What attracts mosquitoes to us? We are bitten by the females, who need the proteins present in our blood for the maturation of their eggs, while the males only bite the plants.
Can we somehow make ourselves “unattractive” or, better yet, “invisible” in the eyes of these odious insects that infest our summer nights (and not only)? As far as the first question is concerned, science gives us a lot of information. For the second, the answer is NO: mosquitoes have everything they need to find us, such a quality of detection and reaction systems that rivals the most sophisticated computers connected to the most powerful robots, all managed by a brain that is more or less as big as the point that closes this sentence.
Infallible radar systems
Sui maxillary palps (protrusions of the head similar to antennas) of the mosquito are located specific receptors of carbon dioxide, capable of smelling up to 164 meters away. Just breathe and then emit carbon dioxide so that this little cloud of gas disperses into the air, and some particles reach the “nose” of a mosquito, triggering a burst of nerve impulses in your brain: you have been intercepted.
Once the carbon dioxide has been identified (which alone is not enough to find you, otherwise it would fly directly into your mouth, a situation so bothersome to you as useless for them), the mosquito shifts its attention to the visual characteristics of the environment. It does not follow fashions: it always prefers dark and red colours.
The Caltech experiment
To test this, Caltech researchers (California Institute of Technology) let females fly freely in a light-colored wind tunnel, except for a single dark square on the floor at the end of the tunnel. Initially, mosquitoes flew without paying any attention to the floor; as soon as, however, the experimenters were introduced into the CO2 tunnel, the insects began to inspect the dark box, flying over it for hours, at a height of a couple of centimetres.
In the Caltech experiments, to “land” in the right place, the mosquitoes at this point used chemical compounds and heat emitted by the target. What attracted them most were hot objects with a high degree of humidity, such as sweaty skin. This explains why overweight people (have greater oxygen/carbon dioxide exchange), pregnant women (producing more CO2 with breathing than average and their body temperature is higher) are more “appetising”, sports types (during exercise they sweat and get hot, and lactic acid also forms in their muscles, which mosquitoes smell), beer drinkers (it is not clear if it depends on ethanol or the fact that alcohol increase body temperature).
Mosquitoes prefer blood from group 0 and are also attracted to skin bacteria, which would explain why they bite us especially at the extremities. Feet, hands and face, in this order, are the areas preferred by mosquitoes for their “banquets” precisely because it is here that colonies of bacteria harbour. Finally, according to Jerry Butler, a forensic entomologist at the University of Florida, “people with high concentrations of cholesterol or steroids on their skin attract more mosquitoes“.
It seems that a mosquito can also do without any of its tools and still be able to find you without major problems. Wearing light clothes, for example, serves to neutralise only one of their many detection systems, extraordinarily and annoyingly effective, but not to counteract their sensory powers. Even if you hold your breath to keep it from “sniffing” the CO2, they would still be attracted by the warmth of your body, as long as they fly close enough. If then next to you there is a friend (who breathes!), in no time at all, the mosquito will sting you both (preventing your friend from breathing is equally useless). If you give off heat, you are sweaty (which is taken for granted in these days of unbearable sultriness) and maybe you wear a dark garment, you are doomed! Put a stone on it!