Europe is now an unwilling host to invasive mosquitoes that can transmit dangerous diseases. DW looks at how to treat and avoid their bites, how to stem their spread, and the latest scientific research.
Bzzzzzzzz. Ouch! Slap! Gotcha, you little pest! Aha, a normal mosquito. It has no conspicuous black and white pattern, so fortunately it is not an Asian tiger mosquito or an Asian bush mosquito, which have now been detected in many parts of Europe, including Germany.
What makes the Asian tiger mosquito so dangerous?
Worldwide, there are more than 3,500 mosquito species, of which approximately 50 are also native to Germany. All of them are annoying, but not all are as dangerous as these three immigrated species: the Asian tiger mosquito (Aedes albopictus), the Asian bush mosquito (Aedes japonicus, also called the Japanese bush mosquito) and the Korean bush mosquito (Aedes koreicus).
That is because these invasive mosquito species can transmit more than 20 types of virus, including those that cause dengue fever, chikungunya fever, yellow fever, West Nile fever, and the encephalitis and Zika virus.
The symptoms of these diseases are often initially similar to a flu-like infection, with high fever, headaches, aching limbs and weakness.
The three types of mosquito are easily confused. With the black Asian tiger mosquito, the white striped hind legs and the white line on the body and between the eyes are particularly noticeable. The other two tend to be dark to black-brown in color, and have striking light horizontal stripes on the body and legs.
These mosquito species, which originally came from Southeast Asia, have been introduced into various regions in North and South America, Africa, the Middle East and Europe in the last decades. Their spread results from global travel and the worldwide transport of goods.
How do I treat tiger or bush mosquito bites?
The Asian tiger mosquito bites mainly during the day in the morning and evening hours, and preferably outdoors . As with other mosquitoes, only tiger mosquito females suck blood. That is because to be able to reproduce, they need proteins, which they get through blood. It is of no importance to them whether it is animal (from mammals or birds) or human blood. They cover their other energy needs with nectar and plant sap, just as male mosquitoes do.
The bites of the tiger and bush mosquito are not more painful or worse than those given by the native mosquitoes. At the site of the bite, there is some reddening and swelling, and the skin itches.
These skin reactions are triggered by the saliva secretion that the mosquito injects, which is meant to stop the blood clotting. The body reacts allergically to the proteins in the saliva and releases the hormone histamine.
Even though mosquito bites can drive you crazy, you should not scratch them. Doing so will only make the anticoagulants in the saliva spread further, making the bite itch even more. It could also make it easier for germs to penetrate the skin. If the area is already scratched open, put a sticking plaster over it. Then no germs can get in, and you will not scratch any further.
Cool the bite
Cold water or even your own saliva will help to relieve the itching and swelling as a first aid measure. Then cool the bite with ice cubes or cooling packs, with ointments or creams or with one of the many tried and tested household remedies such as halved onions or potatoes, a slice of lemon, vinegar or curd cheese — simply use whatever is available.
Heat the bite
This recommendation may sound like a contradiction to the last, but in fact, it is not. If you heat the bite to over 51 degrees Celsius (124 degrees Fahrenheit) for a few seconds, you may be able to decompose parts of the mosquito's saliva along with the histamine produced by your own body. This can slow down the swelling and speed up the healing process. There are battery-powered devices available in pharmacies that heat a small ceramic plate to the necessary temperature for three to six seconds. The sooner the device is used after the bite, the greater the chances of success.
Watch the bite
Cooling and not scratching helps with all mosquito bites. After two to three days the swelling should go down. However, if the mosquito bite becomes very large and feels hot, this may indicate a more serious allergic reaction or infection.
It is possible that the scratching has allowed germs to enter the bite, or the mosquito itself may have transmitted some bacteria or viruses. This can be very dangerous, especially with the Asian tiger and bush mosquito. So if the symptoms persist or others, such as fever, occur, you should see a doctor.
How do I prevent tiger and bush mosquito bites?
The way tiger mosquitoes eat and mate depends particularly strongly on their sense of smell. Body odor, breath, sweat and perfume attract mosquitoes, especially outdoors. If you have a cool skin from a cold shower and do not use strongly scented shower gels, perfumes and cosmetics, you will probably not be bitten as often.
The substance diethyltoluamide, which is contained in most insect repellents, also blocks the mosquitoes' sense of smell. Diethyltoluamide makes people almost imperceptible to mosquitoes so the insects bite less often.
Of course, long clothing also helps, especially if it is light-colored: Most mosquitoes avoid pale fabrics since they can hide better on colored or dark ones.
Why do some get bitten more often than others?
Mosquitoes are generally very picky. Some people get bitten very often, others barely at all.
One reason for this is the individual scent profile, which differs from person to person. It is composed of metabolic products with different smells, such as lactic acid, fatty acid, ammonia or carbon dioxide, which are released through the air we breathe and through sweat. These attract mosquitoes in different ways.
In 2015, a research team from the London School of Hygiene and Tropical Medicine concluded that pregnant women and obese people with a higher body temperature are bitten more often.
It is still unclear whether blood type is another decisive factor. In 2004, Japanese researchers found that people with blood group O were bitten twice as often as people with blood group A, but the study was not really conclusive because only 64 people took part.
Tackling tiger mosquitoes with science
Male Asian tiger mosquitoes live only about 10 days, females about six weeks. During this time, the female produces on average more than 300 eggs.
In 2016, an expert commission was set up at the Friedrich Loeffler Institute, the German national animal health research center, to look at mosquitoes as vectors of pathogens. Its aim is to develop recommendations for monitoring and controlling mosquitoes.
Researchers in Germany are also testing the use of sterilized males. Here, the slightly smaller larvae of the males are sorted out with a fine sieve and then sterilized using gamma rays.
When the females mate with such a male, they become pregnant but do not produce viable offspring. In the summer of 2016, the first sterilized males were released in Germany, and the hatching rate has now reportedly dropped by 15%.
How can I prevent the spread of tiger and bush mosquitoes?
After two dry summers in a row with significantly fewer mosquitoes, the alternation of humid and hot weather in Europe and Germany this year has produced very favorable conditions for the insects, says Doreen Werner from the Leibniz Centre for Agricultural Landscape Research (ZALF) in Müncheberg near Berlin. "However, their occurrence varies greatly from region to region," says the biologist.
Where heavy rainfall has caused water levels to rise, for example along the Oder on the German-Polish border or at Lake Starnberg and Ammersee in Bavaria, there is a real mosquito plague, she says. According to Werner, the warm temperatures also are also shortening the time the mosquitoes need to develop.
Mosquitoes love warm and humid conditions, which is why ponds and other bodies of water in gardens offer them ideal conditions for producing offspring.
As with all mosquitoes, tiger mosquito females like to lay their more than 300 eggs just above the water level in places where small amounts of water gather. Garden ponds, knotholes in trees, clogged gutters, drains, rainwater barrels, plant pot saucers and old car tires are all ideal.
There, the tiger mosquito eggs can survive dry and cold periods for months. If the water level rises at some point, due to rain, for example, it triggers the hatching of the mosquito larvae.
So if you make sure you do not have any places where shallow water can collect, and if you empty gutters, rainwater barrels, bird baths and pot saucers regularly, then you are not offering the tiger mosquito and other mosquitoes a habitat for laying eggs.
Some plants also ward off mosquitoes naturally, because mosquitoes cannot tolerate their smell. These include tomato bushes and walnut trees. So they provide a nice, environmentally friendly alternative to insecticides.