Head lice very quickly multiply. The entire life cycle of the head lice from the first egg to the egg laid by the already adult female, under favorable conditions, is only 16 days. And with the most unfavorable conditions, but still permitting the reproduction of these parasites, about 30 days.
This means that after a month and a half after infection, a whole population of insects will live on the person's head, and after three months they will begin to pester the owner so much that they will cause pronounced manifestations of pediculosis.
However, despite the short life expectancy, the way lice reproduce attracts the close attention of scientists. For their fleeting life cycle, lice undergo several stages of development, each of which has many features and deserves a separate examination.
The high rate of reproduction of lice only adds variety and an abundance of interesting details in this process.
It is interesting
Reproduction of lice proceeds almost identically in different species and forms of the same species. For example, the number and duration of each stage of development of lice and the duration of the development cycle of the head, clothing and pubic lice are almost identical, differing only in some smallest details. Therefore, further describing how lice on their heads multiply, we will only make small notes about the features of this process in other species.
The head louse is one of two forms of lice common only in man. The second form - the product of exclusively human civilization - is a louse, adapted to life on clothes and nourishment on the skin of a person dressing in contaminated things.
But the pubic louse is a completely different species, although due to similar conditions of existence, the life cycle of lice pubes is almost identical to that of the head lice.
Lice life cycle
Lice belong to insects with incomplete transformation. This means that the life cycle of development of head lice does not include the stage of a typical larva, which in other insects is usually very different in appearance and mode of feeding from adults.
The adult female mates during the first day or two after the last larval moult, and after a few hours begins to lay eggs. Since the source of feed (man) is always "with lice," they do not have developmental delays due to hunger strikes in other parasites.
It is interesting
Lice in principle do not know how to starve. Each insect must be fed every few hours, and if there is no food for two or three days, the louse perishes. The pubic louse can fast for a maximum of 10 hours.
Egg lice are attached to hairs at different distances from the root of the hair. Each egg is dressed in a sticky case, due to which it sticks to the hair quite tightly. Such a design of an egg and a case is called a nit. With an unaided eye, it resembles a simple white dash on a thread, while examining under a microscope - a neat handbag tightly wrapping the hair.
From the nits, the larva of the first age hatchs rather quickly. It is very similar to an adult insect, but it has very small dimensions and an underdeveloped reproductive system. After the first saturation, such a tiny larva immediately molts and turns into a nymph.
It is interesting
A nymph in zoology is called an insect larva, little different from adult individuals (imago). For example, nymphs have cockroaches and grasshoppers. But in butterflies and beetles in the development cycle there is a real larva, absolutely not like an imago.
A rapid cycle of development of lice suggests the presence of only three lines and, correspondingly, three ages of nymphs. Moults are required for nymphs because the chitinous cover of their body is not elastic and can not grow together with the soft tissues of an insect. Accordingly, when such a "suit" becomes small, the nymph changes it.
After the third molt, the nymph becomes an adult insect. The female lice each day lays 2-4 eggs - up to 140 for the whole life.
It is interesting
The head and head lice differ considerably from each other in the details of the structure of the legs and certain features of the shape of the body. If placed in a limited amount of lice of different forms, they can even breed (interbreed), and after a few generations the differences between them will disappear.
Reproduction of lice on the head: a process under a microscope
Reproduction of lice in man is full of interesting details. For example, the process of hatching a larva from an egg is entertaining - the insect pierces its jaws with a lid of nits, but can not get out on its own. But at this time the larva actively breathes, passing the air through its digestive system and pushing it through the anus. The air that accumulates in the bottom of the nit pushes the larva out of the boot, and it falls on the scalp, where it immediately begins to feed.
Different stages of development of lice are characterized by different periods of existence:
- 5-8 days develops nits
- 1-3 days requires a larva to become a nymph of the first age
- 5 days develops a nymph of the first age
- 8 days a nymph of the second age develops.
The adult louse lives from 30 to 42 days, and the registered longevity record for these insects was 46 days. Narrowly delineated in terms of life expectancy and reproduction period in lice are due to the stability of the conditions in which head lice dwell at all stages of their development.
Female lice mate with males already in the first hours after leaving the nymph. One copulation is enough for them to fertilize all the eggs in the body. Then every day the female lays several eggs. Head lice have about 2-4 eggs a day, pubic lice have 1-3 eggs, and in the case of a lamb - up to 10 eggs.
Accordingly, for his life:
- the female head louse lays up to 140 eggs (usually about 80)
- the female pubic louse leaves about 50 eggs
- The female louse lays up to 300 eggs.
The egg itself in the sexual glands of the female is smeared in a sticky secret, part of which is removed from the oviduct before the egg. This secret also forms a shell of nits, due to which it is attached to the hair.
After the egg is laid, the secret hardens and ensures a secure attachment of the egg.
The video below clearly demonstrates how the lice multiply.
In the overwhelming majority of cases, the life cycle of a louse passes on the surface of the head of the same person. However, in case of close contact of people with each other or when combing, the insect can get on the head of another person and give a start to a new population here. This is the transmission of pediculosis.
The conditions under which lice reproduce
Reproduction of head lice occurs in rather limited temperature intervals. Their nits cease to develop at temperatures below 22 ° C and above 45 ° C. The optimum temperature for a quick course of the life cycle of the head lice is 30-31 ° C.
Head lice reproduce as quickly as possible with a large number of them on their heads, when females and males do not have to search for each other for a long time. These parasites are species-specific, that is, they can not infect another host, except humans and some very closely related species of monkeys.
It is believed that the lice reproduce at the highest speed in places where many people live together. They were a huge disaster in the days of wars and people living in barracks.
Features of reproduction of different types of lice
The cycle of head lice development is almost identical to that of pubic and lice. Differences here are only in fertility (the louse is much more prolific and therefore multiplies faster, the pubic louse lays less eggs) and the ability of the louse to multiply in different parts of the body. For example, the pubic louse can parasitize on the head in children, but the head even does not pass over to the beard of men.
Features of reproduction head lice does not affect the ways to combat it. Like other parasites, the louse is etched with insecticide-containing shampoos, and with a regular shave of the head, insects are lost by themselves, unable to lay eggs and wash off with water procedures.
Getting rid of lice and nits at home for 1 procedure: