What’s the first clue to a mosquito that there’s a human around? Elizabeth Tracey reports

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Mosquitoes, relative in size to people, are tiny. How is it that they can locate us so efficiently when they’re looking for a blood meal? Mosquito expert Christopher Potter at Johns Hopkins explains.

Potter: The first thing they use is carbon dioxide we give off in our breath. So we give off about 4% carbon dioxide every time we breathe and the atmosphere has .04% carbon dioxide and so that is an amazingly good indicator that there's a respiring animal thereby. They don't know what that animal is but they know that there's something interesting. That cue, because it can travel so far, let's say you're on like a American football field 100 yards, you could be on the goal line and a mosquito 50 yards or 100 yards away can actually pick up that carbon dioxide.   :31

Potter says mosquitoes aren’t very efficient flyers. They don’t make a beeline right for us, rather they gyrate around, continuously sensing the carbon dioxide and a number of other cues, until they’re just a yard or less away. Then they attempt to land and feed. Potter notes that breath isn’t something we can modify to keep mosquitoes at bay. At Johns Hopkins, I’m Elizabeth Tracey.