Killing Mosquitoes: The Good, The Bad and The Weird

You’ve heard that saying – Be careful what you wish for! I’ve been waiting for those classic hot-‘n’-muggy summer days to finally arrive here in Southwestern Ontario. In my mind, it ain’t summer until you and your can of cold beer are both sweating buckets. But with humid weather comes mosquitoes. And so the battle begins. As it turns out, how we wage war with these critters can be hugely impactful in terms of effectiveness and in terms of being environmentally responsible.


CITRONELLA CANDLES: According to a recent article posted by The New York Times, citronella candles actually don’t work. Published recently (May 26, 2022), an article unequivocally entitled “Citronella Candles Don’t Really Work. Stop Buying Them” goes into great depth about why one of our most popular ways to battle the bug doesn’t do much more than make for pretty patio lighting.

COFFEE GROUNDS: I’d never hear about using coffee to kill mosquitoes but evidently there’s something to this. But to be clear, coffee grounds may work but studies about this bring up some big ‘buts’. A good article about this on the Modern Farmer website provides details. The bottom line, as cautioned by Modern Farmer is that even though coffee and coffee grounds may have a “significant effect on mosquito larvae”, there’s no research on how to deter or kill adult mosquitoes and, let’s remember–coffee is highly acidic. Even though coffee grounds are a terrific ingredient to add to your compost mix, the key word is “mix”. Pure coffee/coffee grounds alone added to your soil should only be used around plants that prefer acidic soil such as azaleas and rhododendrons, magnolias, hydrangeas, japanese anemones and blueberries.

BUG ZAPPERS: In another post published by the New York Times, research is cited that proves bug zappers do a great job of killing insects but, unfortunately, most of those killed are not mosquitoes.

They kill the wrong bugs. They are ineffective against mosquitoes and other biting flies, and their otherwise indiscriminate killing can disrupt pollination and generally throw the environment out of balance. Plus, the force of their electrocution can spew a mist of disease-ridden bug parts out into the air.

Research shows that a daily catch of insects by bug zappers over a season is comprised of only about 4% to 6% mosquitoes. The rest are potentially beneficial insects.

This unfocused insect elimination is so extreme that, according to the authors of the University of Delaware study, “Even if targeted biting flies were effectively controlled by electric zappers, the resulting destruction of thousands of parasitoids, predators, aquatic insects, and other members of the nocturnally active fauna would be difficult to justify.” University of Florida professor Jonathan Day told us, “We’re in a big enough crisis with colony collapse with honey bees that I think anything that impacts a beneficial insect population is problematic.”

Pond and irises
Mosquito heaven: Wild irises along the banks of a pond near Georgetown, Ontario.


CATNIP: According to research reported in ScienceDaily, the plant that trips out cats is also “about ten times more effect at repelling mosquitoes than DEET” due to an oil the plant produces called nepetalactone. Google catnip essential oil and a variety of vendors will pop up, including Amazon and Walmart (but read about my comments regarding essentials oils, below, first). I have to presume you’d have to grow a lot of catnip plants in order to get close to the same results as wearing the oil but, hey, catnip plants are lovely. Check out my post The Buzz On Catnip for some gardening ideas, including making a container planting combining catnip and lavender that’s as gorgeous as it is great for battling bugs.

Interesting side note: Research proves that catnip also repels cockroaches. Win, win!

SPATIAL LIQUID REPELLANT DISCHARGERS: No surprise that chemical repellants work. But how you use them can make a big difference in terms of effectiveness and comfort. According to the findings of more research conducted by The New York Times, battery-powered dischargers such as the Thermacell E55 work well at targeting mosquitoes over a large area and it’s silent and odor-less.

AND WHAT ABOUT ESSENTIAL OILS? There’s a lot of hype about how essential oils can be a great mosquito deterrent. One of the most popular is oil derived from the Lemon Eucalyptus Tree. Apparently, though, there’s a lot of confusion as to what’s what about this oil. I certainly was confused. As it turns out, there’s OLE which is Oil of Lemon Eucalyptus and then there’s Lemon Eucalyptus Essential Oil. Yup, there’s a difference. Research has proven that OLE can be beneficial at deterring pests. The jury’s still out on Lemon Eucalyptus Essential Oil. You can read all about this here.

The bottom line: Certain essential oils may have pest deterrent qualities but the fact is that, regardless of what plants the essential oils came from, all oils are highly volatile. What that means is that they evaporate quickly. Research has shown that you’d have to apply a lot of oil and do it very frequently in order to get anywhere near the same protection as a repellant containing DEET, for instance.


Goldfish: Your fine finny friends love mosquito larvae, so if you’ve got a water feature that includes still water, add some goldfish. Goldfish can also keep your rain barrel free of mosquitoes but rain barrels are not ideal goldfish homes on their own. You’ll have to take care of them and probably give them extra feed, just as you would if you were keeping them indoors in a tank. And forget it altogether if your rain barrel is a repurposed oak barrel once used to make alcohol.

Bats: Build a bat box and, hopefully, you’ll attract nature’s best mosquito consumer.

Fans: Get a long electric extension cord and haul your fan out onto the patio. Mosquitoes are really weak fliers. The force of the air current from a fan can very effectively ensure the critters can’t get anywhere near you. So aim that fake breeze right and crack a cold one. Cheer’s to a bite-free summer.

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