​​​​​​​​​​​​​​​​​​​​​​Common critters infographic
Dr. Keystone says mosquitoes, ticks and flies are three of the most common insects Canadians should look out for this summer. (Graphic: UHN)

For many Canadians, warmer weather means more time outside.

But more time outside means more opportunities to be bitten by insects and other creepy crawlers, whether you're enjoying the sun in the city or at the cottage.

In this three-part series, Dr. Jay Keystone, a physician in the tropical disease unit at Toronto General Hospital, UHN, breaks down how to recognize different bites and what you can do to treat them.

Today, he discusses mosquitoes. Next week, flies and ticks are on the agenda.


Where to find them: Mosquitoes are common across Ontario, in both urban and rural settings.

What are the symptoms: Mosquito bites cause minimal redness and swelling, and are less painful than most other insect bites. The most noticeable symptom of a mosquito bite, according to Dr. Keystone, is itchiness.

"The itch that you get really comes from the saliva of the mosquito," says Dr. Keystone.

"It's also used as an anticoagulant that allows the blood to keep flowing so the mosquitoes can continue to draw blood."

mosquito Icon
  • Found in both urban and rural areas
  • Bites cause red, itchy bumps on the skin
  • Use insect repellent to prevent bites
  • In Ontario some carry West Nile
  • If you experience flu-like symptoms see a doctor​

What are the risks: While being bitten by a mosquito in Canada doesn't put you at risk for Zika virus, it's possible for bites to lead to West Nile virus.

Common West Nile symptoms include fever, headache, rash, muscle aches and pains, according to Dr. Keystone. In some cases the virus could lead to severe neurological problems, including paralysis and septic meningitis.

However, according to Dr. Keystone, fewer than 20 per cent of people who are infected with West Nile actually get sick, and severe neurological symptoms most often affect the elderly or those with underlying conditions.

What you can do: There are a number of ways to reduce the itchiness associated with mosquito bites. Dr. Keystone says one way to do so is using your finger nail to make a cross over the swollen area. He also recommends benzocaine, an over-the-counter local anesthetic, after bite or topical steroids to help soothe itchy bites.

Dr. Keystone says a small number of people may experience a moderate allergic reaction after being bitten by a mosquito, resulting in a large, red, swollen area with itchiness. In this case, he recommends taking an antihistamine.

If you've recently been bitten by a mosquito in Ontario and are experiencing flu-like symptoms, seek medical attention immediately.

Want to know more? Stay tuned for next week when Dr. Keystone will discuss flies and ticks.

Fly Icon
  • Mostly nuisance
  • Watch for flies at the cottage or other rural settings
  • Common flies include black-flies, deer-flies, stable-flies and horse flies
  • Bites are bigger than mosquitoes' and have a dark centre
  • Use ice to relieve particularly swollen or paintfull bites​​
Tick Icon
  • Most common along the southern border of Lake Ontario
  • Perform tick checks regularly
  • Use tweezers to carefully remove ticks, making sure to remove the head
  • If you find a tick after 36 hours, you may be at risk for Lyme disease
  • Use insect repellent and wear long sleeves to prevent bites​​

Part Two: Dr. Keystone breaks down what you need to know about flies.

Part Three: Learn how to prevent and treat tick bites this summer.​​

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