By Eva Briggs, MD
In May I took a trip to the Adirondacks. Predictably, biting insects including mosquitoes were out and about. Some people in our group were attacked by those thirsty bloodsuckers more than others.
So why is it that mosquitoes preferentially bite certain people more than others?
Only female mosquitoes bite. They need the protein and iron in blood to help them grow and nourish their eggs. A mosquito’s mouthparts are surprisingly complex for such a tiny creature. The proboscis — that tube protruding like an elephant’s trunk from the mosquito’s face — has an outer sheath enclosing six needles. Two of the needles contain tiny sharp teeth that saw though skin. Two more needles spread the resulting opening apart while the female feeds. Another needle has sensors on the tip that allow it to seek out a blood vessel and poke into it. Then the mosquito uses this needle to suck your blood. One needle injects chemicals that prevent the blood from coagulating to keep it flowing. These chemicals irritate the skin causing the familiar itchy welts. While feeding, the mosquito extracts water from the blood and excretes it to enable her to pack in more of the nutritious blood contents.
When the mosquito injects irritating chemicals, she may also inject disease-causing microbes like bacteria and viruses. This makes the mosquito the deadliest animal out there, killing people with diseases like malaria, dengue, zika and various kinds of encephalitis.
What factors determine who is a mosquito magnet?
• Blood type is one factor determining who mosquitoes prefer. Their favorite is type O and least favorite type A. About 80% of people secrete molecules on their skin signaling their blood type. These secretors attract more mosquito than non-secretors.
• Carbon dioxide, a byproduct of metabolism that is exhaled with each breath attracts mosquitoes. They can detect it from at least 100 feet away with a specialized organ called the maxillary palp. People who produce higher levels of carbon dioxide draw more mosquitoes.
• Heat also attracts mosquitoes. Higher body temperatures appeal to mosquitoes. Sensors in the antennae detect heat. When scientists bred mosquitoes lacking a functional heat sensor it reduced their ability to find human prey. But that tactic isn’t fully protective since these biting insects use other methods in addition to warmth to locate victims.
• Pregnant women attract mosquitoes. Scientists believe this is because during pregnancy skin temperature rises and carbon dioxide production increases.
• Taste influences mosquito preferences. The chemicals produced in sweat and on the skin vary from person to person and mosquitoes find some individuals tastier than others.
• Drinking beer brings in mosquitoes. Scientists don’t know why.
• Skin bacteria vary from person to person. The type of bacteria and the amount present appear to influence mosquito preferences.
• Clothing color can affect mosquito feeding. At least that is something simple enough to modify. Mosquitoes prefer black, red and orange over green, purple, blue and white.
Mosquito control measures include eliminating sources of standing water and using insect repellents.
Eva Briggs is a retired medical doctor who practiced in Central New York for several decades. She lives in Marcellus.