It’s summer — mosquito season in Canada.

I’ve been noticing a lot of signs advertising mosquito control services for homeowners. I decided to investigate further.

The services offer to spray your yard with a pyrethrin-based chemical in the places where mosquitoes hide. This is a bit misleading since mosquitoes breed in open water — mostly ponds and wetlands. However, they can be found in yard depressions or unscreened water barrels, if you have those.

I assume a small minority of yards have any type of mosquito breeding habitat. The mosquitoes may travel into your yard after spraying and may contract the pyrethrin on plants. I also assume that many of the mosquitoes are headed directly to open human skin and not nearby plants.

The Dark Side of Spraying for Mosquitoes

Now to the darker side of these sprays…. all the other things that are killed.

This is a list of species that are known to be killed by pyrethrin sprays:

  • Honeybees
  • Solitary bees
  • Fireflies
  • Spiders
  • Mites
  • Centipedes
  • Millipedes
  • Fish
  • Earthworms
  • Monarch caterpillars
  • A big shocker here…. CATS (they don’t have the enzyme to breakdown the pyrethroids)

This spray can last for up to 90 days killing off the insect life in your backyard. Which of course has a cascading effect on birds and wildlife who eat insects.

Some studies suggest this spray isn’t that effective. One group of mosquitoes, called Culex, are tree dwellers and are not affected by these sprays. The spray may only impact Anopheles and Aedes species of mosquitoes.

The Human Impact

These sprays are not harmless, as they may cause adverse effects like numbness, nausea or respiratory problems. Mice and rat studies suggest the chemicals do act on the nervous systems of mammals (Pitzer et al. 2021).

Also, keep in mind that mosquitoes are part of the food web and feed many species such as fish, turtles, bats and dragonflies. As pesky as they are, they are here to stay.

In summary, I would argue that these sprays are not as innocuous as they might seem, having many impacts on many species (including pets and humans) and to avoid applying these sprays at all costs.

May you have an awesome mosquito-free summer.

Learn more about mosquitoes >