Mosquito Authority, Mosquito Joe, Mosquito Platoon, Mosquito Shield, Mosquito Squad, and many other companies often imply that the insecticides they spray on yards are safe for everything except mosquitoes. This page contains information on what, exactly, they spray and what effects those chemicals have.
After a little digging, I think I’ve uncovered most of the active ingredients used by these companies:
- Mosquito Authority: bifenthrin, deltramethrin, permethrin
- Mosquito Joe: lambda‑cyhalothrin
- Mosquito Platoon: permethrin
- Mosquito Shield: D-allethrin, bifenthrin
- Mosquito Squad: bifenthrin, cyfluthrin
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 pyrethroids, synthetic neurotoxins that cause almost instant paralysis and death to mosquitoes. Below is the chemical structure for one, permethrin, a common ingredient of lice shampoo:
I still haven’t figured out whether companies permit their franchise owners to pick and choose which insecticides to use, so when multiple chemicals are listed above that doesn’t necessarily mean the sprays will contain both.
Are these chemicals safe for humans?
Pyrethroids are relatively non-toxic for humans but they should not be viewed as harmless. If you spill enough on your skin you might experience itchiness, numbness, nausea, and respiratory problems, among a long list of adverse events. At very high doses pyrethroids can kill you, a fact known because some people have injected it and in one case because somebody ate food that was cooked in pyrethroid concentrate (it resembles cooking oil). 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. Each pyrethroid listed above has a slightly different toxicity, so to get more information Google the name or read the linked material by clicking on their name.
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 they can develop what is called pyrethroid toxicosis. A good indicator of cat sensitivity to pyrethroids is the standard warning of keeping them away from pyrethroid-treated dogs. I.e., if you dose your dog with a large amount of pyrethroids (to kill fleas, e.g.), friendly 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?
Yes. For example, the spray kills monarch caterpillars, even weeks later later due to the presence of insecticide dried onto milkweed leaves (Oberhuaser et al. 2006). And kills honey bees, even if honey bees are inside their hives when the pyrethroids are spayed (workers bring small amounts back to the hive the following day if they land on treated plants or if they find small puddles of water to drink). Sublethal amounts of pyrethroids can change honey bee behavior and make workers smaller. I would imagine the pyrethroids would end up in the honey, too. And pyrethroids kill fireflies, which are most active in a yard in the late evening when mosquito-spraying franchises like to fog.
My favorite group of unnoticed insects that are killed by evening pyrethroid applications are solitary bees, of which there are approximately 4,000 species in the United States. These are bees that collect pollen and nectar during the day but spend their evenings and nights in holes (e.g., mason bees) or clamped to low vegetation. At right is one from my front yard this summer (it’s a two-spotted long-horned bee, Melissodes bimaculatus). Everyone has dozens of species of native bees in their yards but few people realize it. But they are amazing pollinators and almost all adorable. So when pesticide applicators claim their pyrethroid sprays “don’t harm bees” or are “bee friendly”, that is entirely untrue. It’s simply a marketing slogan they were taught when they bought the franchise, and they will insist it’s true even when presented with evidence to the contrary.
Anyone using a spraying service is, therefore, killing all of the above and more. Insects are small and easy to ignore, but if you were to go out after a spraying and look very carefully, you’d find thousands of dead insects on the ground. And only an extremely small percentage would be mosquitoes. If you go out immediately after a spraying you can even see the twitching that precedes death (movie). It’s probably not a pleasant way to go.
Pyrethroids kill all arthropods, in fact, not just insects. So if a yard is sprayed, likely 100% of spiders, mites, centipedes, and millipedes would be at risk. In total that could mean tens of thousands of individuals left twitching in treated yards. In one estimate, an acre of land in Pennsylvania contains 425 million animals … and a good portion of them would be killed by pyrethroids.
Another concern with gassing all the arthropods in a yard is that those 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.
And then there are fish, which are acutely sensitive to pyrethroids. Franchise owners will generally avoid spraying near people’s fish ponds and bodies of water. Indeed, by law pyrethroids can’t be used near water, though there are many reports of franchises ignoring that regulation. Even if a property doesn’t have a pond or stream, pyrethroids are rather stable in the soil and tend to get washed into nearby streams after rains. It is increasingly accepted that runoff of pyrethroids into creeks can kill fish downstream.
Finally, pyrethroids are toxic to certain earthworms. This is probably especially true for those species that come out onto lawn surfaces in the evening, when pyrethroids are often applied. To be honest, many people don’t really care about earthworms (some hate them) but for people who love aerated lawns it should be pointed out that fogging with pyrethroids might result in dramatically less aeration and dramatically more odor from rotting earthworm carcasses. And, perhaps, result in robins that wonder where all the worms have gone.
Pyrethoids are engineered to last for weeks
As mentioned above in reference to monarchs, pyrethroids adhere to plant surfaces and stay active for weeks, so the risk to all the organisms mentioned above also lasts for weeks. Here’s a nice description of pyrethroid persistence that I found on a Mosquito Squad FAQ:
“How can the barrier spray continue to kill mosquitoes for 21 days?
Mosquitoes will feed on plant juices. When they attempt to feed on sprayed leaves, the residual from the spray will kill them.“
Mosquitoes don’t eat leaves, of course, but the quote is correct about the fate of insects that walk on treated leaves. Pesticide franchises like to claim that once their product is dry it is no longer toxic, but that claim makes no logical sense in light of their claim that the product provides protection for three weeks. Some pyrethroids can even last for 90 days if they are on shaded surfaces. One possible reason (in my view) that pyrethroids retain their ability to kill is that morning dew and guttation (see photographs) might re-suspend the pyrethroids on plant surfaces, and then insects walk through or drink these droplets (see photographs).
Signage and notification requirements
All of the above information is of course useful to those interested in getting their yard fogged, but it’s also important for neighbors of treated properties. The reason for this is because the aerosolized pesticide always drifts onto neighboring properties a bit (sometimes a lot). So if a neighbor has a patch of milkweed or a vegetable garden right along the property line, pyrethroids will kill monarchs and coat the vegetables. Homeowners should always check with neighbors before hiring a spraying service and should always personally inform neighbors when the spraying will actually take place.
There doesn’t seem to be a Federal law requiring either signage or neighbor notification when a yard is sprayed with insecticide, and state laws are variable (here’s a good review; here’s another). Many states have laws that require applicators to leave signs at properties that have been sprayed, and some require notification of neighbors prior to spraying. For example, most counties in New York require that neighbors be notified 48 hours before spraying (details). In some states (e.g., Maine) you can get your name on a notification registry that requires any applicator to contact you in advance of spraying. That’s also an option for beekeepers in some states, too; in that case the pesticide applicators need to search a database of hives in a town, then notify hive owners when spraying will happen.
I live in Pennsylvania, one of several states that allows people to be placed on a Pesticide Hypersensitivity Registry. Once on it, pesticide applicators will know you have a medical issue with pesticides and they are obliged to inform you of future spraying (so you can leave the area). Also on this registry are beekeepers, apparently.
If you want to know what rules might apply in your state, Googling “pesticide notification laws regulations residential pennsylvania” (replace with your state) will get you started. If that doesn’t help just contact your state agency that regulates pesticide use. Towns and cities will sometimes have their own rules but some states prohibit such rules.
Is spraying effective?
Although spraying pyrethroids might be a good way to kill mosquitoes near the ground and in low shrubs, some mosquito species spend most of their time high up in the canopies of trees and are untouched by sprays. For example, many species in the genus Culex (transmitters of West Nile virus, St. Louis encephalitis, eastern equine encephalitis, western encephalitis, avian malaria, etc.) are tree dwellers and only occasionally come down to feed on humans and pets. This limitation isn’t just theoretical: one study showed spraying didn’t reduce numbers of Culex at all. So if you have trees and birds, don’t expect that spraying will be effective. Continued spraying will also result in mosquitoes developing resistance to pyrethroids, something that is happening in Africa already.
But I don’t want to imply that spraying is 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. There are more genera of mosquitoes, of course, so depending on where you live and what is growing in your yard, pyrethroids might vary in effectiveness. I think most companies suggest that their sprays might miss 10% of the mosquitoes on a property (that leaves quite a few mosquitoes).
Prevention is cheaper
Preventing mosquitoes from breeding in the first place is entirely achievable if you do two things regularly during the spring and summer:
- Eliminate all places where water pools (unused kid toys, wheelbarrows, clogged gutters, open buckets of water, etc.). Mosquitoes can breed in very small volumes (bottle caps, e.g.).
- Regularly add Bti granules to ponds, water features, and bird baths that can’t be eliminated or drained. Bti (Bacillus thuringiensis israelensis) is a bacterium that kills only mosquito larvae and can be purchased at local hardware stores or online (e.g, Amazon sells Mosquito Bits and Mosquito Dunks).
The Bti isn’t free, of course, but it’s a lot cheaper than the $800 you’d spend on a spraying subscription. If you want to be the block hero, spend your savings on Bti granules for all your neighbors. Just leave the Bti on porches in a gift bag along with a nice card that explains the game plan.
How local governments can help
All towns and cities should maintain a web page that provides mosquito information and relevant pesticide laws to residents (I designed a template if your town needs one). In addition to maintaining the page, local governments should push prevention by sending to residents timely, regular reminders — with visuals — about how to prevent mosquitoes from breeding. Such tips might be especially important for towns that strive to be pollinator-friendly (e.g., Bee City USA, Pollinator Friendly Alliance, Mayors’ Monarch Pledge). 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. Or, at the very least, towns can remind residents that neighbors can (usually) ask franchises to provide alerts before the next spraying so that cats are inside. Finally, local governments should consider banning automatic pesticide foggers (pipes that deliver pyrethroids on a timer, just like those automatic misters in the grocery aisle).
State governments can can also make sure that pesticide franchises are not making false claims. E.g., if companies claim that their pyrethroid-containing sprays are “EPA approved,” “environmentally friendly,” “bee friendly,” “kid friendly,” or “pet friendly,” sue them. Almost all sites I’ve looked at have misleading wording, especially the claim that pyrethroid-containing sprays “target” mosquitoes and ticks (completely false; they do no such thing). Some sites also use misleading graphics and logos (like the one on the right, from a Mosquito Squad site in Florida) to suggest that the EPA has approved the products on a page. I could be wrong, but I’m fairly sure that the EPA neither approves any of these chemicals nor provides that logo. But a typical homeowner might be fooled into thinking otherwise — that’s why state oversight is needed.
I highly recommend “Ecologically sound mosquito management in wetlands” produced by The Xerxes Society. If you’re looking for a comprehensive guide to ridding your yard of mosquitoes, please see my “Mosquito control tips” page. If you prefer your mosquito news and killing tips via Facebook, try Mosquito Control Tips.
Please share this post with your friends (especially beekeepers and monarch fans) and with groups that might care about biodiversity. And with neighborhood groups if you have those — most folks simply don’t know what these sprays actually do, and the franchises are not reliable sources of information.
If you notice death of any type of animal after a spraying event, report the incident to the EPA. Once you’ve done that send me photographs.
If you have questions. please send me an email.