Like flies, mosquitoes (Culicidae) are also two-winged insects (Diptera). The rear wings are bent back and help to stabilise and coordinate during flying. Mosquitoes’ bodies are only a few millimetres in length, they have fragile frames, long legs and are usually an discreet grey-brown colour. All mosquitoes need water for larvae to develop. Domestic mosquitoes can hibernate over winter in all developmental stages.
There are approx. 2,900 species existing worldwide, with approx. 50 of these being native species. The adults typically feature mouthparts which form into proboscis with only female mosquitoes actually only biting. Mosquitoes can be extremely annoying for humans and pose great medical risk, especially in the tropics, because they are vectors (carriers) of infectious diseases and parasitoses, such as Chikungunya fever, dengue fever and yellow fever (Aedes spec.), West Nile fever (Culex spec.) and malaria (Anopheles spec.). The Zika virus, which caused a stir particularly in Brazil in 2016, was transmitted by the Aedes species of mosquitoes.
Eggs are laid on water or close to water. Mosquitoes use their sense of smell to find suitable nesting areas but also recognise water surfaces through reflected polarised light. Eggs are laid individually on objects (Aedes, Anopheles) or as ‘rafts’ on water (Culex). The larvae that hatch typically move around in wriggling movements and mostly breathe (exception: Anopheles) through a breathing tube. Their main source of food is usually small particles. Pupae that form floating on the surface can also quickly dive using a projected, trumpet-shaped respiratory organ when they are disturbed. Completely developed insects can hatch out of pupae floating on the water’s surface in just a few minutes and are capable of flying in just about an hour.
The most significant behaviour of mosquitoes for humans is the sucking of blood. Only females drink blood during certain phases. The males get their nourishment from plant juices. Mosquitoes typically bite endotherms (‘warm-blooded’) animals (mammals and birds) but also ecotherms (‘cold-blooded’) vertebrates and also invertebrates. The process of finding a host is the subject of many research projects due to the significance it has on health as mentioned above. Temperature differences play a major role here, but differences in humidity, the presence of carbon dioxide from breathing, certain amino acids, lactic acid, octenol and hormones are also important.
When mosquitoes bite, they pierce the skin using their mouthparts and move them around until they find a blood capillary. They can suck blood up to a max. of 3 minutes. Saliva is injected into the skin while they suck to prevent blood from coagulating. Histamine contained in the insect’s saliva causes a bite to itch afterwards.
Mosquitoes tend to form noticeable swarms. The distance they fly from the ground and when they occur during the year and day is species-specific.
Various species of the genera Aedes (forest mosquitoes) e.g. Aedes communis: Aedes mosquitoes exist both in the tropics as well as in the Mediterranean and Central Europe. The different species measure 4 to 6 millimetres in size and are a plain grey-brown colour. In winter, the mosquitoes hibernate over winter as eggs which have been deposited on dry plants. They then hatch in spring when water levels rise. Usually only one generation of the domestic Aedes larvae hatches due to the fact that they require heat. The Asiatic Tiger mosquito (Aedes albopictus) is a carrier of Chikungunya and Dengue fever and was widely spread by humans. This species has existed in Europe since 1990. The Zika virus, which caused a stir particularly in Brazil in 2016, was transmitted by the Aedes species of mosquitoes.
Anopheles (fever mosquitoes) e.g. Anopheles maculipennis: These mosquitoes only occasionally occur in Central Europe and are mainly found in the tropics. They measure 4.5 to 7 mm in length. Their bodies are a dark-brown colour and their wings are spotted. The larvae require clean water in order to develop.
Culiseta and Culex (mosquitoes in the narrower sense) e.g. Culiseta annulata, Culex pipiens: The adults measure up to 10 millimetres in length and are a plain grey-brown colour. The larvae can also reproduce in small bodies of polluted water. It only takes two weeks for a generation to develop at optimum conditions (approx. 25°C), meaning that multiple generations can develop in one year.
Culex pipiens is the main carrier of West Nile virus (causes Encephalitis) which has been a serious health problem in North America since 1999. The change of the main host from the American robin (Turdus migratoris) to human in autumn when most birds migrate is important. Thus far West Nile virus has only occurred in isolated cases in Europe.
Mosquitoes can be prevented from appearing in homes by removing small bodies of water (e.g. water in flower pots, cover up rain barrels). Mechanical barriers (insect screens) on windows and doors can be used to prevent mosquitoes from invading homes. Electric vaporisers that release insecticides and insecticide sprays can also be used in some instances.
Covering skin from bites when out in the open offers protection. Insect repellents can be put on skin to protect uncovered areas.
Insecticides can be applied over large areas which naturally poses an ecologic problem. In biological pest control, protein crystals from Bacterium thuringensisisraelensis are applied to brooding waters. The otherwise non-toxic substance selectively kills insect larvae.