There are around 3,500 mosquito species on Earth, and only a few dozen of them make our lives miserable. Of those, only the females bite: they need the protein in blood to develop their eggs. Males spend their short lives on nectar and never touch you.
How they find you
Three stages. First they detect the CO2 you exhale from tens of metres away. Then your body heat and moisture. Finally the chemical cocktail on your skin: lactic acid, ammonia, uric acid and the smell of your own skin microbiome. That is why some people seem to be magnets and others walk away untouched - sweat, recent exercise, alcohol, pregnancy and dark clothing all tip the odds.
The buzz is not a warning, it is courtship: wings beat 400-600 times a second, and a male can pick out the tone of a female of his species inside a swarm.
What the bite actually is
The "needle" is six needles: two to cut, two to hold and two to hunt for a vein. She finds one in about ten seconds, and while she does she injects an anticoagulant and a local anaesthetic, which is why you do not notice until she is gone. The welt and the itch are your reaction to her saliva, not the bite - so scratching only makes it worse.
What actually works
- DEET 10-30 percent, picaridin 20 percent, IR3535, or oil of lemon eucalyptus: the only repellents with serious evidence behind them.
- Screens and bed nets, ideally permethrin-treated.
- Loose, light-coloured clothing, long sleeves and socks.
- A fan: moving air breaks the chemical trail it is following.
- Emptying any standing water every 3-4 days. A bottle cap is enough to raise a brood.
What does not work, however well it sells
Repellent bracelets and ultrasonic gadgets. Vitamin B1 or eating garlic. UV bug zappers, which kill moths rather than the mosquitoes biting you. Citronella candles, which give you half a metre of protection at best.
One last thing: species do not bite at the same time of day. Aedes aegypti (dengue, zika, chikungunya) hunts by day, Culex (West Nile virus) at dusk, Anopheles (malaria) at night.
Mosquitoes kill more people than any other animal - over 700,000 a year through the diseases they carry. They are not a summer nuisance, they are public health.
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