Каминяр Дмитрий Генаддьевич: другие произведения.

The Common Mosquito And The House Fly. Horseflies And Botflies.

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   The order of the Diptera (which includes mosquitoes and flies) is relatively young among the insects. The earliest finds of the extinct flies belong to the Jurassic, about 150 MYA. Their rise began with the expansion of flowering plants and mammals throughout the planet. The mouths of the Diptera are built so that they can feed only on liquid food: flower nectar and animal blood.
   Around 85--100 thousand Diptera species are known to science. They are called so because only their front pair of wings is developed and used in flight.
   The malaria mosquito, whenever it lands upon anything, raises its belly, while the ordinary mosquito keeps its belly horizontal, or even lowers it a bit.
   The larvae of the common mosquito hang at the water's surface vertically, upside down, while those of the malaria mosquito - horizontally.
   Both insects belong to the family of the real mosquitoes that has 1500-2000 members. From the tundra to the tropics the members of this family can be met and everywhere they are the most intolerable of all the bloodsuckers. However, not all of the real mosquitoes suck animals' blood; many species are satisfied from nectar and plant juices. And even among the bloodsuckers only the females feed on blood, the males drink only the plant juices.
   By autumn, all of the common mosquito's males perish, only the females' winter in various cracks. In spring they wake up and rush to the water. They lay eggs on the water's surface, and the eggs float in small clumps around 7 millimetres in diameter, and each clump has several hundred eggs. If for some reason the female mosquito was unable to drink blood before laying its' eggs, then lays fewer eggs - 40-80.
   The larvae hatch soon enough. They're heavier than the water and to stick to its surface they must undertake serious effort: by twitching and bending they rise above and hang upside down at the film at water's surface. But if some danger appears, they immediately sink below. Then they swim upwards once again. They feed on microscopic algae, the remains of the deceased animals and plants, filtering during 24 hours about a litre of water each.
   Approximately after three weeks the mosquito larvae pupate. The pupas are lighter than water and rise to the surface naturally. They already have eyes, although they are hidden beneath the pupa's shell. But this shell is transparent and sudden illumination frightens the mosquito pupas - they all immediately sink into the depths. But soon they surface back. The pupas don't eat anything: their mouth parts are transforming from filtering to blood-sucking ones. Other transformations occur quickly as well, and within several days a long-legged, winged mosquito appears from inside the burst pupa.
   The mosquito males gather into swarms during quiet, windless evenings: usually they hover around some tree, bush, bell tower, even a person walking along a road. Turning the heads against the wind, the mosquitoes dance at that spot, rhythmically flying up and down. The smell that is emitted by the mosquitoes' special glands during the dance is increased a thousandfold when they are swarming. While dancing, the mosquitoes spread it in all the directions, and, attracted by that smell, the females gather to these dances from all of the sides. Sometimes they too gather into a swarm that hovers slightly below the dancing males. Suddenly one or another female breaks away from the swarm and flies upwards into males' company. A moment and the mating couple lands on the ground.
   How the male finds the female so quickly among thousands of relentlessly scurrying up and down mosquitoes? It hears the female! The male hears the beating of its wings. They vibrate 500 times a second and the male's antenna began to vibrate in unison with them. A special organ, located in the second sector of the antennae, records only the beating of a sexually mature female's wings. Specifically a sexually mature, a sexually immature female beats the wings in a different rhythm, just as the mosquito males do. Therefore the mosquito's antennae, aimed at a particular rhythm of vibrations, do not react to the wing swings of the other males in a swarm. An old question: to lay mature eggs, all of the mosquito females must drink blood beforehand - is not finally solved. Apparently, for some subspecies of the common mosquitoes, it is not necessary. The hungry females develop eggs too, only their fertility is far less than those who drank blood.
   The house fly. It doesn't live in the wild countryside, beyond towns and cities. It became ma's companion. Its larvae develop in all sort of rotting refuse. The fertility and virility of these flies are amazing. The female lays 100-150 eggs every 2 to 4 days (just 5-6 times during her life). Within approximately 12 hours or 24 hours headless larvae hatch from them. Within 24-36 hours they pupate for the first time, then more and more. Within less than 10 days they pupate. If it's warm, then in three days, if it's colder, then it takes them a day or two more to transform from a pupa to an adult fly. Within three days of maturing it is laying eggs already.
   In this manner, one fly generation is capable of developing and beginning to reproduce within approximately 2 weeks. And apparently that during a hot summer one fly can produce nine generations of its kind. Let's allow that all of its descendants have survived, and then their number by the end of summer will surpass 5 trillion! 70 flies weigh apparently one gram, while the descendants of a single fly - 80 thousand tons!
   A colossal distributer of germs! For each fly bears upon itself and in itself (in the gut) more than 30 million of various microorganisms, many of which are quite, quite sickening.
   'They spread the instigators of the deadly sleeping sickness (for people) and nagana (for livestock). No other fly was studied so well as this one... There are about 30 species, and each has its own established demands to the environment. Some need high, other - moderate humidity of air and temperature. Some live in the scrubland, others - in the gallery woods that grow along the river banks, the third - in the tropical rain forests. The choice of victims is different too: some bite people, others don't. Some drink the blood of large ungulates and livestock, others - of small mammals, birds, crocodiles and monitor lizards' (Peter Richel).
   The talk is about the glossine flies. The famous tsetse fly belongs to it. It specifically spreads the sleeping sickness. It's a viviparous fly! It bears its larvae a week or two. They are born already ready to pupate. By that time the fly hides somewhere, in a shadowy place. The larvae bury themselves and soon pupate. The tsetse fly gives birth 8-10 times during it life.
   Horseflies are big flies (up to 2-3 cm). The pain of their bites and their overall annoyance during a hot summer day is known to everyone through personal experience. Domestic livestock, wild animals - moose, deer, even rodents, birds and large lizards - they all suffer from the bites of horseflies. Only females suck blood (and each time each one sucks as much as 70 mosquitoes!). The horsefly males drink the flower nectar, sweet tree sap, "honeydew" that is produced in plenty by the aphids.
   After several days a blood-sated female lays eggs. Later it attacks the wretched animals once more, then there's the next egg-laying - and so up to five times.
   Usually the horseflies adhere their eggs to plants that grow next to water and above it. The larvae live in water or in damp places on land. They have no legs; they're replaced by thickenings and bumps on the body. By pushing around with them, the larvae crawl quite quickly. They're carnivores. They attack larvae of other insects, crustaceans, earthworms.
   Botflies are smaller than the horseflies, but are even more unpleasant insects than they. These are dangerous parasites. Their larvae parasitize various animals. There are subcutaneous botflies, stomach-dwelling, nasal-dwelling...
   In Central and South Americas lives a green and yellow-legged fly, the dermatobia botfly. The natives call its larvae the mosquito worms. These flies fly where plenty of mosquitoes are. How they are able to do the following: to approach the mosquito in mid-flight and by just touching its abdomen to the mosquito, stick their eggs to it?
   In six days the larvae will hatch, but they will stay within the egg shells until the time when the mosquito, in order to drink blood, will land on some warm-blooded animal. As soon as that happens, the botfly larvae immediately move onto the skin of that mammal (or human). They gnaw a hole in it and grow, forming a very painful boil up to 2 or more cm. in diameter. The boil has a hole that which the larva gets the air it breathes. The same hole serves as the exit to the matured larva through which it emerges and falls to the ground, where it pupates, transforming into the mature botfly, which, if it's a female, immediately goes in search of males of its own species, and then of mosquitoes.
   The female of the stomach-dwelling hook botfly lays its eggs onto the skin of asses and horses exactly on the places where these perissodactyls scratch with their teeth most often, for example onto the internal sides of the forelegs. Ending up in the mouth of a horse the botfly larvae live and develop for about a month in the tissues of its tongue. Then they penetrate the moist inner surface of the mouth via which they reach the throat and stomach, where dozens and hundreds of larvae live all at once. When they're ready to pupate they leave with the dung and complete the metamorphosis on the ground.
   Another botfly that parasitizes on the perissodactyls lays its eggs on the horses" lips. Its larvae develop not in the stomach, but in the thin intestine. And the grassy botfly adheres its eggs not to the hide, but to the grass. The horses eat them with the grass.
   The nasal-dwelling botflies are viviparous. Their females literally shoot the larvae into the nostrils of horses, deer, fallow deer, moose, roe deer, and sheep. But that doesn't mean all of the larvae that hatched from the eggs while still in their mother's body (they can number up to five hundred), get into the animal's nostrils with the help of their dipterous mother, but only a small number. If there'll be too many, they'll kill their animal host and die themselves. From the nostrils the larvae move to the mouth, they develop there, and then they emerge back through the nostrils. In sheep they move into frontal lobes and if there'll be several dozen of botfly larvae, the sheep catches "the false whirligig": it starts to move around and around and quickly perishes.
   The sheep and horse subcutaneous botflies shoot their larvae into the eyes as well, and not only of mammals, but of humans. Then the eye gets inflamed and people catch conjunctivitis.
   The larvae of subcutaneous botflies that penetrate head and eyes cause a more dangerous disease among people. An operation is necessary to extract them from there.
   The larvae of subcutaneous botflies parasitize domestic and wild animals, usually ungulates, but the rodents as well. The females of these botflies lay their eggs onto the fur. The larvae penetrate the skin; hide beneath it, then via the subcutaneous tissues or muscles they move upwards, to the back of their animal host. This journey takes several months. A big boil with a hole forms under the skin there, through which the larva emerges and falls to the ground, where it pupates.
   The botflies adaptations to a parasitic life are amazing. But the reaction of the animals, approached by the botflies to lay their eggs is no less surprising. After all, it happens completely painlessly, unlike the botfly bites. Yet the deer, roe deer, cows, horses immediately come to attention, and quickly flee at the approach of a botfly. How do they recognize the botfly in the approaching insect and how do they learn that a contact with it can result in a painful disease? The scientists who study animal behaviour have food for thought here.
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