Here’s what you need to know about mosquitoes this summer


Have you ever noticed that some summers seem plagued with mosquitoes, while others aren’t? Do you feel personally attacked by mosquitoes year after year? It’s not just in your head. Mosquito numbers vary from year to year, and month to month. And yes, some people attract more mosquitoes than others! We spoke to experts who gave us the buzz on the most annoying (uninvited) guests at your summer BBQs.



 

 

 

When is mosquito season?

In Canada, mosquito season typically starts as early as May and dissipates by late August. 

Mosquito larvae develop in temperatures between 7 and 16 degrees Celsius. In Canada, that means April and May. Canada sees the most mosquitoes in June. It’s the sweet spot because larvae develop in spring, and continue to multiply throughout the warm season. Scorching July heat can thin out mosquito populations, and by the end of August, mosquitoes enter “diapause”. That’s the stage in their lifecycle when they are busy laying eggs that will lay dormant all winter, and female mosquitoes enter hibernation themselves. 

Why are mosquitoes worse some years than others?

Researcher Jamie Heal at the University of Guelph’s School of Environmental Sciences told us that mosquito populations vary year-to-year depending on the weather.

Most species of mosquitoes lay their eggs around the edges of temporary or semi-permanent ponds and puddles every summer. In the winter, snow protects the eggs by offering insulation from the extreme cold. Come springtime, the melting snow provides the perfect aquatic habitat for mosquito larvae. 

Longer winter seasons that leave melting puddles of water on the ground well into spring, contribute to higher levels of mosquitoes. Mosquitoes like it warm and wet, so any drastic temperature changes, like a snap freeze in the spring or a hot, dry spell in summer, can negatively affect their population.

Heal also noted that their temperature preference “is why mosquitoes bite the most after the sun goes down, when it is cooler and humidity goes up”.

Will this year bring more mosquitoes than other years?

Experts maintain there is no foolproof method to accurately predict mosquito numbers. Winter 2019 was for the most part average in terms of temperature and snowfall, and we’ll definitely see the usual surge of mosquitoes in May and June. The rest of the season will depend on what summer weather is in store.

Should we be worried about West Nile Virus?

Besides being annoying little blood suckers, mosquitoes carry viruses and diseases like West Nile, Zika, Yellow Fever, and Malaria. West Nile Virus is the most pervasive mosquito borne illness in Canada. It first appeared in Ontario in 2001. Since then over 5,000 humans have been infected in Canada. Luckily 80% of those infected are asymptomatic and less than 1% of those infected experience dangerous neuro-invasive symptoms.

Cold winters typically prevent serious epidemics of mosquito borne diseases in Canada. But thanks to climate change, that may not always be the case. As the winters become milder, species of mosquitoes that would normally die out, are able to survive the winter and establish populations in a new location.

Since 2016, both the yellow fever mosquito and the Asian tiger mosquito were found in Southern Ontario. Fortunately, neither tested positive for viruses.

How can we escape mosquito bites?

Mosquitoes lay their eggs in stagnant water, so it’s a good idea to empty and refresh things like rain buckets and birdbaths to prevent mosquitoes from breeding in your own backyard. 

The best way to protect against bites is to use a topical insect repellent that contains DEET, Picaridin, or Oil of Lemon Eucalyptus. Dr. Cameron Webb (Medical Entomologist, NSW Health Pathology) told us, “It is important to remember that the concentration of the repellent will determine how long you’re protected from bites, not how many mosquitoes are kept away. This means that a lower dose repellent will work just as well as a high dose repellent over short periods of time”. Just remember to reapply!

Are there effective alternatives to topical repellants?

Citronella candles, mosquito repellent patches, and wristbands do not provide adequate protection from mosquitoes, and bug zappers can actually draw in more mosquitos and other flying insects, like moths.

You may have heard the popular myth that eating things like onions and garlic will keep mosquitoes away, but Webb wants you to know, “there is no scientific evidence that anything you can eat or drink will protect you from mosquito bites!”

If you react negatively to topical repellents, the best thing to do is to wear loose, light coloured clothing with a tight knit that covers as much skin as possible. Also, avoid going outside in the evenings when mosquitoes are at their peak!

Is it true that mosquitoes bite some people more than others?

You’re not imagining it! Heal says, “Yes. In all my years testing mosquito repellents using human subjects, I found significant differences in attractiveness between people. Some studies have shown that chemicals emitted from the skin from different people vary and therefore affect attractiveness. But in my experience other factors are much more important. Mosquitoes are attracted to carbon dioxide, motion and heat. … Bigger people exhale more CO2, are a bigger visual target and give off more heat. Smaller people exhale less CO2, are a smaller visual target and give off less heat. The other factor is a subject’s behaviour. People that talk more and are hyperactive attract more mosquitoes because they give off more heat, are a better visual target and give off more CO2. People that are quiet and stand statue-like attract fewer mosquitoes because less heat, less of a target and less CO2.” 

Are mosquitoes even necessary to our ecosystem?

Sorry to all the haters, but the answer is yes. Heal reminds us that, “[Mosquito] larvae are food for fish, frogs and some other aquatic insects. The adults get eaten by bats and some birds (eg. swallows).” Keep in mind there are over 2,500 species of mosquitoes in the world, and 10 in Canada. Of those 10, only 5 feed on human blood. Also, did you know only female mosquitoes feed on blood? Male mosquitoes never touch the stuff. They don’t even have the ability to bite. Instead, they feed on nectar from flowers. Females need the protein from blood for egg development. 

Mosquitoes are an unfortunate annoyance on summer evenings, but hopefully knowing a bit more about them will help you hate them less. At the very least you’ll be able to protect yourself! Good luck!

Resources:
Algonquin Park. Mosquitoes and Black Flies. Retrieved from http://www.algonquinpark.on.ca/visit/park_management/mosquitoes-and-blackflies-(biting-insects).php

CTV Television, Inc. (2013). The buzz on mosquito season.  Retrieved from https://search-proquest-com.qe2a-proxy.mun.ca/docview/1407006112?accountid=12378

Giordano, B. V., Kaur, S., & Hunter, F. F. (2017). West Nile V irus in Ontario, Canada: A twelve-year analysis of human case prevalence, mosquito surveillance, and climate data. Retrieved from http://dx.doi.org.qe2a-proxy.mun.ca/10.1371/journal.pone.0183568

Harbach, R.; Besansky, N. (2014). Mosquitoes. Retrieved from https://www-sciencedirect-com.qe2a-proxy.mun.ca/science/article/pii/S0960982213011949

Heid, M. (2018). DEET Is the Most Effective Bug Spray. But Is It Safe? Retrieved from http://time.com/5347546/is-deet-safe/

MacMillan, H. (2018). Why your summer might be full of mosquitoes, according to a scientist. Retrieved from https://theconversation.com/why-your-summer-might-be-full-of-mosquitoes-according-to-a-scientist-98369

World Health Organization. Climate Change and Human Health. Retrieved from https://www.who.int/globalchange/climate/summary/en/index5.html

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