Mosquitoes

Biology of mosquitoes

There are currently 51 species of mosquitoes (Culicinae) in Germany (including two exotic mosquitoes such as the Asian bush mosquito (Aedes japonicus) and the Asian tiger mosquito (Aedes albopictus)). The most important mosquito species in Germany can be roughly classified as follows:

  • The so-called flood mosquitoes (genus Aedes)
  • The Culex and Culiseta mosquitoes, the best known species are Culex pipiens (the common house mosquito) and Culiseta annulata (the large ring mosquito)
  • The fever mosquitoes (Anopheles species), which used to transmit human malaria in Germany
  • The waterbed mosquitoes (Coquillettidia richiardii), which mostly occur on lakes surrounded by reeds


The flood mosquitoes

With 28 species, this genus accounts for more than half of all native mosquito species. Floodwater mosquitoes are particularly prominent among mosquitoes due to their mass and nuisance-inducing occurrence. The meadow and floodplain mosquitoes(Aedes vexans, Aedes sticticus and others, known as "Rhine snakes" on the Rhine) are particularly important in many areas of the temperate zones due to their mass occurrence in summer months with high water levels. Their breeding areas are usually temporary bodies of water in the floodplain of medium-sized and larger rivers and lakes with fluctuating water levels, e.g. on the Rhine, Elbe, Danube, Altmühl, Nidder, Chiemsee or Lake Constance, which are plague-inducing mosquito species.  After hatching as flying insects following a flood, the male mosquitoes form dancing swarms and attract the female mosquitoes with their flight frequency. The females are seized by a male and mated while flying. After mating, the females need a blood meal to complete egg maturation. The egg yolk is formed with the blood. The male mosquitoes do not bite, but feed on sugary liquid, similar to the females when they are not producing eggs. The females of some floodwater mosquitoes can migrate many kilometres (e.g. Aedes vexans >10 km) in search of a host.

After the blood meal - they often suck on humans, but can also be animals - they sit in a quiet place for about four days to mature their eggs. They then fly to their "birthplace" and lay their eggs in the damp soil of the depressions that were recently flooded during high tides. After about 4 days, the larvae have developed in the eggs. They can hatch from the eggs at the next high tide if the water temperature is above 8 °C. However, they can also lie in the ground for several years (> than 5 years) until they hatch during flooding. The larvae in the egg cases are resistant to drought and cold. In autumn, the larvae in the eggs enter a hatching inhibition. While the flying insects die in autumn, only the larvae in the egg cases of the meadow and alluvial forest mosquitoes overwinter.


Forest mosquitoes (e.g. Aedes cantans, Aedes punctor, Aedes communis and Aedes rusticus) are also floodwater mosquitoes. Their breeding grounds are usually swampy woodland areas (e.g. alder swamp forests), where water-filled forest ditches and forest ponds form as breeding grounds after the snow melts and after rainfall in spring. The larvae of forest mosquitoes hatch at water temperatures above 1 °C and emerge as larvae early in the spring (some species, e.g. Aedes rusticus , can also emerge as larvae in winter). The flying insects hatch in April and May. The forest mosquitoes are usually only a nuisance in the forest and at the edge of the forest. They do not migrate as far as the meadow and alluvial forest mosquitoes (maximum 2 km).


Furthermore, the two exotic mosquitoes Aedes albopictus, the Asian tiger mosquito, and Aedes japonicus, the Japanese bush mosquito, belong to the flood mosquitoes because they lay their eggs above the water body and the larvae only hatch from the eggs when the water level rises (e.g. after rain or filling up a container).

Information about the Asian tiger mosquito and the Japanese bush mosquito

Culex and Culiseta mosquitoes

Of the six species represented in Germany, the best known and most common species of this genus, Culex pipiens, usually lives in the vicinity of human settlements, where it can become a nuisance in buildings, which is why it is generally referred to as the "house mosquito".

House mosquitoes are very much crepuscular and nocturnal animals and migrate very little. They therefore usually only bother humans in the evening and at night in or near buildings. During the day and in the open countryside, they are usually less of a nuisance. As with other mosquitoes, only the females suck blood, the males feed on plant sap.

House mosquitoes overwinter as mated females, in contrast to the flood mosquitoes(Aedes species), which overwinter in the egg stage. They seek out their winter quarters in late autumn, where they are protected from severe frost and draughts and where there must be a relatively high level of humidity. They mainly hibernate in old cellars with clay floors (but not in the heated or dry cellars of modern houses), sewers, well shafts, agricultural buildings, garages, garden sheds, earth tunnels, etc., where they sit on ceilings and walls. More rarely, they hibernate outdoors, e.g. in brushwood piles or animal burrows (see picture: hibernating mosquitoes).


In spring (usually in April), the females leave their winter quarters and soon start laying eggs. Each female usually lays several hundred eggs in a package (the so-called "boat") on the surface of the water. House mosquitoes are not very choosy when selecting their breeding sites. Basically, any non-flowing or slow-flowing body of water that exists for more than 2 weeks is suitable. Small and very small bodies of water, such as rain barrels, cesspools and sewage pits, soakaways, sewers, gullies, garden ponds with rotting plant material (without fish and other predators), water-filled old tyres and tin cans, sagging or blocked gutters and rain puddles are particularly favoured. In areas infested with the Asian tiger mosquito (Aedes albopictus), developmental stages of both species can be found in water bodies with little organic pollution.


At water temperatures above 10 °C, the larvae hatch from the eggs a few days after they are laid. No changes in water level are necessary for the larvae to hatch, as is the case with the Aedes species, for example, as the Culex females lay their eggs directly on the water surface. There are also 4 larval stages which, depending on the temperature of the breeding waters, are passed through in a total of 1-3 weeks; higher temperatures accelerate development, lower temperatures delay it. The subsequent pupal stage lasts 2 - 4 days, depending on the temperature. Larvae and pupae are similar in appearance and lifestyle to the corresponding stages of the floodwater mosquito. The flying insects hatching from the pupae mate after a few days. After a few more days - after a complete blood meal - the females begin to lay their eggs. As the entire development period (from egg laying to egg laying of the next generation) is only about 3-5 weeks (again depending on the temperature), there can easily be 4-5 generations in a normal summer and even 6-7 generations in a warm summer. Due to the high number of eggs and the short generation time, a single overwintering female can have many millions, theoretically even many billions of offspring during one summer.



The large house mosquito "Culiseta annulata":


The representatives of the genus Culiseta are mostly large and powerful mosquitoes. The best known and most common species is Culiseta annulata. Its way of life is comparable to that of Culex pipiens, the common house mosquito. This is why it is also known as the "large house mosquito" or, because of the white rings on its legs, the "ringed mosquito". Its wings are spotted with scales. Culiseta annulata is often confused with the Asian tiger mosquito because of the white rings. However, the ringed mosquito is significantly larger and does not have such contrasting black and white scales.

The fever mosquitoes

Anopheles mosquitoes are the sole vectors of human malaria, which is why they are also known as fever or malaria mosquitoes. Although there are eight Anopheles species in Germany, there have been no known cases of malaria in Germany for decades.

Eight Anopheles species are found in Germany. These are Anopheles messeae, An. maculipennis s. s., An. daciae, An. atroparvus, An. claviger, An. petragnani, An. algeriensis and An. plumbeus. The females of Anopheles plumbeus can cause considerable localised infestations in rural communities. They often breed in open cesspits. The females also sting during the day, usually in the immediate vicinity of the breeding waters. They usually migrate less than 100 metres. This species is also a competent vector for Plasmodium falciparum, the causative agent of malaria tropica.

The waterbed mosquitoes

In Germany, this genus is only represented by one species, namely Coquillettidia richiardii. The larvae and pupae of this mosquito live permanently submerged until the flying insects hatch. They meet their oxygen requirements by boring into the aerial tissue(aerenchyma) of plants with their respiratory tube or respiratory horns. Favoured plants are Glyceria, special sedge species or bulrushes(Typha). According to its way of life, Cq. richiardii colonises permanent plant-rich waters, such as oxbow lakes or siltation zones of lakes. The dirty yellow coloured Coquillettidia females lay their eggs directly on the water surface, where they are glued together to form roundish egg boats. After a few days, the young larvae hatch, which immediately bore into aquatic plants. They overwinter mainly in the third larval stage. The flying insects hatch in early summer. Coquillettidia has only one generation per year. The females can be very troublesome in areas with many permanent bodies of water with reed or bulrush growth.

General information on the biology of mosquitoes

All mosquitoes depend on standing water for their development. Basically, almost any standing body of water, with little or heavy organic pollution, can be used as a breeding ground. This includes temporary flood waters along rivers and lakes or ponds and pools rich in plants, but also many small and tiny bodies of water, such as water barrels, water-filled flower vases, drains, cesspools, old tires, tree hollows or splash holes. In the body of water, the mosquitoes develop through four larval stages and a pupal stage to become flying insects. Development in water depends on temperature; higher temperatures accelerate development.

What all mosquitoes (often called "gnats") have in common is the possession of a proboscis, through which the mosquitoes can easily separate themselves from similar-looking but harmless two-winged insects, such as: B. allow the chironomid to be distinguished.

However, only the proboscis of the female mosquito is equipped with functional stinging bristles and is therefore suitable for sucking blood from humans, mammals or birds. The blood meal is necessary for the eggs to mature and thus successfully produce offspring. The male mosquitoes also have a proboscis, but this only serves to take in exposed liquids, such as sugary plant juices (nectar), as food. So only the female mosquitoes bite. They can also feed on sugary liquids, but without then forming eggs.

The female mosquito's stinging proboscis consists of six stinging bristles and the lower lip. During the blood meal, only the stinging bristles are pierced into the skin. First, the female mosquitoes are attracted to their host by chemical stimuli, especially odors, such as: B. the carbon dioxide in the air we breathe and sweat with its ingredients (butyric acid, amino acids and nitrogen compounds). At a closer distance, the temperature radiation and the moisture release of the host body are also perceived. To a lesser extent, optical stimuli (recording the host's movement in the area) also play a role, but contrary to popular belief, bright light is more repelling than attracting mosquitoes. The female mosquito flying towards a host sits on the skin and first touches the surface of the skin with the tip of the lower lip, on which a number of sensory hairs are located. With the sensory hairs that respond to temperature, smell, taste and touch stimuli, the mosquito recognizes blood vessels running under the skin, which generate an increased skin surface temperature at this point. The mosquito bites there, but often only finds a blood capillary after several attempts.


When a mosquito bites, a saliva secretion is released through a channel in a bristle. This secretion contains proteins that inhibit blood clotting, for example, and histamine, which causes a small inflammation. Pathogens contained in the saliva secretion can be transmitted when the mosquito bites, particularly in the tropics. The mosquito uses a pumping device in the area of the front digestive system to suck blood into its intestines through a channel in the upper lip until the intestines are so full that the mosquito's abdomen swells up extremely from the blood it has absorbed and turns red.


The mosquito then pulls out the stinging bristles and often flies away with difficulty due to their heavy weight. It then uses the protein-rich blood food to further develop its eggs. The biting process usually lasts around 2 minutes, sometimes longer. The mosquito takes in around twice its body weight in blood (2-3µl).

Egg laying

There are sometimes considerable differences between the different mosquito species in the way they lay their eggs and in the way they look. The native flood mosquitoes (Aedes/Ochlerotatus species) lay their eggs individually in moist soil. With a length of just under a millimeter and a diameter of around 0.3 mm, they are just barely visible to the naked eye on a white background. The eggs are heavier than water and do not float. The larvae can only hatch when the eggs are submerged by flooding or heavy rain. By developing in floodwaters that only contain water for a short time, the larvae evade the fish, who are effective predators and cannot find a habitat in the temporary waters.

The females of the genera Culex, Culiseta, and Coquillettidia glue their eggs together to form so-called “egg boats” directly on the surface of the water. A Culex pipiens clutch usually contains more than 300 eggs and is over 5 mm long and 2-3 mm wide. The egg boat of Culiseta annulata looks similar, but its eggs are slightly larger. After one to two days of embryonic development, the larvae hatch directly into the water body.

The Anopheles females lay their eggs individually on the water surface by releasing the eggs one by one above the water surface.b. Equipped with swimming chambers, the eggs float on the water surface until the larvae hatch.

Mosquito larvae/pupae

Mosquito larvae:

The body of the mosquito larvae consists of a head with eyes, antennae and mouthparts, as well as 3 fused thorax and 9 abdominal segments. In Aedes, Ochlerotatus, Culex and Culiseta, there is a strong breathing tube on the 8th abdominal segment, which the larvae use to hang on the water surface to breathe.

The larvae of the Anopheles species do not have a breathing tube; their breathing openings lie flat as a "breathing plate" directly on the back of the 8th abdominal segment. Due to the formation of this breathing plate and fan-like branching hairs all over the body (palm leaf hairs), the Anopheles larvae lie horizontally on the water surface. Due to their horizontal position, the Anopheles larvae can largely escape the reach of the fish, whereas the larvae of the genera Aedes, Culex and Culiseta hang on the surface of the water with their breathing tube so that their head and body point diagonally downwards.

The breathing tube of the larvae of the aquatic mosquito Coquillettidia richiardii differs greatly from the original shape because it has a special sawing device for drilling into plant tissue.

Mosquito pupae:

The head and chest of the pupae have grown together to form a more or less pear-shaped complex in which the limbs of the future flying insect, such as wings, legs, antennae and proboscis, develop, embedded in sheaths.

The pupa stores air under the wing and leg sheaths, so that, unlike the larvae, it is lighter than water and usually hangs on the water surface. Two respiratory sacs serve as respiratory organs and for attaching to the water surface. There is a pre-formed seam between the respiratory sacs in the middle of the front body, which bursts open when the future flying insect hatches from the pupa.

The long, narrow rump with 8 abdominal segments and two leaf-shaped appendages, called rudders, is placed on the underside of the forebody when at rest.

When the water surface is disturbed, the pupa strikes with its abdomen and oar plates and flees into the depths, only to then slowly rise back to the water surface due to the air deposits.

Unlike the larvae, the pupa no longer takes in food, as the future flying insect develops inside it. This means that pupae cannot be killed with a toxic feeding substance (e.g. with Bacillus thuringiensis israelensis (BTI) preparations) like the larvae.

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