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Charles Darwin wrote in 1881 that archaeologists should be grateful for the preservation of many ancient objects to earthworms, under the excrement of which coins, jewelry, and stone tools were safely stored for many centuries. In addition, the great naturalist found that in a few years the worms pass the entire arable layer of soil through their body, and their countless minks form a kind of capillary network of the earth, providing its ventilation and drainage.
There are a huge number of earthworms (earth) on Earth: about 6000 species. They live on all continents except Antarctica.
Especially a lot of them in the tropics. adult earthworm can reach a length of 15 cm, in the tropics there are 3 meter individuals.
Lumbricus terrestis spends its entire life in the ground, tirelessly digging passages. They usually appear on the surface during rains due to lack of oxygen and at night.
The body of the worm consists of several tens or even hundreds of segments (80-300). When moving, it relies on bristles, which are present on all segments except the first. They are characterized by a closed circulatory system. Red blood. One vein and one artery run through the entire body. Breathing is carried out by the entire surface of the body, covered with mucus. The nervous system is represented by two nerve nodes (the brain) and the abdominal chain. Capable of regeneration. Earthworms are hermaphrodites, that is, each sexually mature individual has a male and female reproductive system. Cross fertilization is common.
A photo: internal structure digestive system of earthworms.
Reproduction of earthworms.
Video: The principle of dropping a cocoon in an earthworm.
The structure of the earthworm: digestive, nervous and circulatory systems.
Video: Earthworm movement
The mink of an earthworm is a long channel, which on a hot summer day descends to a depth of 1.5 meters. Feeds on soil, fallen leaves and debris herbaceous plants. Penetrating the soil with their numerous passages, they loosen it, mix it, moisten it and fertilize it. During the day, the earthworm passes through itself organic substances in an amount equal to its body weight. If the earth is loose, then Lumbricus terrestis tears off a piece of earth with its lips and swallows it; if it is dry, it wets it with saliva.
The body of the earthworm is divided into segments by ring constrictions. Each segment has eight small bristles, which, when the worm moves, rest against the unevenness of the soil.
The body wall is covered with a cuticle secreted by a single-layer epithelium. Below it is a layer of circular muscles, below them are longitudinal muscles. Thanks to the alternating work of these muscles, the worm moves. The movement is facilitated by secreted mucus.
Earthworm refers to annelids with a secondary body cavity - in general. Its walls are lined with epithelium. The cavity is filled with a fluid capable of carrying nutrients and oxygen absorbed by the entire surface of the body. Respiratory system missing. (During the rain, the worms lack oxygen and crawl out to the surface of the soil).
The mouth is located on the ventral side of the anterior segment, and the anus is located on the latter. The worm feeds on fallen leaves and rotting plant remains swallowing them along with the earth. Nutrients in the intestines are absorbed into the blood. Undigested residues are ejected through the anus.
Circulatory system closed. The dorsal vessel carries blood from the posterior to the anterior end of the body. Several annular vessels in segments 7–11 play the role of the heart, pumping blood into the abdominal vessel. Through the abdominal vessel, blood moves to the posterior end. Thinner vessels depart from the main vessels, passing into the capillaries. Blood contains hemoglobin, which carries oxygen. A closed circulatory system allows you to significantly increase the metabolic rate.
In each segment, except for the terminal ones, there is a pair of metanephridia - tubules that bring metabolic products out of the coelom (excretory system).
The nervous system consists of the peripharyngeal nerve ring and the ventral nerve cord. The sense organs are absent. The worm is able to perceive light and touch due to tactile and light-sensitive cells scattered over the entire surface of the body.
Earthworms are hermaphrodites, but with cross fertilization. Segments 32–37 have a belt that serves to build egg cocoons. The cocoon moves to the front end, spermatozoa, obtained in advance by mating with another individual, enter it from the spermatozoa, fertilization occurs. The cocoon slips through the head end of the worm. Development is direct, young worms hatch from eggs. Earthworms are characterized by the ability to regenerate - to restore the lost fragment of the body.
The value of the earthworm in nature
- Earthworms make passages in the soil, facilitating the penetration of air and water into the soil.
- Improve soil structure by gluing soil particles into small lumps.
- Soil fertility is facilitated by the worms dragging fallen leaves and other plant residues into the burrows, their digestion and decomposition with the formation of humus.
- Earthworms serve as food for many animals: moles, shrews, hedgehogs, toads, ground beetles.
- They are intermediate hosts of helminths that cause diseases in young pigs, etc.
Animals, suborder earthworms. The body of an earthworm consists of annular segments, the number of segments can reach up to 320. When moving, earthworms rely on short bristles that are located on the body segments. When studying the structure of an earthworm, it is clear that, unlike the whipworm, its body looks like a long tube. Earthworms are distributed throughout the planet, except for Antarctica.
Appearance
Adult earthworms are 15 - 30 cm in length. In the south of Ukraine, it can reach large sizes. The body of the worm is smooth, slippery, has a cylindrical shape and consists of piece rings - segments. This form of the body of the worm is explained by the way of its life, it facilitates movement in the soil. The number of segments can reach 200. The ventral side of the body is flat, the dorsal side is convex and darker than the ventral side. Approximately where the front of the body ends, the worm has a thickening called a girdle. It contains special glands that secrete a sticky liquid. During reproduction, an egg cocoon is formed from it, inside which the eggs of the worm develop.
Lifestyle
If you go out into the garden after rain, you can usually see small piles of earth thrown out by earthworms on the path. Often at the same time, the worms themselves crawl along the path. It is because they appear on the surface of the earth after rain that they are called rain. These worms crawl out to the surface of the earth also at night. The earthworm usually lives in humus-rich soil and is not common in sandy soils. He also does not live in swamps. Such features of its distribution are explained by the way of breathing. The earthworm breathes on the entire surface of the body, which is covered with mucous, moist skin. Too little air is dissolved in the water, and therefore the earthworm suffocates there. He dies even faster in dry soil: his skin dries up, and breathing stops. In warm and humid weather, earthworms stay closer to the surface of the earth. During a prolonged drought, as well as during a cold period, they crawl deep into the ground.
moving
The earthworm moves by crawling. At the same time, it first draws in the anterior end of the body and clings with the bristles located on the ventral side to the unevenness of the soil, and then, contracting the muscles, pulls up the posterior end of the body. Moving underground, the worm makes its own passages in the soil. At the same time, he pushes the earth apart with the pointed end of the body and squeezes between its particles.
Moving in dense soil, the worm swallows the earth and passes it through the intestines. The worm usually swallows the earth at a considerable depth, and throws it out through the anus at its mink. So on the surface of the earth long "laces" of earth and lumps are formed, which can be seen in the summer on garden paths.
This method of movement is possible only in the presence of well-developed muscles. Compared to the hydra, the earthworm has more complex musculature. She lies under his skin. Muscles together with the skin form a continuous musculocutaneous sac.
The muscles of the earthworm are arranged in two layers. Beneath the skin lies a layer of circular muscles, and beneath them is a thicker layer of longitudinal muscles. Muscles are made up of long contractile fibers. With the contraction of the longitudinal muscles, the body of the worm becomes shorter and thicker. When the circular muscles contract, on the contrary, the body becomes thinner and longer. Contracting alternately, both layers of muscles cause the movement of the worm. Muscle contraction occurs under the influence of the nervous system, branching out in muscle tissue. The movement of the worm is greatly facilitated by the fact that there are small bristles on its body from the ventral side. They can be felt by running a finger dipped in water along the sides and along the ventral side of the worm's body, from the rear end to the front. With the help of these bristles, the earthworm moves underground. With them, he lingers when he is pulled out of the ground. With the help of bristles, the worm descends and rises along its earthen passages.
Food
Earthworms feed mainly on half-decayed plant remains. They drag, usually at night, leaves, stems and other things into their minks. Earthworms also feed on humus-rich soil, passing it through their intestines.
Circulatory system
The earthworm has a circulatory system that the hydra does not have. This system consists of two longitudinal vessels - dorsal and abdominal - and branches that connect these vessels and carry blood. The muscular walls of the vessels, contracting, drive blood throughout the body of the worm.
The blood of an earthworm is red, it has a very importance. With the help of blood, the connection between the organs of the animal is established, metabolism occurs. Moving through the body, it carries nutrients from the digestive organs, as well as oxygen entering through the skin. At the same time, the blood carries carbon dioxide out of the tissues into the skin. Various unnecessary and harmful substances formed in all parts of the body, together with the blood, enter the excretory organs.
Irritation
The earthworm does not have special sense organs. He perceives external stimuli with the help of the nervous system. The earthworm has the most developed sense of touch. Sensitive tactile nerve cells are located all over the surface of his body. The sensitivity of the earthworm to various kinds of external irritation is quite high. The slightest vibrations of the soil make him quickly hide, crawling into a mink or into deeper layers of soil.
The value of sensitive skin cells is not limited to touch. It is known that earthworms, having no special organs of vision, still perceive light stimuli. If at night you suddenly illuminate the worm with a lantern, it quickly hides.
The response of an animal to stimulation, carried out with the help of the nervous system, is called a reflex. There are different types of reflexes. The contraction of the body of the worm from touch, its movement when suddenly illuminated by a lantern, has a protective value. This is a protective reflex. Grabbing food is a digestive reflex.
Experiments also show that earthworms smell. The sense of smell helps the worm find food. Charles Darwin also established that earthworms can smell the leaves of the plants they feed on.
reproduction
Unlike the hydra, the earthworm reproduces exclusively sexually. It does not have asexual reproduction. Each earthworm has male organs - the testes, in which the gums develop, and the female genital organs - the ovaries, in which the eggs are formed. The worm lays its eggs in a slimy cocoon. It is formed from a substance secreted by the girdle of the worm. In the form of a clutch, the cocoon slides off the worm and is pulled together at the ends. In this form, the cocoon remains in the earthen burrow until young worms emerge from it. The cocoon protects the eggs from moisture and other adverse effects. Each egg in the cocoon divides many times, as a result of which tissues and organs of the animal are gradually formed, and, finally, small worms similar to adults emerge from the cocoons.
Regeneration
Like hydras, earthworms are capable of regeneration, in which lost parts of the body are restored.
The rain church has an elongated, 10-16 cm long body. In cross section, the body is rounded, but, unlike roundworms, it is divided into 100-180 segments by annular constrictions. Each segment has small elastic setae. They are almost invisible, but if you run your fingers from the back end of the worm's body to the front, then we will immediately feel them. With these bristles, the worm clings to the unevenness of the soil when moving.
Figure: earthworm and the movement of the worm in the soil
Earthworm habitat
During the day, the worms stay in the soil, making passages in it. If the soil is soft, then the worm bores it with the front end of the body. In doing so, he first compresses the front end of the body, so that it becomes thin, and pushes it forward between the lumps of soil. Then the front end thickens, pushing the soil apart, and the worm pulls up the back of the body. In dense soil, the worm can eat its own way, passing the earth through the intestines. Heaps of earth can be seen on the surface of the soil - they are left here by worms at night. They also come to the surface after heavy rain(hence the name - rain). In summer, the worms stay in the surface layers of the soil, and for the winter they dig minks up to 2 m deep.
Skin-muscular sac
If we take the worm in our hands, we will find that its skin is moist, covered with mucus. This mucus facilitates the movement of the worm in the soil. In addition, only through wet skin there is a penetration into the body of the worm of oxygen necessary for respiration.
Under the skin are located circular muscles fused with it, and under them a layer of longitudinal muscles - a skin-muscular sac is obtained. The circular muscles make the body of the worm thin and long, while the longitudinal muscles shorten and thicken. Thanks to the alternating work of these muscles, the movement of the worm occurs.
The body cavity of an earthworm
Figure: the internal structure of the earthworm
Under the skin-muscle sac is a fluid-filled body cavity in which the internal organs are located. This body cavity is not continuous, as in roundworms, but is divided by transverse septa according to the number of segments. It has its own walls and is located under the skin-muscle sac.
Earthworm digestive organs
Picture: digestive system earthworm
The mouth is located at the anterior end of the body. The earthworm feeds on decaying plant debris, which it swallows along with the earth. It can also drag fallen leaves from the surface. Swallowing is done with a muscular pharynx. The food then enters the intestines. Undigested residues, together with the earth, are ejected through the anus at the posterior end of the body.
Figure: earthworm circulatory system
The circulatory system of the earthworm serves to carry oxygen and nutrients primarily to the muscles. An earthworm has two main blood vessels: dorsal blood vessel through which blood moves from back to front, and abdominal blood vessel through which blood flows from front to back. Both vessels in each segment are connected to annular vessels. Several thick annular vessels have muscular walls, due to the contraction of which blood moves. Thinner ones depart from the main vessels, then branching into the smallest capillaries. Oxygen from the skin and nutrients from the intestines enter these capillaries, and these substances are released from other similar capillaries branching in the muscles. Thus, the blood moves all the time through the vessels and does not mix with the cavity fluid. Such a circulatory system is called a closed circulatory system.
Excretory system of the earthworm
Liquid waste, processed substances enter the body cavity. Each segment contains a pair of tubules. Each tube has a funnel at the inner end, processed unnecessary substances enter it and are removed through the tube through the opposite end to the outside.
Picture: nervous system earthworm
A pair of nerve trunks runs along the entire body of the worm along the ventral side. In each segment they have developed nerve knots- it turns out nerve chain. In the front part, two large nodes are connected to each other by ring bridges - a parapharyngeal nerve ring. From all nodes, nerves depart to various organs.
Sense organs of the earthworm
There are no special sense organs, but sensitive cells in the skin allow the earthworm to feel touch on its skin and distinguish light from darkness.
Reproductive system and reproduction of the earthworm
Earthworms are hermaphrodites. Before laying eggs, two worms touch for a while and exchange seminal fluid - sperm. Then they diverge, and mucus is released from the thickening (girdle) on the front of the worm. Eggs enter this mucus. Then a lump of mucus with eggs slides off the body of the worm and freezes in cocoon. Young worms emerge from the cocoon.
Many people underestimate the importance of the work of earthworms. These representatives of the invertebrate kingdom are best known for crawling out of the ground in large numbers after heavy rain. They are often used as bait by numerous fishing enthusiasts. Darwin also noted the fact that worms perform an important function in nature, acting as a kind of agricultural technicians. In the process of creating an extensive system of tunnels that the earthworm breaks through, excellent aeration is formed through the flow of air to the inner layers of the soil.
Thanks to excellent aeration, the respiratory activity of many plants is facilitated. Feeding on organic matter and waste, worms ensure the grinding of soil components, while enriching them with their secretions. The amazing ability of representatives of this species is the ability to disinfect huge areas of soil, sterilizing it from harmful bacteria. Thanks to countless burrows that form a semblance of a capillary system, perfect drainage and ventilation of the soil is ensured.
The body of an earthworm can reach three meters in length. However, on the territory of Russia, there are mainly individuals whose body length does not exceed 30 centimeters. In order to move, the worm uses small bristles that are located on different parts torso. Depending on the variety, there can be from 100 to 300 segments. The circulatory system is closed and very well developed. It consists of one artery and one central vein.
The structure of the earthworm is very unusual. Breathing is realized with the help of special supersensitive cells. The skin produces a protective mucus with a sufficient amount of natural antiseptics. The structure of the brain is quite primitive and includes only two nerve nodes. According to the results of laboratory experiments, earthworms have confirmed their outstanding ability to regenerate. A severed tail grows back after a short period of time.
The genital organs of the earthworm are also arranged in a very unusual way. Each individual is a hermaphrodite. She also has male organs. According to biological factors, all such worms can be divided into several subgroups. Representatives of one of them are looking for food on the surface of the soil layer. Others use the soil itself as food and are extremely rarely shown from the ground.
The earthworm belongs to the type of annelids. Under the skin layer is a developed system of muscles, consisting of muscles various shapes. The mouth opening, from which food enters the esophagus through the pharynx, is located on the front of the body. From there it is transported to the area of the enlarged goiter and the small size of the muscular stomach.
Burrowing and litter earthworms live in places with loose and moist soil. Preference is given to wet soils of the subtropics, swampy lands and the banks of various reservoirs. In the steppe territories, soil varieties of worms are usually found. Litter species live in the taiga and forest-tundra. The coniferous broad-leaved strip can boast of the highest concentration of individuals.
What kind of soil do worms like?
Why do earthworms love sandy and loamy soils? Such soil is characterized by low acidity, which is the most in the best way suitable for their life. The level of acidity above pH 5.5 is detrimental to the organisms of these representatives of the annular type. Moist soils are one of the prerequisites for population expansion. During dry and hot weather, worms go deep underground and lose the ability to reproduce.
The nature and lifestyle of the earthworm
The active and productive life of the earthworm falls on the dark time of the day. As soon as night falls, many individuals crawl out to the surface of the ground in search of food. However, the tail usually remains in the ground. By morning, they return to their burrows with prey, dragging pieces of food into them and masking the entrance to their shelter with blades of grass and foliage.
The role of earthworms in nature is difficult to overestimate. Worm in literally passes through itself an incredible amount of soil mixture, enriching it with beneficial enzymes and killing harmful substances and bacteria. The worm moves by crawling. Pulling in one end of the body and clinging with bristles to the roughness of the earth, it pulls up the rear part, making its many passages in this way.
How do earthworms survive winter?
On the winter period the vast majority of individuals hibernate. A sharp drop in temperature can instantly destroy the worms, so they try to burrow into the soil in advance to a depth often exceeding one meter. Earthworms in the soil perform the most important function of its natural renewal and enrichment with various substances and microelements.
Benefit
In the process of digestion of semi-fermented leaves, the body of the worms produces specific enzymes that contribute to the active generation of humic acid. The soil that has been loosened by earthworms is optimal for a wide variety of representatives of the plant kingdom. Thanks to the system of intricate tunnels, excellent aeration and ventilation of the roots is provided. Thus, the movement of the earthworm is an important factor in the task of restoring the useful qualities of the soil.
The earthworm is in fact very useful for humans. It makes the soil layers fertile and enriches them with all sorts of nutrients. However, the total number of individuals in many regions of Russia is rapidly declining. This happens due to the uncontrolled introduction of pesticides, fertilizers and mineral mixtures into the soil. Numerous birds, moles, and various rodents also prey on earthworms.
What do earthworms eat?
At night, the earthworm crawls to the surface and pulls the half-decayed remains of plants and leaves into its shelter. Also, his diet includes soil rich in humus. One representative of the species can process up to half a gram of soil per day. Considering that up to several million individuals can be located simultaneously on an area of one hectare, they are able to act as indispensable soil converters.
After the rain, a large number of worms can be seen on the asphalt and soil surface, what makes them crawl out? Even the name "earthworms" indicates that they are very fond of moisture and become more active after rain. Consider a few possible causes why do earthworms crawl out after rain to the surface of the earth.
soil temperature
It is believed that the worms crawl to the surface in search of warmth, since after rain the soil temperature drops by several degrees, which causes discomfort for them.
Change in acid-base balance
Another theory says that the worms come to the surface due to a change in the acid-base balance of the soil after rain, it becomes more acidic, which negatively affects these diggers. According to the researchers, emergency evacuation to the soil surface saves them from death in an acidic environment.
Lack of air
The third theory explains that after rain, there is more oxygen in the upper layer of the soil, so the worms crawl out en masse. Water enriches the upper layers of the earth with oxygen, and many types of worms love moisture and vitally need enough oxygen. And through the surface of the body, oxygen is absorbed best in a humid environment.
Travels
British scientist Chris Lowe suggested that worms come to the surface of the earth during rain in order to make an extended journey to new territory. On the surface, worms can crawl much further than underground, and dry soil causes discomfort when moving, strong friction is created, grains of sand stick to the surface of the worm's body, injuring it. And after the rain, the surface of the earth is highly moistened, which allows them to freely travel to new areas of soil.
Sounds of the rain
Another scientist, Professor Joseph Gorris from the USA, suggested that earthworms they are frightened by the sound of rain, since the vibration that it creates is similar to the sound of the approach of their main enemy - the mole. That is why some fishermen use a technique to lure the bait to the surface: they insert a stick into the ground, fix a sheet of iron on its surface and pull it so as to create vibration, while the short is transmitted to the ground through the stick. Frightened, the worms get to the surface of the earth and become easy prey for experienced fishermen.
Reproduction and lifespan of earthworms
The earthworm is a hermaphrodite. It has both female and male reproductive organs. However, he is not capable of self-fertilization. With the onset of warm temperatures required for reproduction climatic conditions individuals crawl in pairs, attaching to each other with the abdominal region, and produce a kind of seed exchange. After that, the clutch is transformed into a cocoon, in which the eggs develop.
Some species differ in asexual reproduction. The body of the worm is divided in two, with one of the parts regenerating the anterior end, and the other regenerating the posterior end. There are also species of worms that reproduce without seed receptacles by laying spermatophores. The lifespan of worms can exceed ten years.
