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Out for Blood

Bzzzzz…
There are 3,000 species of mosquito in the world: no matter where you go—mountain or valley, Timbuktu or Paterson, New Jersey—one of them is sure to find you. Last year, scientists isolated a mosquito that lives only in the London Underground: the subterranean version of a species that feeds solely on birds, it has evolved into a voracious biter of tube riders.

Although some species live as long as eight months, the life span of the average mosquito is two to three weeks. If it's any consolation, most mosquitoes will meet a violent end long before they have a chance to bite you—death by drought, death by barn swallow, death by windshield.

The Basics
You've got what mosquitoes need to breed: the protein in your blood is essential for their egg production. Accordingly, it's the female mosquito that bites you. Only she has the proboscis to plumb your veins; only she will inject a tiny amount of saliva (which later makes you itch) to keep your blood from clotting in her straw.

With every bite, she drinks five microliters of blood. At that rate, it would take roughly a million mosquito bites to suck your body dry. A mosquito takes at least one blood meal a week; she needs several days to digest, and another one to lay her eggs. Given her short time on earth, says Dr. Jonathan Day, a mosquito expert at the Florida Medical Entomology Laboratory, that's usually the end of her output. "If she can lay another batch, that's gravy."

Get Thicker Skin
Mosquitoes find the thinnest skin on your body, a knack aided by tiny sensors on their feet. And different species have different predilections. Some, like Psorophora ferox, a species common in New Jersey, attack the shoulders and above. Others, such as the ubiquitous Aedes aegypti, favor the backs of your ankles—making it harder for you to swat them. (Indeed, one study found that A. aegypti's preferred hangout is the underside of sofas. Another study, involving dirty socks and Limburger cheese, suggests that ankle-biting mosquitoes may actually be drawn to the smell of your feet—the more rancid the better.) And then there's Wyeomyia mitchellii, which prefers the tip of your nose. "It's a very small bug, it makes no sound, and its bite is initially painless," says Day. "You wouldn't believe the number of times I've watched one take a blood meal from a colleague who didn't even notice!"

Why Can't She Bite Somebody Else?
It starts with your breath. As you exhale, a trail of carbon dioxide wafts away from you like a ribbon; the lucky mosquito stumbles across it, then zigzags back and forth and zeroes in. As the mosquito gets closer, she picks up on other cues: a warm, sweaty body, dark clothes, and high concentrations of lactic acid (secreted in perspiration). In short, what makes you appealing (or unappealing) are mostly things you have virtually no control over. "Yes, some people are more attractive than others," says Jim McNeely, an entomologist at Rutgers University in New Jersey. "It's a function of body chemistry and body temperature." Indeed, experiments have shown that in a group of 10 people exposed to mosquitoes, three will be bitten many times, three won't be bothered, and the rest will receive only a bite or two.

What a Mosquito Calls Home
After she's had her way with you, a mosquito looks for a cool, dark, moist place to lay her eggs—puddles, swamps, salt marshes, tree holes. Some species are container breeders, preferring man-made receptacles such as flowerpots and old tires. American epidemiologists are currently monitoring the movements of Aedes albopictus, the Asian tiger mosquito, which carries dengue fever on its native continent. It reached the United States for the first time in 1985, arriving in a shipment of used truck tires. While the virus responsible for dengue has only just arrived, the mosquito has spread to more than two dozen states. It's a postmodern Gulliver, migrating on the wheels of yesterday's transport, coming to a backyard near you.

Shoo, Fly!
The cheapest way to fend off mosquitoes is to cover up: Wear shoes, long sleeves, and pants when outdoors, especially at twilight. Okay, that's no fun. Your next defense is repellents. "Natural" ones—extracts of citronella, prickly pear, or some other carbon-based life-form—work fine if you're game to reapply them every 10 minutes. Otherwise, stick to products containing deet. Check the label for the concentration: repellents with 10 percent deet are safe for children and will last two hours or so; you need the 100 percent solution only if you'll be in the woods all day.

As for those high-tech contraptions advertised in expensive catalogues, save your money. "Ultrasonic repellents do not work," McNeely says emphatically. If anything, these devices merely kill the insects that prey on those pesky mosquitoes.

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