What an asshole. Credit: Wikimedia Commons

What an asshole. Credit: Wikimedia Commons

I’ve been engaged in an epic battle with mosquitoes for as long as I can remember. While every other kid was looking forward to summer, I could only shiver at the inevitable blisters my arms and legs would suffer.

My grandmother used to tell me I have “sweet blood”, which was very convenient for these tiny vampires. I cut candy out of my diet, but I still got bitten. Okay, so sweet blood is bullshit. But that still didn’t change the fact that I was targeted far more often than other people. Then I realized I wasn’t alone — apparently, I’m part of a select group of people listed on the mosquito’s menu as a delicacy. What’s your beef with us, you freakin’ mosquitoes?

Well, luckily I grew up to become a science writer. My forays confirm that mosquitoes are attracted to some people more than others. As to why, the jury isn’t out yet — there is a combination of factors that make me look like a light bulb for these bloodsuckers. The fact that there are over 3,500 species of mosquitoes, some varying in dietary choices more than others, doesn’t help, either.

Why mosquitoes want to suck your blood

First of all, it’s only the female mosquito that bites hosts. The benign males munch on flower nectar instead.

Female mosquitoes feed on blood, but not for their own nutritional purposes. After piercing the skin with its mouthpart, the hypodermic needle-like proboscis, the female mosquito starts sucking the blood out and into its abdomen. It is here that the blood is digested to produce eggs. They need the protein and other components in the blood to produce their eggs.

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In the United States, some 175 mosquito species have been identified, the most common of which are Anopheles quadrimaculatus, Culex pipiens, Aedes aegypti and Aedes albopictus. So, research that involves this mosquito species should be the most relevant.

First, we should start with what we know for sure: mosquitos, the females specifically, identify targets by sensing carbon dioxide. Why CO2? Because all vertebrates produce it, so mosquitos found being able to detect this chemical marker offered them an evolutionary advantage. Using their maxillary palp organ, mosquitos can ‘sniff’ carbon dioxide from as far as 150 ft (40m).

Right off the bat, this explains why mosquitos will come after you more frequently and in greater numbers when you’re exercising outside: you’re breathing harder and releasing more carbon dioxide than usual. Overweight individuals will also release more carbon dioxide because their bodies need more oxygen. Generally speaking, the higher your metabolic rate, the easier it will be for mosquitos to find you. This also serves to explain why pregnant women or people who drink alcohol attract more of the winged villains. For the same reason, adults are more prone to mosquitos than children, as are men more than women.

Of course, mosquitos rely on other cues as well besides carbon dioxide since living, blood-flowing vertebrates aren’t the only ones producing this gas (for example, mosquitos can’t bite trees). So to navigate and find a worthy host, mosquitoes also make use of visual markers. For instance, dark clothing is more attractive to the mosquitoes than the lighter kind. Besides coloring, mosquitos also use motion detection, so if you’re moving around an otherwise stationary environment you’re a sitting duck.

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Another marker is body heat. While CO2 tells the mosquito how to find you, your warmest parts of the body, which are also the most vascularized, tell the annoying critters where to bite. The most vulnerable body parts are the neck, inner elbow, backs of knees, armpits, and wrists.

There’s also evidence that suggests mosquitoes are attracted to certain smells. Among their favorites are lactic acid, ammonia, uric acid, carboxylic acid, and octenol (however, they seem to hate the smell of chickens). These compounds can be found in the sweat and breath. A 2011 study also found a few types of bacteria made skin more appealing to mosquitoes. The ankles and feet host the most robust bacterial colonies, which might explain why these are so prone to biting.

Finally, my grandma was half-right. Mosquitoes seem to be attracted to certain blood types more than others. Studies suggest Type O individuals are the tastiest. But ultimately, what makes some stand out more than others in the face of mosquitoes is governed by genetics. Joe Conlon, PhD, technical advisor to the American Mosquito Control Association, says genetics account for a whopping 85% of our susceptibility to mosquito bites.

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