Tag Archives: vector

Eliminate mosquitoes by eliminating stagnant water


1. Gutters


2. Flexible downspout extenders


3. Tarps


4. Toys


5. Bird baths


Bird bath next to purple coneflowers

6. Trash and recycling bins


Recycling bins with stagnant water

7. Watering cans


8. Wheelbarrows


9. Rain barrels


10. Pot saucers


Other places where mosquitoes larvae thrive

Other objects of concern are: pool covers, pot saucers, grill covers, plastic kid toys, tires, unattached hoses, empty glazed pots, shovels, construction materials, garbage cans, garbage can lids, containers in recycling bins, bottle caps, cemetery vases, decorative shells, empty coconuts, papaya tree stumps, downspout troughs, spigot drips, ollas, pickup truck beds, window wells, septic tanks, uncapped metal fence posts, animal tracks. Mosquitoes will also lay eggs inside in toilet bowls, animal water dishes, and French drains.

Effects of mosquito sprays on humans, pets, and wildlife

Mosquito Authority, Mosquito Joe, Mosquito Platoon, Mosquito Shield, Mosquito Squad, TruGreen, and many other companies often imply that the insecticides they spray on yards are safe for everything except mosquitoes. These companies are also very reluctant to reveal what chemicals they use. This page contains information on what, exactly, they spray and what effects those chemicals have.


Please email me if you think I’ve made an error or if you know that a formulation has changed (which happens). All of the chemicals are either pyrethrins or pyrethroids, which are natural and synthetic (respectively) neurotoxins that cause almost instant paralysis and death to mosquitoes. Below is the chemical structure for one, permethrin:

Are these chemicals safe for humans?

Pyrethroids are relatively safe but should not be viewed as harmless. If you spill enough on your skin you might experience itchiness, numbness, nausea, and respiratory problems, among a rather long list of adverse events. Although you obviously can’t test whether pyrethroids harm human brains, studies on mice and rats suggest that the chemicals do act on mammalian nervous systems; that should at least give you pause if you have kids rolling around on the grass after the yard gets dosed. Indeed, there is at least one correlational study that suggests exposure to pyrethroids is not good for kids (or at least boys). There are also scattered reports that some pyrethroids are carcinogenic and estrogenic but I don’t think such effects are shockingly large, and to date they seem to be restricted to mouse studies. At very high doses pyrethroids can kill you, a fact known because some people have injected it (suicide) and in one case because somebody ate food that was cooked in pyrethroid concentrate (it resembles cooking oil).

Are pyrethroids safe for pets?

Dogs and chickens seem to be fine. Cats, however, lack sufficient levels of a liver enzyme that helps detoxify pyrethroids and can thus develop what is called pyrethroid toxicosis. A good indicator of cat sensitivity to pyrethroids is the standard warning of keeping cats away from pyrethroid-treated dogs. I.e., if you dose your dog with a large amount of pyrethroids (to kill fleas, e.g.), cats that cuddle with the dog are at risk. If you’d like to see a video of rag doll cat with pyrethroid poisoning (you probably don’t), here’s a video.

Do pyrethroids kill other animals? 







Pyrethroids can kill ALL arthropods, in fact, not just insects. So if a yard is sprayed, likely you’d likely find dead spiders, mites, centipedes, and millipedes.

One obvious consequence of gassing all the arthropods in a yard is that bird species that eat arthropods will have a lot less to eat. Population levels of swallows and flycatchers, for example, have dropped in last several decades and one explanation is that there are fewer insects to eat.



Note that people who spray their yards with pyrethroids will still have butterflies, fireflies, etc. They just won’t have as many, and likely the some of the ones they do see are from the neighbors’ yards. And people who have their yards sprayed with pesticides invariably won’t perceive the drop in wildlife numbers and will likely truly believe that the sprays are harmless to everything but mosquitoes. Confirmation bias is a fundamental part of human nature. And, of course, everyone believes they are immune to confirmation bias.

Do pyrethroids affect plants?

As you might expect, plants that depend on pollinators are likely to have reduced seed production if dosed with an insecticide. E.g., Brittany Harris found reduced reproductive success of rare plants in Florida when they were located near houses sprayed with insecticide. Pyrethroids can also harm plants directly (e.g., Tu 1981, Bragança et al. 2018).

Pyrethoids are engineered to last for weeks

As mentioned above, pyrethroids adhere to plant surfaces and stay chemically active for weeks, so the risk to all the organisms mentioned above can last for weeks. Here’s a a description of pyrethroid persistence that I found on a Mosquito Squad FAQ:



Signage and notification requirements




How local governments can help

All towns and cities should maintain a web page that provides mosquito information and relevant pesticide laws to residents. Towns can also enact ordinances on third-party pesticide applications. For example, a town might require that franchises alert neighbors 48 hours before spraying is done.


Is spraying effective?


But I don’t want to imply that spraying is completely ineffective. Pyrethroid fogs will probably kill a large percentage of Anopheles spp. (vectors of malaria) and Aedes spp. (vectors of dengue, yellow fever, Zika, etc.) because these species are more likely to be lower in the vegetation.

Do garlic sprays work?

Many pest-control companies offer a garlic-based spray, too. I haven’t been able to find any scientific publication on these sprays. They might work. But they might also just cater to people’s hopes. Ask the company for printed efficacy data and pass if all they give are testimonials and promises. If you know of a peer-reviewed article showing that garlic spray kills and/or repels mosquitoes, please contact me and I’ll include here.

Automatic fogging systems

For about $4,000, some companies will install systems that dispense pyrethroids over your yard at regular intervals. Don’t do this. Just don’t.

Alternatives to spraying

Here are my tips.