From the steamy sub-tropics of New Guinea to jungles on the Indian sub-continent and even in the temperate forests of Scandinavia, sipping a cleansing ale or G and T while watching the sun go down is a rite of passage for travellers across the globe.
And being outside in the evening and sipping your favourite tipple brings its own risks, usually in the tiny form of a blood-sucking mosquito.
But here’s something only a very few of us have considered – not only does drinking alcohol help attract mosquitoes in the first place, but the alcohol in our blood may also give them as big a buzz as it does us.
Quite few years ago, when I was trekking in the steamy Rwenzori Mountains of Uganda, I set off on a day-long quest to find a group of elusive Mountain gorillas. At the end of what turned out to be an exhausting six-hour marathon that traversed valleys and perpendicular slopes so frightfully steep as make a grown man weep, I fell, sweaty and exhausted, on to the nearest patch of grass.
As a microscopic amount of strength returned to me, I was given and, with extraordinary effort, opened one can of cold beer. I drank it. I felt good. Then I opened another. And then, as some of the pain and lactic acid started to seep from my overused and wearied arms and legs, yet another.
I had no idea just how elusive mountain gorillas could really be, or how physically demanding it is to chase them.
The afterglow of that encounter – made when we finally caught up with about a dozen gorillas of assorted sizes and ages as they made their sleeping nests for the night – ended with me and my adventurous friends sipping yet more cold beer beside a campfire long into the night as we relived our great achievement.
And, at last, when we had all told each other outrageous lies about how brave we all were, a couple of us decided it would be a clever idea to sleep by the fire in canvas decks chairs.
Many hours later, I awoke to the following sudden and painful scientific discoveries:
- There are large and ravenous populations of mosquitoes even in the mountains of Uganda.
- Clothes do nothing to protect you from a voracious mosquito’s bite.
- A human being drinking alcohol outdoors at night is, to every millions of mosquitos for kilometres around, the equivalent of sounding the dinner gong to begin the festival of blood.
As a result, my arms, legs, and torso resembled a mixture of raspberries and yoghurt – large red lumps against a creamy white background.
I can assure you that was not the stand-out memory I was expecting to take home with me.
However, as I discovered much later, and as noted in the Journal of the American Mosquito Control Association, 2002, human beings dramatically increase their likelihood of becoming a mosquito meal when they drink alcohol outdoors.
The study this revelation is based on only had 13 participants, but it showed those who had downed a bottle of beer were more likely to have mosquitoes land on them to feed.
However, precisely why mosquitoes appear more attracted to drinkers remains a mystery. What we do know is that mosquitoes around the world home in on humans using two chemicals that we exhale as we breathe.
These are carbon dioxide and octanol. Octanol is a secondary alcohol contained in human exhalation. Octanol is also known as “mushroom alcohol” because it is the compound that helps give mushrooms their unique taste.
And this is where my own imagination began to take over. It occurred to me that a mosquito that drinks my alcohol saturated blood may get drunk, too. It is, despite the multiple billions of mosquitoes who have fed on drunk humans over millennia, the subject of little research.
Entomologist Tanya Dapkey, from the University of Pennsylvania in Philadelphia, recently told the BBC that: “I suspect the answer is no, because the blood alcohol level is going to be so low.” But go searching for reliable scientific study about mosquitoes and alcohol, and the juice gets a little thin.
“A lot of the adult insects have a crop which stores all of these juices they take inside and then gradually releases them,” says Erica McAlister, a senior curator of insects at London’s Natural History Museum. “Enzymes break everything harmful – like alcohol and bacteria – down.”
Erica, who wrote the book The Secret Life of Flies, has some previous experience of the effects of alcohol on fruit flies, including the common fruit fly or, as it’s sometime called the “vinegar fly”. These tiny insects have a powerful taste for alcohol-laden rotting fruit.
“I don’t know if mosquitoes get drunk, but we see it with fruit flies,” Erica says. “They do get drunk, but they do have exceedingly high tolerance. In smaller doses they get very hyperactive – and flirty. And they get less choosy about their partners as well. Give them a larger dose and they just pass out.”
Sound familiar? Briefly, fruit fly lose their inhibitions and start to get down and dirty. They might as well open a nightclub, too.
Like their lush and loose fruit fly cousins, mosquitoes are also partial to rotting fruit, which creates alcohol as the sugars it contains ferment.
Only females feed on blood to get the protein needed to create eggs. Males and females also feed on nectar produced by flowers – mosquitoes are important pollinators – and use the sugar it contains for energy to survive. This nectar can also sometimes ferment into insignificant amounts of alcohol.
So there you have opportunity and a little motive, the essential elements in pinning any crime on a perpetrator.
“The idea that alcohol makes us more attractive to them is an interesting question to me,” says Tanya Dapkey.
And here’s why. Some of us are genetically predisposed to being more attractive to mosquitoes. As much as 20 per cent of humans carry these traits. One is your blood type. For example, people with Type O blood are twice as likely to be bitten than those with other blood types, according to one study.
Other risk factors are those who have a high body temperature, pregnant women (possibly related to body temperature), those who exhale heavily (putting out more carbon dioxide), and larger people.
Mosquitoes are also choosy about where they bite you, depending on the species that’s doing the biting. Some blood bandits prefer your legs and feet, while others are more likely to gravitate to your neck and face, possibly because they’re homing in on carbon dioxide emissions from your mouth and nose.
But here’s the sting in tail for those of us who choose to imbibe outdoors. The ethanol that we give off in our sweat when we have been drinking may be the chemical signal behind the findings of that tell-tale scientific study in 2002.
A similar project in 2010, this time with 18 participants in Africa’s Burkina Faso (just north of Ghana and the Cote d’Ivoire), also found mosquitoes were attracted to those who had been drinking. The ethanol in the alcohol you’re drinking – and that you are excreting in minute quantities through your sweat – may be signal to the biting insects that there’s a meal nearby.
“The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes,” the Burkina Faso report said.
“If you’re hungry and you’re walking around,” says Tanya Dapkey, “the thing that’s more likely to make you go in one direction than another is the smell of food.
For example, let’s think roast beef. That strong distinctive smell of moist roasting beef may well be the bell that rings your culinary gong and starts you salivating. And even if roast beef isn’t your thing, then it can start you thinking about what you might really like a bit (or bite) of.
As any gourmand will tell you, alcohol works in an equivalent way. That why we have aperitifs – to get our gastric juices flowing, our saliva saliving (yeah, I know that’s not a word but what the heck) and sharpen our appetites for the meal to come.
Think of the ethanol being secreted in your sweat when you are drinking beer on a summer night = hear that dinner bell ringing yet? Well, it’s a good bet the mosquitoes do. Considered with the other factors that might attract mosquitoes your way, simply avoiding a drink is unlikely to take you off the menu –
Your genetics probably have a more influential role in determining that.
So, here’s the dilemma. Drink a cold one on a hot night and feel good but get a few extra mosquito bites. Or don’t drink a cold one on a hot night, don’t feel quite so good but also get bitten by mosquitoes. Well, I know which side of that argument I come down on.
And there’s always the helpful chance that if you drink enough beer, you won’t feel anything at all, at least until the next morning. And I happen to know that is a verifiable, unassailable fact.