It sucks and spits. How itchy it is!

Sssssuuuuuuuuumm, it passes by the ear of the person about to slip into a deep sleep, and again: sssssuuuuuuuuumm. A person is suddenly awake and goes on the hunt in a rage: if a mosquito ventures into the bedroom, it is usually their death sentence.

The relationship between humans and mosquitoes can at best be described as tense. Over the centuries and across all continents, these slender insects have been one thing above all else: a nuisance to humans. This is not only due to their penetrating buzzing, but also to the damage they cause. Their sting leaves itchy welts and, in the worst case, they inject us with a pathogen.

There are around 45 mosquito families. However, only three of them are blood-sucking and therefore potential carriers of disease: mosquitoes, midges and black flies. Plus the sand fly, which is the only species of butterfly mosquito that appreciates a sip of fresh blood. Humans are not the only victims of these biting midges; cattle, pigs, horses and dogs are also preyed upon. «Most mosquitoes are opportunistic,» says Alexander Mathis from the Vetsuisse Faculty at the University of Zurich, «they bite whatever comes in front of their proboscis.» Only mosquito species that do not occur in Switzerland, such as the yellow fever mosquito or the malaria-transmitting anopheles mosquito, favour humans as blood donors.

The following applies to all mosquitoes: The women are nasty. The men are vegetarians.

Mosquitoes dry out very quickly and have a relatively high evaporation surface due to their body structure. This is why they are mainly found near bodies of water and in warm and humid weather conditions at dusk. Because the larvae of the mosquito can only develop in standing water, they also lay their eggs near lakes, puddles and swamps. After one to three days, a larva hatches from the millimetre-sized eggs. After a further four to five days, it pupates and a few hours later the adult mosquito hatches. Their life is also short: the bloodsuckers usually only live for a few weeks, which is largely due to the external circumstances. In other words: too much sun or people who are too quick to react.

Mosquitoes are by far the family that most frequently feed on us. There are more than 3500 species worldwide, with just over 100 known in Central Europe. The same applies to all of them: the females are nasty. The males only fulfil mating purposes and are completely harmless. They while away the day licking nectar and honeydew or drinking the sap from plants that they pierce with their proboscis. While the males remain vegetarians throughout their short lives, the females give up this form of nutrition from time to time. The reason for this can only be approved of: they need nutrients for their offspring.
Iron and proteins from the stolen blood ensure that the eggs can develop after fertilisation. The caring mother draws two to eight millionths of a litre of blood per sting, which is manageable. It's not the blood loss that hurts us, but the mosquito spit. When the greedy female mosquito bites, she injects saliva into the victim via her proboscis. Why does the mosquito do this? An active substance contained in the saliva prevents the blood from clotting in the proboscis when it is sucked out, thus blocking it. The human body identifies the saliva as a foreign body and immediately begins to fight it: it itches and burns. This is unpleasant, but nothing more. «Real allergic reactions to mosquito bites are extremely rare,» says parasite researcher Mathis.

Sick from a mosquito bite? This is very unlikely in our latitudes.

Much more dreaded than a few itchy bites are diseases that can be transmitted by mosquito bites: Yellow fever, Zika, dengue and chikungunya fever, malaria, West Nile fever, Sindbis fever - the list is long. And yet there is no need to worry in our part of the world. Several conditions must be met for an infection with a pathogen to actually occur: Firstly, the mosquito must bite someone who is carrying the disease. It absorbs the pathogen with its blood. The pathogen multiplies in the mosquito's body and spreads from the intestine to other parts of the body - provided the external conditions are right: It must be permanently warm enough and the mosquito must live long enough.
Once the mosquito is actually full of the pathogen, it has to bite again to pass the disease on to humans with its saliva. «Even in highly endemic areas, only one per cent of mosquitoes usually carry the pathogen,» says Alexander Mathis. The probability of being infected by the few mosquito bites you get in this country is therefore extremely low. Even the Asian tiger mosquito, which has migrated from southern Europe in recent years and is now particularly widespread in Ticino, and which is currently causing concern among some, poses no danger. The populations are far too small and the often too cool climatic conditions make it difficult for them to survive.

Who the mosquito particularly likes to bite...

But why are you targeted by a mosquito in the first place? It is undisputed that not every human is equally attractive to mosquitoes, confirms Zurich mosquito researcher Mathis. However, science only partially understands the reasons for this. One important attractant is carbon dioxide, which is found in human breath. Other attractants are heat and special odours on the skin. Mosquitoes are also attracted to contrasts in brightness, but a rigid darkening of the bedroom does not necessarily lead to success: as body odour is the main deciding factor, a blood-hungry mosquito will find its way even without light. Female mosquitoes perceive human odours over a distance of up to 70 metres. «The different composition of the bacteria that help break down sweat creates a unique body odour,» says Mathis. Each species of mosquito has its own preferences: some like it when they can smell a lot of lactic acid aroma, others like a high ammonia content.

Scientists have now banished cheese feet, high cholesterol levels in the blood or certain eating habits to the realm of fairy tales as attracting factors. Women are also no more likely to be stung than men. However, current research suggests that metabolic products in the blood do have an influence. There are probably differences between blood groups, and pregnant women are indeed stung more often. Another group that is very popular with female mosquitoes still puzzles scientists today: People who drink beer and then go to sleep significantly increase their chances of being bitten.

And those who are immune to the stings...

Some people are bitten by mosquitoes but don't realise it. «They don't get pustules, they don't itch, they have become tolerant to mosquito saliva, presumably, for example, if they were bitten a lot as a child,» says Alexander Mathis. Such people then think they will be spared. They simply don't notice the bite. In fact, nobody feels it, the mosquito's proboscis is as fine as a hair. What we interpret as stinging pain is the body's immediate alarm reaction.

It bites to ensure its survival. It spits saliva so that its proboscis does not become blocked. We accept all that. But why this unspeakable whirring and buzzing? It's pure physics. When the mosquito flaps its wings, the muscles in its front body contract and relax again. This all happens at breakneck speed, causing the surrounding air to vibrate. This is how the buzzing sound is created, which incidentally is not only intended to deprive us of sleep: The mosquitoes recognise each other by it. Males buzz at a frequency of around 600 Hertz, females flap their wings a little slower and only reach 550 Hertz, so their buzzing is lower. The male mosquito finds this sexy. We rather less so. As soon as a buzzing buzzing buzzing buzzes us out of our dreams, it's time for the mosquito: Danger to life!
Picture: Fotolia

This protects against mosquito bites

• The most effective protection against mosquito bites is clothing.
• Free skin areas are best rubbed with so-called repellents. These are active ingredients that deter parasites by smell but do not kill them. The two best-known repellents are DEET and Icaridin. These artificially produced substances keep mosquitoes at bay for four to five hours, but can also irritate the mucous membranes and eyes. DEET is also suspected of being nerve-damaging under certain conditions; research into this is ongoing.
• An effective herbal repellent is PMD, also known as citriodiol. It also provides protection for several hours.
• Effective, but not very practical: lavender oil, coconut oil and other essential oils. Their protection only lasts for ten minutes, then they have evaporated and need to be reapplied.
• No matter what you rub yourself with: Every uncovered area of skin should get some, because the mosquito is meticulous.
• As the body's own odour attracts mosquitoes, it helps to wash yourself often. If you take a cold shower in the evening and then sit out on the balcony, you can rest for a while until your body odour and body heat are back to the level that attracts mosquitoes.
• Home remedies such as eating garlic, taking vitamin B tablets or placing tomatoes, basil plants and a lemon studded with cloves in the bedroom have yet to stand up to scientific scrutiny.

This helps with mosquito bites:

• Do not scratch! This is because scratching increases the blood supply to the affected area, the mosquito saliva that causes itching is spread further and causes even more discomfort. There is also a risk of dirt or bacteria getting into the bite site and causing inflammation.
• Temporarily apply ice cubes, cooling pads or cold flannels to relieve itching.
• If children just can't stop scratching, a cooling gel with cortisone can also be applied to prevent an infected wound. This soothes the itching even more effectively.
• Heat helps just as well as cold: a localised heat shock directly on the puncture site ensures that the anticoagulant proteins injected with the saliva are rendered harmless. Small heat plates are commercially available for this purpose, which heat up to just over 50 degrees Celsius. The whole thing also works with a coin that is heated over a lighter or a candle to such an extent that you can just about touch it. The heat shock works best directly after the sting, as the saliva is then still concentrated close to the surface.

The most dangerous animal in the world

Only one animal is deadlier to humans than humans themselves: the mosquito. More than 700,000 people die every year from a disease transmitted by these insects. The latest analyses even estimate up to 1.2 million malaria victims per year. By comparison, less than half a million people die from other people, 50,000 from snake bites, 1,000 from tapeworms and 10 are killed by sharks. The mosquito owes its danger to the fact that it is a valued host for some pathogens. This is how the viruses pass from person to person.

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