Muskoka mosquitoes and black flies: Don’t use a bulldozer when a fly swatter will do
By Chris Brew | June 20th 2026
At this time of year mosquitoes are out in full force. Muskoka residents and long-term visitors use several strategies to avoid them while enjoying the long summer days. The Muskoka room is a favourite — a screened area that makes outdoor living comfortable. Others use scented candles outdoors and keep insect-repelling plants like lavender and rosemary nearby. We apply personal spray protection to avoid itchy arms and legs. These do not have to be DEET repellents but made from essential oils like geranium or lemon eucalyptus.
Another strategy is to have licensed professionals fog your property with a broad-spectrum insecticide, permethrin, several times a season. So why not fog regularly? Isn’t permethrin essentially a synthetic version of the natural insecticides in the Chrysanthemum flower? Sometimes things are just too good to be true.
Permethrin is approved for use by Health Canada’s Pesticide Regulatory Directorate (PRD). Invented in the 1970s, permethrin is similar to the natural insecticides but designed to be more persistent. Depending on the isomeric ratio, it is also commonly more toxic. Mosquito and tick resistance will likely build with regular spraying. Permethrin kills all insects, not just biting insects and ticks, even the harmless, beneficial, and beautiful — the bees, dragonflies, cicadas and monarch butterflies.
The PRD has determined that, while nontarget organisms (birds, bees, aquatic life, even your cats) are at risk, that risk is acceptable when permethrin is applied in the approved manner. While birds can be harmed from feeding on poisoned insects, research has confirmed that permethrin can pass into developing eggs reducing fledgling survival. Fogging of your property commences in the spring when black flies and mosquitoes emerge, but also when birds are laying their eggs.
On your lakeside property also live small amphibians, like salamanders and frogs. Just parts-per-million of permethrin cause brain damage to their young. Permethrin is highly toxic to all aquatic life and the PRD requires that spray be kept away from water bodies. Yet, each time you have your lakeside property fogged, small amounts can drift to the lake. Here it settles in the sediment and can persist for up to a year. Microorganisms in the lake that play key roles in the food chain absorb it. In a study of effects on Monarch butterflies, University of Wisconsin’s Karen Oberhauser has found that even on a calm day the pesticide can travel over 20 metres. A moderately windy day, 120 metres!
In its 2023 Report Card, Muskoka Watershed Council reported on the evident deterioration of our natural environment, including the loss of biodiversity. Do we need to hasten this loss by fogging with permethrin?
Entomologist Doug Tallamy, professor of Agriculture and Natural Resources at University of Delaware, asks that you refrain from fogging insecticide. He offers a safer solution on his website. Muskokans know to empty any containes with water around their property for that is where mosquitoes breed, but Doug’s solution is counterintuitive. He uses their attraction for water as a trap! Water with a little organic material to assist in the fermentation process along with a small amount of a Bti mosquito puck will kill their larvae.
Let’s also think of neighbours. Many of us help our declining pollinators by planting gardens to attract them. Some spray drift to neighbours’ properties is inevitable. Health Canada’s PRD advises that it is good practice to warn your neighbours if you plan to spray so they can take precautions like close windows, cover outdoor toys and eating areas! Are you and your neighbours being warned whenever someone nearby is spraying this poison?
Please, stay cool this summer, and enjoy the best of what Muskoka can offer. But also be cool! Permethrin is “relatively” safe, but is that good enough? Nurture Muskoka, the choice is yours.
This article was first published by MuskokaRegion.com.
Chris Brew
This is article No. 25 in the current series, Nurturing Our Watersheds, from Muskoka Watershed Council. Its author is Chris Brew, BSc (Hons) in biology and chemistry, PhD in Science Education. Chris was introduced to Muskoka in 2001 and moved here permanently from Australia in 2009. She participated in the 2018 Federal Pesticide Regulator’s re-evaluation of permethrin, challenging their environmental risk assessment. The series is edited by Peter Sale.