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Insect plague (in Finnish: räkkä)

One of the nasty things in light northern summers is the insect plague, mass occurrence of blood-sucking insects. Mosquitoes, black flies, horseflies and biting midges all of them appear almost at the same time and tease as well as man as animals and get them very restless and even upset. In south where the summer is longer there isn’t this kind of a mass occurrence but all those insect groups appears there at their own time.

The insects of this plague seek blood, which is their nutrition and cause itchy, sometimes inflaming bump in the sting or bite spot. At their worst for example mass occurrences of black flies can cause a death of a reindeer calf. The insect plague collects reindeer in to herds and they escape the plague to snow splotches of fells or to hot sand slopes in forests and to roads. There warm currents lift excreting smells which attract the plague insects up to the sky and that relieves reindeer quite a lot. See reindeer!

Only female insects suck blood, males use nectar from plants. Mosquitoes have stinging other plague species have dagger-like mouth parts.

Mosquitoes lay eggs in to wetlands and larvae develop in standing waters. Most of the species overwinter as eggs, only few species grow up already in the autumn and overwinters as an adult and they also occur immediately in the spring when the weather warms up.

The larva of black fly lives in streaming waters and pupas attach for example in to surface of stones. Horsefly females lay eggs in to leaves of aquatic plants and larva live in the bottom mud or in wet soil. The biting midge larvae usually eat rotting matter.

Mosquitoes (Culicidae)

The most annoying acquaintances in the midsummer of Lapland are mosquitoes that, along with other insects of the insect plague, find their victims for sure. The smell is what helps them to find their target, and therefore, a hurried hiker will draw a swarm of mosquitoes into himself/herself. Air temperature, humidity and carbon dioxide content (the gas that is created in breathing) influence as a smell mark in the search of food.

Although there are about 40 species of mosquitoes in Finland, there are no more than some ten species that torment people. Only two of these (Aedes communis and A. Punctor) form the main part of the pests in the southern Finland. In the northern Finland, a third northern mass species, (A. Pionips), will join them. There are more species in the southern Finland than in the north but the individual numbers are considerably larger in Lapland. There are plenty of suitable wetlands, bogs and puddles, and the moisture conditions of the early summer are almost always favourable for the development of the mosquito. It has been discovered that there exists only one generation of each species during the summer but because the occurrence periods of different species follow one another, i.e. are hardly ever simultaneous, it seems as if there were new generations following one another all through the summer.

Most of the mosquitoes overwinter as eggs in wetlands where the female has dropped its eggs on the previous summer. The larva that develops from the eggs in the spring when the snow melts, is a real water dog that often rises to the surface of the water to take oxygen from the air. In a good three weeks, the larva develops into a pupa, from which a mature mosquito hatches out after a few days and takes wing. During the whole of this time, development progresses in standing water, and therefore, most of the mosquito larvae die in the middle of their development when the puddles dry up during the dry early summer.

However, there exists a small mosquito species (Culiseta) that torment people. Mosquitoes in this species mature in the late summer and the matured ones that have been overwintering appear in the air very early in the spring. They might even show up at the same time when snow melts in patches, long before the mass occurrence of the other mosquitoes. Nevertheless, the actual mosquito season in the north does not start until the mid June with an annual slide of week or two depending on the weather conditions of the spring.

Only the female mosquitoes suck blood because they need the nutrients of blood for their efficient egg laying. The males suck nectar so they search for their food mostly from flowers.

In Finland, both the genera of Culex and Anopheles consist of only a few species. According to their name, Culex-species (in Finnish: lintuhyttyset) suck blood mostly from birds. In addition, Anopheles-species (in Finnish: horkkahyttyset) are not dangerous to humans but very annoying because they suck blood during the night and they like it inside buildings. In Finland, there has been no sign in nearly a hundred years of them carrying the parasite that causes malaria in warmer countries. Instead of that, other mosquitoes in Finland may carry pathogenic organisms, among others infectious tularaemia.

Black flies (Simuliidae)

One of the reasons for the northern insect plague is small black flies that resemble flies but belong to mosquitoes. They torment people in thick swarms usually during warm weather at streaming waters and also often on the shores of lakes and on bogs. Females force their way under the clothes, suck blood and cause a small red spot to develop on the skin around the biting area. This spot will start to itch very much during the hours after the incident. As in mosquito species, only the black fly females suck blood and their early development takes place in the running water but unlike mosquitoes they develop in streaming waters. Nevertheless, after the mature black flies have hatched out, they may fly far in the inland, for instance if they follow reindeer herds.

There is close to 50 known black fly species in Finland but only a dozen of them suck blood from humans. With its sharp oral parts the female cuts a wound into the skin and sucks the blood oozing out of the wound and uses it as a nutrient. At the same time, the female secretes fluid from its salivary glands. This prevents blood from coagulating and causes the red spot that develops around the wound.

The females lay their eggs in running water. The larvae that develop from them attach by their rear end to the stones and plants at the bottom. With their special head fans, their filtering device, the larvae filter micro-organisms and small decayed particles from the water as their nutrients. They get the oxygen through their skin from water. When pupating, the larva weaves a cocoon attached to the base. The cocoon is shaped like a slipper and often characteristic of the species. The pupal stage itself has bushy respiratory filaments that stick out from both of its shoulders. As the pupal is ready to mature, a gas bubble will develop under the pupal skin. With the help of the bubble, the mature black fly bounces to the surface and immediately takes on wings. Sometimes when the water in rivers drops, one can find dead larvae, pupae and empty cocoons in masses attached to the stones along the shores.

An early nuisance for both humans and animals is Simulium ornatum, which has received its Finnish name (koreamäkärä) due to its colourfulness. Sometimes during the hot spells in May it shows up already after the middle of May. The smallest black fly species is Simulium pusillum (Finnish: tundramäkärä) which is slightly bigger that the biggest species of biting midges. During the haymaking, they may gather into a big swarm that torments people. Usually the black fly species appear one after another. Usually the black flies produce only one generation in a summer but in hot summers there is, for instance, a second generation of Simulium ornatum.

Biting midges (Ceratopogonidae)

Along with mosquitoes and black flies, an essential part of the northern insect plague is their smaller relatives, biting midges (Ceratopogonidae). Perhaps due to their size of one millimtere or two, they find easily their way to skin through (?; under) the clothes and cut tingling wounds with their tiny knifelike jaws in order to suck blood from their prey. – they force their way to skin through the clothes and cut tingling wounds with their knifelike jaws in order to suck blood from their prey. It is not always possible to find the cause of the sting; you only feel and you have to look very sharply will to reveal the malefaction. People are blessed with probably a good ten species of them. Familiarity with the group is not very good yet.

Biting midges show up usually as the last parties of the insect plague (Finnish: räkkä), long after the midsummer. It is often August which is the festive time for the biting midges but it can go on until the berry season of September. Like black flies they bite firmly on the sweat spots, such as wrists and ankles, on the skin, but they may also “invade” eyes. Being briskly insects, the biting midges, unlike some other insects of the insect plague, do not shun a person who has spread insecticide on his/her skin.

The biting midges spend their larval stage in water systems, damp soil - even in moist conditions below the earth’s crust, and in fungus. There are a good 70 species known in Finland, but the living habits of many are still unknown. However, it has been found out even now that there is quite a lot of variation in living habits.

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