200910 mozzie net

Why mozzies prefer some people to others

If you’re one of those unlucky people who get mauled by mosquitoes, it might be somewhat reassuring to know that scientists have spent decades trying to work out why the mini vampires love some humans more than others.

Key factors include carbon dioxide, body temperature and body odour, according to entomologist Matthew Bulbert from Australia’s Macquarie University – and perhaps not surprisingly, our microscopic bacterial friends seem to play an important role.

First, mosquitoes – insects from the family Culicidae – use their finely honed sense of smell to find their prey via carbon dioxide (CO2) emissions, which they can sniff out and track from up to 50 metres away.

From a distance, therefore, people who emit more CO2 are more likely targets. That can occur with higher resting metabolism or heavy breathing while exercising. As a generalisation, Bulbert says this could include men, adults and “full-figured” people or pregnant women.

Once mozzies get closer, they have thermal detectors that give them more clues – like Goldilocks, they won’t land if it’s too cold or hot but natural warm human body temperature is “just right”.

Credit: James Gathany / Flickr

When it comes to body odour, it’s well known that mosquitoes are attracted to different scents.

Anophele mosquitoes are attracted to smelly Limburger cheese, for instance. These mozzies are the same ones that love biting people’s feet and ankles, and it turns out the bacteria used to culture the cheese are the same that cause foot odour.

In other research sweat from volunteers was sterilised and mosquitoes showed no interest. However, adding bacteria turned on their attraction.

“So from this there was the suggestion that whatever bacteria were doing was being detected by the mosquitoes,” says Bulbert.

In fact, it’s currently thought that bacterial diversity – which seems to be key to good health all round – could explain why some individuals are more susceptible, he adds. “The more diverse, the less attractive.”

Among their multitude of activities in the body, microbes help remove waste products that are secreted onto our skin, suggesting mosquitoes may have evolved a mechanism to tap into the bacteria’s activities.

So how do tasty people avoid getting bitten? They can surely be given credit for trying.

A survey identified 167 different strategies, including eating garlic, avoiding bananas, using topical repellents (even cigarette butts soaked in alcohol), burning animal dung, drinking gin and tonic, avoiding alcohol, and spraying diesel and Windex.

A popular strategy is use of vitamin B, ingested or via skin patches, but research suggests this doesn’t work.

However, with any of these studies, Bulbert notes they don’t consider mosquito diversity – more than 3500 different species have been described so far – so research on one species doesn’t necessarily apply to all of them.

Indeed, different species have their own idiosyncratic preferences, which may have to do with survival.

“If you consider the human body as a niche just like a tree, you have some animals that prefer tree trunks, some the canopy, others the roots, and selecting different regions reduces competition,” says Bulbert.

“Presumably this is also the case for mosquitoes. It’s known different regions of the body may have different skin micro flora and this can be distinguished by the different species of mosquitoes.”

As a rule, using essential oils or other fragrant substances topically might mask the scent or reduce secretion of the body’s waste products, but Bulbert says their effect is limited. Citronella is considered effective if applied but the candles don’t seem to repel mozzies and may even lure them.

Many animals, including insects, birds, bats, lizards, amphibians and fish, eat mozzies so you could try getting creative by installing a pond with frogs, for instance, but bear in mind that still water is a breeding ground for mosquito larvae so any water features should have moving water.

Ultimately, it’s important to take the threat of mosquito bites seriously in areas where they carry life-threatening diseases. And although this applies to less than 2% of species, there are fears that climate change is making their spread more likely.

The best approach, Bulbert says, is to cover up during periods when mozzies are most active, such as dusk, or in places where they’re most prolific, such as wetlands. Failing that, he recommends using well researched repellents such as DEET.

High airflow is another possible strategy – although they’re good flyers, mozzies don’t fly well in the wind so fans could be a helpful deterrent.

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