The Zzzz–zzZZZzzz–zzZZ sound that a mosquito makes while you’re trying to sleep isn’t the random modulation of a directionless insect. It’s the sound of a predator carefully circling its prey, smelling body odors and reading body heat, planning its strike.
Blood-hungry mosquitoes are females, on the desperate hunt for protein with which they can manufacture eggs. They repeat their hunt several times, making them dangerous vectors of disease. Their eggs will be laid in standing water before the female buzzes the last buzz of a short life as an airborne adult. Between the egg and adult stage comes the larvae, commonly known as mosquito wrigglers.
To find their prey, the female mosquito hones in on our smell. As they close in on their prey, they scan our body heat to help direct their strike.
That’s the conclusion of Dutch researchers, who set up a small wind tunnel with 3D tracking equipment and conducted experiments with hungry week-old female specimens of Anopheles gambiae, an African mosquito that hunts human blood and can transmit malaria. For some of the tests, the researchers placed a used sock at one end of the wind tunnel to gauge how they responded to human smell. In others, they placed a heat element at the end, set to 34°c to mimic the temperature of a human. Other tests involved using neither the sock nor the heat; and others used both. The researchers studied how the mosquitoes zeroed in on a specific point at the end of the wind tunnel under the different conditions.
Check out the following figures. Each row shows three views of the same wind tunnel experiments. The blue circles show the location of the plume of smell blown through the wind tunnel from the sock. The green lines track the mosquitoes approaching the end of the wind tunnel through the smell plume; red lines track the other mosquitoes. The target is at the center of the end of the tunnel.
“With heat alone, flights were … short and direct,” the scientists wrote in their paper, published in the online journal PLoS ONE. “The presence of human odor, in contrast, caused prolonged and highly convoluted flight patterns. The combination of odor+heat resulted in longer flights with more landings on the source than to either cue alone.”
So next time a mosquito is keeping you awake at night, don’t think of it as an idiot that’s buzzing mindlessly around your head. It’s just getting a good read on its prey before launching its strike.