are often put out in large numbers, a portion often go missing, either through the action of animals or just failure to relocate a trap. Another drawback to ovitraps is that they do not trap and kill the egg laying female mosquito. Since container breeding mosquitoes often practice “skip oviposition” where they lay only a portion of their eggs in any one container, by not trapping the egg laying female the ovitrap at best collects only a small portion of her eggs and she can move on to other sites. A better alternative is the gravid Aedes trap (GAT) which traps the egg laying female on a sheet of sticky paper inside the trap before she can lay her eggs thereby preventing both the next generation of eggs from hatching and removing egg laying females from the population. These traps require no power, use no toxic chemicals, are relatively inexpensive and require very little maintenance. Several neighborhoods in Montgomery County are encouraging residents to join in large scale tiger mosquito control programs using GAT traps. A paper published in Nature in 2018 by Brian Johnson and others “Neighbors help neighbors control urban mosquitoes” describes the results of first 2 years of a control program using GATs in University Park, MD. The paper is open access and available at

  2. Richard Kramer says:

    Keep in mind that the Ovitraps are effective for some aedes species as Scott mentions. The problem is with other genera such as culex that have a greater flight range.

    Disney isn’t a good model for residential mosquito management. They control 10s of thousands of acres so they can larvacide and use other methods to prevent larval development – manage the breeding sites ( water) and you control mosquitoes. You can not control your neighbors yards and their breeding sites.

  3. JIM ORISCAK oriscak says:

    ENJOYED READING THIS.. I was not aware of the harm to other insects / birds / humans.. The sellers of the spray product tell you that it is 95 -98 % effective and that there are no harmful effects to humans.. If this is an obvious lie how can they get permits to do it.???

  4. In one breath you say mosquito treatment only kills what’s in the yard at time if treatment, ignoring fact that insecticide used is residual type, minutes later in sane interview you say chemicals persist on surfaces for days which recognized residual properties but also means it kills future mosquitoes.visitirs not present in yard at time of treatment so…which one is it? This interview is do misleading , almost every sentence is a falsehood. No, mosquitoes don’t develop pesticide resistance in one generation, nature doesn’t work that way, no, droplets don’t need to “float in sir” and no, treatment in sunny time is ad effective if not more as mosquitoes will be wherever the sun is not. Spraying at dawn or dusk us idiotic, you spray not shoot, you don’t need to hit the target, you cost the harborage area and that could be done at 1100 hrs just fine. The don’t hurt the dragonfly by treating standing water advise followed by few n the standing water is pure Saturday night material hehe, As for Disneyland…tjrh have an army if underpaid workers spraying a garlic-infysed solution. Customers will never afford such a bill, besides, using garlic will kill the cats, mice will be delighted hahahahh, not an option for the regular customer. Miss Landau, I am a nice guy, if you need to learn about mosquitoes let me know, no charge. Just stop spooking the public with nicely sounding nonsense

    1. Scott F says:

      So you’re saying these mosquito treatments don’t kill good insects like honey bees, ladybugs, butterflies… etc?

      1. george lemieus says:

        There is no 100% “it doesn’t kill beneficial insects” treatment out there but by not touching blooming flowers risks to honey bees is minimized. Ladybugs…once in someone’s attic then living spaces they are not seeing “beneficial” at all, rather invasive so see, beauty is in the eyes of the beholder. Nothing is bad or beneficial all the time and nothing is safe, problem is with virtue signaling idiots that like to complicate everything with useless ideas/concepts despite having no experience in basically anything except “caring” because caring is easy, requires no money nor effort. Wanna hear something funny? The most “concerned” citizen bending backwards to prove how evil pest control companies are usually live in condos with 1 or zero plants there so I am always on guard when I am questioned by “concerned” citizen especially when they come with loaded questions like yours, like “are you saying alcohol is always good? You know exactly what am I saying, stop wasting my time with gotcha questions.

        1. Lori says:

          So George you are saying it can kill honey bees by saying NOT 100%. We will take that as a yes. The other point you bring up is NOT to let the pesticides touch blooming flowers? Now how exactly are you going to stop a spray/mist from landing on flowers? Huh? Who’s making more sense here? I have made my mind up.
          You’re bullying attitude does nothing but make you look even more suspicious than the ridiculous examples you made.

  5. manish says:


  6. Angelica freund says:

    Well of course… they tell you what they need to tell you to get business. Many people have bought into these franchises, up to $20,000 , and what happens to that investment if people realize that the spray is toxic. Just look up on MSDS site or Material safety data sheet. Look up the chemicals Pyrethins and pyrethroids. This is actual scientific data and it’s actually horrifying that the EPA allows this to be sprayed in neighborhoods by inexperienced kids on school break. There will always be someone who twists the truth.
    But these stats dont lie. These are neuro poisons and I have personally experienced the headaches the respiratory distress and more. Causing me to have to leave my home for hours. It’s even more crazy that you can be outside enjoying a BBQ and next thing you know some kid shows up with a loud backpack blower and huge clouds of chemicals are filling the environment. And this is legal. Not even a warning. And epa does not look out for the little guys best interest. Dont believe that for one minute. I do like the article and the good tips about neighbors working together to control with the traps. Maybe not perfect but it sure beats poisoning the environment and those who make their home here.

Leave a Reply

Your email address will not be published. Required fields are marked *