This post contains photographs and construction tips for a killer craft I made: an autocidal gravid ovitrap. Pregnant females enter the trap, lay some eggs on or near the stagnant water within, then are prevented from exiting and die. Their progeny also die because a screen at water level prevents larvae from reaching the surface to obtain oxygen. When similar traps have been deployed they bring down mosquito levels substantially and thus are quickly becoming one of the main ways to prevent mosquito outbreaks and disease. Every homeowner should have six. They’d make wonderful gifts.
The design features a clear dome that helps trap the females when they are done ovipositing (they go for the light), plus a completely unneeded observation window so I can watch the larvae and pupae (fun for the whole family, plus good for demonstration purposes). It borrows general methodology from gravid Aedes traps (GATs) designed by Dr Scott Richie (James Cook University) and colleagues that recently made news on NPR (here’s an overview; here’s their paywalled journal article). I’ve designed mine to capture species that also lay egg rafts, so it’s not just a GAT. My design doesn’t use insecticide because I wanted the odor of developing larvae to be an attractant to other females (it is, by the way).
What you need
6″ plastic pot
clear dome from cake store
metal coat hanger
small neodymium magnet
silicone adhesive glue
1-L soda bottle
1/4″ foam weatherstripping
black spray paint
Dremel tool with cutting bit
drill with drill bit
safety glasses (when Dremeling)
If you’d like to see photographs larger just click on first image and navigate like a slide show. There are many ways to construct these so if you build one and it looks completely different, don’t worry. This is because if your device is the only stagnant water around, females will use it.
Buy an 8″ cake for the clear dome on top. Eat cake.
Cut off bottom of pot, use knife to smooth edge.
Draw circle on dome where funnel will drop in.
Cut hole in dome with Dremel to accommodate funnel.
Glue funnel onto dome. Use Goo Gone to remove labels.
Fit funnel with optional hardware cloth grid.
Cut hole in pail lid with Dremel, then smooth the cut with a knife.
Cut observation window into side of pail.
Cut rectangle out of soda bottle for viewing window.
Glue soda bottle plastic onto inside of observation hole.
Apply bead of silicone sealant to outside of observation window.
Cover observation window prior to painting.
Paint outside of pail and lid black.
Attach clear dome to pail lid with anything but Goop
Bend coat hanger into diameter equal to inside diameter of pail.
Staple fabric screening onto coathanger.
Affix weatherstripping to inside of pail to support the screen.
Make handles for the screen out of paperclips.
Drill drain holes so that water line is barely above screen.
Fill pail with rainwater not tap water.
Add old leaves from gutter, cat food, etc. to bait the water.
Add wood (and/or cloth strips) for egg laying.
Hang sticky card by paperclip held by neodymium magnet.
Situate trap in thick vegetation, protect from rain somehow.
I’ve only just deployed it and it’s rather cold right now so I don’t have any victims yet. But I’m optimistic and am posting now with the hope that somebody will have suggestions on how to improve the design (I’m making more). One improvement I’m definitely going to make is to drop the funnel lower into the dome so it’s harder for females to accidentally fly straight up to escape. And pro-tip if you make the above: attach the lid to pail when spray painting to avoid unwanted buildup where they attach.
I’m also posting in the off chance that a biology teacher might take an interest. Having teams make these would be really fun and then they could deploy them in the woods near the school: bonus points for team that traps the most mosquitoes. It’s fun like the classic egg-drop lab in physics except useful. Students would then take their projects home where they’d continue to be useful. Would make for a great Girl Scout Gold Award / Eagle Scout project.
During a run this week I passed an abandoned, 30-gallon aquarium with easily 10,000 larvae doing their thing (wriggling). I came back later, took some photographs (on my Instagram soon if you’re into that), and then dumped it, sending the larvae to their deaths but also releasing a cloud of perhaps 100 newly-eclosed adults. I suspect the aquarium had been there for years, pumping Asian tiger mosquitoes (Aedes albopictus) into the neighborhood. Given the aquarium’s location at the edge of busy parking lot I’m sure that thousands of people have looked at it and thought, “Huh. Looks like an abandoned aquarium full of dirty water. Next to a Christmas tree. I bet there’s a story there!”, and then moved on with their lives.
In case you are unsure what an infestation looks like, the next two photographs show what the adults, larvae, and eggs look like. Asian tiger mosquitoes lay eggs singly on the sides of containers or on moist objects floating on the water. They can last over a year as an egg, waiting for conditions to be just right.
Here’s a sample of the water I pulled from the tank.
But not all the eggs were Aedes albopictus (there are 60 species in PA alone). Here’s a raft of eggs in the aquarium from a different species (Culex sp.). The raft is lodged on a leaf but normally it just floats around until the larvae pop out. Anopheles (another common genus) has eggs that are deposited singly but float with the help of cute little life preservers.
But that’s not all! Yesterday I found a recycling bin behind a church with similar numbers of larvae. Given the amount of leaves decomposing in the bottom I suspect it has been like this for at least the whole summer. Again, it really is strange that nobody did anything about it. It’s right next to a sidewalk that gets lots of traffic (at least on Sundays) and is probably 10′ away from a playground at an infant/toddler daycare center. Poor kids. (I dumped it.)
Given how much people hate mosquitoes it left me thinking how the public outreach about mosquito control has failed on the most basic level. Everyone should know enough about mosquito biology to know how and where they breed, and everyone should feel empowered to do something. Being proactive is so much better than adopting what I think is the common view, “Well if the mosquitoes get bad enough I’m sure the government will spray insecticides from planes.”
All it would take would be a nicely worded message from a town official to mobilize residents into a mosquito watch. Something like, “If you see mosquito larvae swimming around in a container when you are out walking your dog, please turn the container upside down or alert the owner about it. Thanks.”
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:
Please email me if you think I’ve made an error or if you know that a formulation has changed (which happens). 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 safe but 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 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?
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 the spray can kill 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. E.g., look at this a two-spotted long-horned bee (Melissodes bimaculatus) from my front yard this summer. 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 can 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 (and hilarious) 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.
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 through words or imagery that their pyrethroid-containing sprays are “environmentally friendly,” “bee friendly,” “kid friendly,” “pet friendly,” or government approved (e.g., “EPA-approved”), sue them. Massachusetts did, and now has several restrictions on advertising including a ban on ads that “rely on images of young children to convey a sense of harmlessness“. 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.
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).