Are mosquitos more active in moonlight? Some facts to help you avoid them

TORONTO -- Today is World Mosquito Day, which means it’s time to celebrate some facts about one of the most hated insects of all time.

These tiny bugs are capable of wreaking havoc of all sizes, responsible both for the small, itching bites that follow us every summer as well as the spread of numerous deadly diseases.

August 20 was christened “World Mosquito Day” because this was the day that Sir Ronald Ross confirmed Patrick Manson’s theory, in 1897, that mosquitos carried the malaria parasite.

A “mosquito” is not a single insect, but is in fact the name for a group of insects. There are thousands of different species of mosquitos, sorted into genuses.

According to the Medicines for Malaria Venture’s website, around 40 species of the mosquito genus Anopheles can transmit malaria to humans.

Around 80 different species of mosquitos live in Canada -- 64 species co-existing in Ontario alone -- and their bites can produce different levels of pain in the victim. Only the female mosquitos suck blood.

But one of the strangest facts about mosquitos is that they share a similarity with another (albeit fictional) bloodthirsty creature: like werewolves, they bite more during the full moon.

Dr. Mireille Marcotte, National Manager of Plant Health Surveillance with the Canadian Food Inspection Agency (CFIA), said in a CFIA podcast that “scientists haven't determined the reason yet, but studies show that mosquitoes are more active during the full moon. In fact, they can bite up to 500 per cent more.”

One study from 1975 found that on the full moon, light traps set out to catch mosquitos recorded increased activity during moonrise and in the middle of the night.

Apart from staying indoors when the moon is full, how can you avoid mosquito bites?

Not all mosquito repellants -- whether they be sprays, wearable devices or natural products billed as repellents -- are made equal.

One study that looked at the effectiveness of 11 different spray-on and wearable repellants in 2017 for repelling specifically the Aedes genus of mosquitos found that spray-on repellants “containing N,N-Diethyl-meta-toluamide and p-menthane-3,8-diol had the highest efficacy in repelling mosquitoes.”

They tested five wearable devices, and found that only one which released Metofluthrin was effective -- on OFF! brand clip-on device.

Citronella candles had zero effect when it came to repelling mosquitos, the study said, despite popular opinion.

A study that looked specifically at candles found that if you want to light a flame to get mosquitos away, you will have more luck with a geraniol candle, which repelled mosquitos and sand flies at five times the rate of a citronella candle.

Another study testing repellants found that repellants based around natural ingredients provided less than three hours of protection, on average, and the inclusion of essential oils as an ingredient did not seem to provide any benefit.

Geranium, cedarwood, clove and peppermint oils were found to repel mosquitos for over an hour, but only at 100 per cent concentration.

Repellants containing DEET have also been found to be effective in other studies.

However, some people might just be more attractive to mosquitos naturally.

Several studies have suggested that people with blood type O are more likely to attract mosquitos. One study from 2004 found that mosquito species Aedes abopictus landed on people with blood type O 83 per cent of the time, as opposed to only 46.5 per cent of the time for people with blood type A.

One pilot study from 2015, which looked at how attracted mosquitos were to identical twins versus non-identical twins, also found that genetics themselves might play a role in who mosquitos are more likely to chomp on.

The study pointed out that while differences in body odour have long been known to affect whether or not a mosquito finds you attractive, the why of body odour hadn’t been looked at very closely. There is a genetic component in a person’s natural scent, and people who are less attractive to mosquitos produce their own natural repellents.

Although genetics, moonlight and repellent effectiveness still need to be studied more, there is at least one foolproof way to avoid mosquitos: swat them before they get you!