Biologist Remco Suer believes he’s figured it the mosquito behavior, for his doctoral thesis at Wageningen University in the Netherlands. And the answer might help in the fight against malaria.

Previous research identified odors produced by 10 bacteria that live on human feet and that, in combination, are attractive to mosquitoes at close range. Suer's work shows that nine out of 10 of these odors are picked up by olfactory neurons under hairlike structures on the mosquitoes' mouthparts. Right nearby are some other key neurons—that recognize our CO2 from further away.