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In this essay we will discuss about Earthworm. After reading this essay you will learn about: 1. Habitat and Habits of Earthworm 2. Morphology of Earthworm 3. Anatomy 4. Digestive System 5. Digestive Glands 6. Blood Vascular System 7. Hearts and Anterior Loops 8. Excretory System 9. Nervous System 10. Receptors or Sense Organs 11. Reproductive System 12. Copulation and Cocoon Formation and Other Details.
Essay Contents:
- Essay on the Habitat and Habits of Earthworm
- Essay on the Morphology of Earthworm
- Essay on the Anatomy of Earthworm
- Essay on the Digestive System of Earthworm
- Essay on the Digestive Glands of Earthworm
- Essay on the Blood Vascular System of Earthworm
- Essay on the Hearts and Anterior Loops of Earthworm
- Essay on the Excretory System of Earthworm
- Essay on the Nervous System of Earthworm
- Essay on the Receptors or Sense Organs of Earthworm
- Essay on the Reproductive System of Earthworm
- Essay on the Copulation and Cocoon Formation of Earthworm
- Essay on the Interaction of Earthworm with Mankind
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Essay # 1. Habitat and Habits of Earthworm:
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Earthworms are found in wet soil containing rich organic matter. During rainy season, they come out and can be seen easily in lawns, fields and gardens. Life of certain species of earthworm is 4 to 8 years. These nocturnal worms have the following habits.
Earthworms are detrivorous. The food is digested in the gut and undigested food matter along with the soil is passed out through the anus in the form of little heaps of pellets, known as “worm castings”. Earthworms live in burrows secreted by the cutaneous glands.
The animals which live in burrows are called fossorial animals. When the burrows are filled with water, the earthworms come out of their burrows in large numbers and start moving on the soil.
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The earthworm does not have specialized locomotory organs. The locomotion is brought about by the circular and longitudinal muscles of the body wall, aided by the chitinous curved setae embedded in the skin. Earthworms move at the rate of about 15 cm per minute.
The special respiratory organs are lacking in earthworms. The gaseous exchange takes place by the body wall (cutaneous respiration). The surface of the body wall is kept moist by the secretion of epidermis cells and coelomic fluid, which oozes out of the body through dorsal pores.
The body wall is thin and richly supplied with blood. The blood carries an oxygen carrier protein, the hemoglobin dissolved in the plasma. The atmospheric oxygen diffuses into the blood, where it combines with hemoglobin to form oxyhaemoglobin.
The earthworm breeds in rainy season. It is hermaphrodite or bisexual or monoecious, viz. both male and female sex organs are found in one individual. Earthworms are protandrous, viz. male sex organs mature earlier than the female.
Hence, cross fertilization occurs. This involves copulation of two worms and mutual exchange of spermatozoa (sperms). The animal is oviparous. Several eggs and spermatozoa are packed in the cocoon and on an average four baby worms develop in one cocoon.
Earthworms possess a great power of regeneration. It is observed that if a worm is cut into two parts accidentally, the anterior half will develop the posterior half, the anterior part can be formed only if 4 to 6 anterior segments are removed. Grafting is also possible in the earthworms. A cut part of an earthworm can be grafted to another worm.
Essay # 2. Morphology of Earthworm:
The mature P. posthuma is about 150 mm. in length and 3 to 5 mm. in width. The colour is glistening dark brown due to the pigment porphyrin. The dorsal surface is darker than ventral.
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Segmentation:
The body comprises 100 to 120 segments or metameres which are distinct externally by the circular burrows, the annuli. The latter correspond internally as septa to divide the body cavity into compartments. This type of segmentation which is both external and internal is known as true or metameric segmentation or metamerism.
The first segment of the body is termed as peristomium (buccal segment) which bears a sensory fleshy lobe, the prostomium, anteriorly. The peristomium contains a crescentic mouth, overhung by the prostomium. The clitellum (= cingulum), a prominent circular band of glandular nature, is found from the 14th to 16th segments. These segments are not distinct externally.
The clitellum secretes mucus and albumen. Its secretion helps in the formation of cocoon, which is used for fertilization of the eggs. On the basis of the clitellum, the body of earthworm is divisible into preclitellar, clitellar and post-clitellar regions.
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Setae:
Except the first, the last and clitellar segments each segment bears a ring of tiny curved, chitinous structures known as setae or chaetae. They are embedded in the skin. Each seta (singular of setae) lies in a setal sac, which is a small pit in the skin. The sac has special muscles to move the seta out or in and to bend it forward or backward.
The seta is somewhat ‘S’ shaped having a swollen middle portion, the nodulus. The part of seta in the setal sac is called the base and that projecting out is termed the neck. The setae are renewed if lost. The setae hold the substratum firmly. Thus, they help in the locomotion. They also keep the two copulating worms together by penetration into each other’s body.
Pores and Apertures:
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(i) Mouth:
The peristomium encloses a crescentic shaped mouth on its anterior end. It is overhung by the fleshy prostomium.
(ii) Anus:
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It is a situated in the last or anal segment or pygidium.
(iii) Female Genital Pore:
It is a situated on the ventral side of the 14th segment. The ova are passed out by this pore.
(iv) Male Genital Pores:
These are a pair of crescentic openings, lying on the ventral side of the 18th segment. Male reproductive fluid containing sperms is discharged by these pores.
(v) Apertures of Accessory Glands:
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There are present two pairs of genital papillae on the ventral side of the 17th and 19th segments, one pair in each segment. Each papilla has fine apertures of accessory glands.
(vi) Spermathecal Apertures:
These are four pairs of small openings situated ventrolaterally in the inter-segmental grooves of the segments 5/6, 6/7, 7/8 and 8/9 on each side. Each opening leads into a sperm theca, in which the sperms of the other earthworm are stored.
(vii) Nephridiopores:
These are numerous, minute openings, scattered irregularly all over the body surface, except the first two segments. The nephridiopores are the openings of the integumentary nephridia to expel out the nitrogenous wastes from the body.
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(viii) Dorsal pores:
These are minute openings, lying on the mid-dorsal line in the inter-segmental grooves, behind the 12th segment. The first dorsal pore is situated in between 12th and 13th grooves. The body cavity or coelom opens outside by these pores to discharge its coelomic fluid. The fluid keeps the body surface smooth and moist, and also protects the animal from the harmful bacteria.
Essay # 3. Anatomy of Earthworm:
Body wall:
It consists of the cuticle, epidermis, muscular layer and the parietal peritoneum.
i. Cuticle:
It is a thin delicate nоn-cellular chitinous membrane secreted by the underlying epidermis.
ii. Epidermis:
It lies beneath the cuticle and is made up of a single layer of columnar epithelial cells. It consists of (i) Supporting cells, (ii) Glandular cells— (a) Mucous or Goblet cells (b) Albumen cells and cocoon forming cells (iii) Basal cells (iv) Receptor cells or sensory cells and (iv) Setal cells (seta forming cells).
iii. Muscular layer:
It consists of an outer layer of circular muscles and an inner layer of longitudinal muscles. A set of circular muscles also lies outer to parietal peritoneum. The longitudinal muscles layer lies in long paralleled bundles.
iv. Parietal layer of Coelomic Peritoneum or Parietal Peritoneum:
It is the innermost layer of the body wall. It forms the outer boundary of coelom and is, therefore, called parietal peritoneum. It secretes coelomic fluid.
Coelom (Body Cavity):
Coelom is the space between the body wall and alimentary canal lined externally by the parietal peritoneum and internally by the visceral peritoneum. It is filled with the coelomic fluid. In earthworm coelom is formed by the splitting of the mesoderm of the embryo, therefore, it is called schizocoelom.
Septa:
The coelom in the earthworm is not a continuous cavity but is divided into compartments by transverse circular partitions, the septa. However, it may be stated here that the coelom of the first four segments is continuous or undivided.
Thus the first septum which is thin and membranous lies between the fourth and fifth segments, the next five septa lying between segments 5/6, 6/7, 7/8, 8/9 or 9/10 and 10/11 are thick and muscular. One of the two septa, either between the 8th and 9th or between the 9th and 10th segments is absent.
Coelomic Fluid:
It is a milkish fluid filling the coelom. It consists of water, proteins, salts, etc. and is slightly alkaline in nature.
It contains four types of corpuscles:
(i) Phagocytes (= Eleocytes):
They move like Amoeba and engulf harmful germs.
(ii) Circular cells:
The function of these cells is not fully understood.
(iii) Chloragogen cells or Yellow cells:
These cells are excretory in function. Mucocytes. These are elongated cells whose one end forms a fan like structure and the other narrow end contains the nucleus. The function of these cells is not known. Coelomic fluid makes the body segments turgid and thus helps in locomotion. It serves as hydro skeleton.
Lymph glands:
These are white fluffy bodies which are found arranged on either side of the dorsal blood vessel from 26th segment and extend to the successive segments. These glands are believed to produce the phagocytes of the coelomic fluid.
Essay # 4. Digestive System of Earthworm:
It consists of alimentary canal (Fig. 7A.7) and digestive glands.
Alimentary canal:
It is a straight tube like structure with variable diameter extending from the mouth to the anus. It consists of the buccal cavity, pharynx, oesophagus, gizzard, stomach and intestine.
i. Mouth:
Mouth is situated in the first segment (peristomium). It is overhung dorsally by sensitive fleshy lobe the prostomium—an extension of the peristomium.
ii. Buccal Cavity:
Mouth leads into a thin walled buccal cavity which extends from first segment to the 3rd segment.
iii. Pharynx:
The buccal cavity is followed by the pharynx which extends up to the fourth segment. On the roof of the pharynx a muscular, glandular and vascular pharyngeal gland or mass is present.
iv. Oesophagus:
The pharynx leads into a narrow and tubular structure, the oesophagus which extends from the fifth segment to the seventh segment.
v. Gizzard:
It is found in the eighth segment or in the eighth and ninth segments. Gizzard grinds the food with the help of thick muscles and cuticle.
vi. Stomach:
It extends from the ninth to the fourteenth segment.
vii. Intestine:
The intestine can be distinguished into three regions:
(i) Pretyphlosolar region:
It extends from 15th to the 26th segment. In 26th segment, the intestine gives off a pair of short outgrowths, the intestinal caecae which extend forwards through 3 or 4 segments. The internal epithelium of the intestinal caecae is glandular. This region is without typhlosole.
(ii) Typhlosolar region:
It is the middle region of the intestine which runs from the 27th segment upto about 23 to 25 segments in-front of the anus. In this region, the mid-dorsal wall of the intestine is thrown into a longitudinal fold which is known as typhlosole. The typhlosole increases the absorptive surface of the intestine.
(iii) Post-typhlosolar region:
It is the posterior region of the intestine which lies in the last 23 to 25 segments. It mainly stores the faecal matter and opens to the exterior through the anus. This region is without typhlosole.
Anus:
It is situated in the anal (last) segment, which opens to the outside to egest the faecal matter.
Essay # 5. Digestive Glands of Earthworm:
(i) Pharyngeal gland or mass:
It is situated at the roof of the pharynx. Its glandular cells are known as chromophil cells which secrete a fluid, the saliva which is passed on to the lumen of the pharynx. Saliva contains mucus (a lubricating agent) and a proteolytic enzyme.
(ii) Gastric epithelium:
The glandular cells of the enteric epithelium of the stomach secrete a gastric fluid which contains proteolytic enzyme.
(iii) Intestinal epithelium:
The glandular cells of the enteric epithelium of the intestine secrete an intestinal fluid which contains proteolytic, amylolytic and lipolytic enzymes.
(iv) Intestinal caecae:
These are the two outgrowths of the intestine arising in the 26th segment and extend forwards up to 3 or 4 segments. They secrete a digestive fluid which contains amylolytic type of enzyme which is transferred to the lumen of the intestine.
Ingestion:
Earthworms mainly feed upon the decaying organic matter found in the soil. They also sometimes feed on the bits of plant and animal matter. Thus earthworms are omnivorous in diet.
Digestion:
In the pharynx, secretion of the pharyngeal gland cells (= chromophil cells) contains mucin and protein-splitting enzyme. The mucin lubricates the soil for easy passage onwards while enzyme splits the protein of food particles into peptones and proteoses. The soil and food particles are carried to the gizzard through the oesophagus.
The soil and food particles are ground up in the gizzard. Glandular cells of stomach epithelium secrete another proteolytic enzyme which splits the remaining proteins of food into peptones and proteoses. Following enzymes are secreted by glandular cells of intestine and intestinal caecae which act in the intestine.
(i) Proteases complete the digestion of proteins by breaking the peptones and proteoses into amino acids,
(ii) Lipase splits fats into fatty acids and glycerol,
(iii) Amylases digest the starch and glycogen,
(iv) Cellulase digests the cellulose of leaves, etc.
(vi) Chitinase digests the chitin of insects. Thus digestion is completed in the intestine.
Absorption:
Absorption of digested nutrients occurs in the intestine, especially in its typhlosolar region. Absorbed nutrients reach the blood capillaries of the intestinal wall and circulate throughout the body.
Egestion:
The undigested food matter along with soil is passed out through anus in the form of little heaps or pellets, called the “worm castings”.
Essay # 6. Blood Vascular System of Earthworm:
Blood vascular system of earthworm is closed type as the blood flows in the closed blood vessels.
Blood:
A coloured respiratory pigment, the haemoglobin, is present in the plasma. Due to the presence of haemoglobin the colour of the plasma is red. Only one type of blood corpuscles, the leucocytes are present in the blood of earthworm. The leucocytes kill the harmful germs which may enter the body of the earthworm.
Blood Vessels:
Following are the prominent blood vessels found in earthworm:
i. Dorsal blood vessel:
It extends from one end of the body to the other. The blood flows in this vessel from behind to forward on the dorsal side of alimentary canal. The dorsal blood vessel has valves which prevent the backward flow of blood.
ii. Ventral blood vessel:
It also extends from the one end to the other end of the body. It does not have any valves and flow of the blood is from the anterior to the posterior end of the body. It is a main distributing blood vessel.
iii. Sub-neural blood vessel:
It runs from the posterior end of the body up to the fourteenth segment in-front. It collects blood from the body wall and the nerve cord. The blood thus collected is sent to the dorsal blood vessel through commissural vessels.
iv. Lateral oesophageal blood vessels:
(According to some authors, the part of alimentary canal from 5th segment up to the 14th segment is called oesophagus). These are paired blood vessels lying one on either ventrolateral side of alimentary canal between the body wall and the alimentary canal in the first fourteen segments. Both the lateral oesophageal vessels are continuation of the sub-neural vessel in the 14th segment.
v. Supra-oesophageal blood vessel:
It is a single vessel which lies on the dorsal side of alimentary canal between the 9th and the 13 segments. It receives blood from the lateral oesophageals through two pairs of anterior loops and pours into two pairs of laterooesoph ageal hearts present in the 12th and the 13th segments.
Essay # 7. Hearts and Anterior Loops of Earthworm:
In earthworm, there are present four pairs of tubular hearts. These hearts are provided with valves. The anterior two pairs of hearts, known as lateral hearts lie in the 7th and 9th segments. They receive blood from the dorsal blood vessel and convey it to the ventral blood vessel.
The posterior two pairs of hearts are called latero-oesophageal hearts and are situated in the 12th and 13th segments. Latero-oesophageal hearts carry blood from the dorsal vessel and the supra oesophageal vessel to the ventral blood vessel.
There are present two pairs of loop like vessels, the anterior loops in the 10th and 11th segments. They have no valves. They carry blood from the lateral oesophageal vessels to the supra oesophageal vessel.
Blood glands:
These are situated in the 4th, 5th and 6th segments above the pharyngeal gland. They are considered to produce blood corpuscles and haemoglobin. They are analogous to red bone marrow of vertebrates.
Essay # 8. Excretory System of Earthworm:
Excretion is a process through which excretory matter is eliminated from the body of the animal. Earthworms are both ammonotelic and ureotelic.The main excretory organs in earthworm are nephridia (sing, nephridium) which perform the function of excretion and osmoregulation.
The nephridia occur in all the segments of earthworm except in the first two segments. Three types of nephridia are found in the earthworm according to their location, namely the septal nephridia, pharyngeal nephridia and integumentary nephridia. Nephridia are ectodermal in origin.
i. Septal nephridia:
They are present attached to the septa behind the fifteenth segment. Each septum bears about 40-50 septal nephridia attached to its anterior and posterior surfaces. Thus there are 80 to 100 septal nephridia in each segment.
Since the septal nephridia discharge their excretory matter into the lumen of the alimentary canal/enteron, they are called enteronephric nephridia. The opening of the nephridia into the alimentary canal is an adaptation for the conservation of water which is absorbed by the internal epithelial lining of intestine.
ii. Pharyngeal nephridia:
They occur in three pairs of bunches in the 4th, 5th, and 6th, segments lying on each side of the alimentary canal in these segments. Each bunch consists of a large number of nephridia. There are three pairs of ducts which run forwards. The ducts of the nephridia of the sixth segment open into the buccal cavity while the ducts from the nephridial bunches of the fourth and fifth segments open into the pharynx.
These ducts carry excretory matter from the pharyngeal nephriia into the gut (buccal cavity/pharynx). Thus like septal nephridia, the pharyngeal nephridia are also enteronephric nephridia. Enteronephric condition is an adaptation for the conservation of water which is absorbed by the inner lining of the alimentary canal.
iii. Integumentary nephridia:
They are found scattered in the body wall (integument) in each segment except the first two segments. In each segment they number from 200 to 250 except in the fourteenth, fifteenth and sixteenth segments (clitellar region) where their number is about ten times more than that in the other segments.
Thus clitellar segments are often called as the “forest of nephridia”. They are the smallest of the three types of nephridia. These nephridia discharge their contents directly to the outside hence they are called ectonephric (= exonephric) nephridia. Thus they help the earthworm in keeping the skin moist for cutaneous respiration.
Chloragogen cells (yellow cells):
These cells are excretory in function. The chloragogen cells take up excretory matter from the blood capillaries of the gut and from the coelomic fluid of the coelom.
When these cells are filled with excretory matter, they are either taken by the septal nephridia or pass directly to the outside on the surface of the skin through the dorsal pores. They also store glycogen and fat. Thus these cells are analogous to the liver of vertebrates.
Essay # 9. Nervous System of Earthworm:
A group of organs which controls and coordinates the various activities and movements of body parts is known as nervous system. The latter is not very well developed in earthworm. It is divided into central nervous system, peripheral nervous system and autonomic nervous system.
i. Central Nervous System:
It passes through the centre of the body and consists of a pair of supra-pharyngeal (cerebral) ganglia, a pair of peripharyngeal connectives, a pair of sub-pharyngeal ganglia and a ventral nerve cord. The ventral nerve cord has segmental ganglia.
ii. Peripheral Nervous System:
The nerves arising from the central nervous system and supplying the various parts of the body constitute the peripheral nervous system. Two pairs of nerves arise from supra-pharyngeal ganglia and supply the prostomium and buccal cavity. Two pairs of nerves arise from the peripharyngeal connectives and innervate the structures present in first (peristomium) and the second segments.
Two pairs of nerves arise from the sub pharyngeal ganglia and supply branches to organs of third and fourth segments. Three pairs of nerves arise from each segmental ganglion: one pair from the anterior part and two pairs from the posterior part of the ganglion.
These nerves innervate the structures present in the respective segments. All the segmental nerves are mixed in nature i.e., containing both sensory (afferent) and motor (efferent) nerve fibres.
iii. Autonomic Nervous System:
It consists of an extensive nerve plexus situated beneath the epidermis, within the muscles of the body wall and on the alimentary canal. These plexuses are connected with the peripharyngeal connectives.
Essay # 10. Receptors or Sense Organs of Earthworm:
In earthworm there are present three types of receptors:
(i) Tactile receptors:
These receptors are distributed in the epidermis more or less throughout the epidermis of the body wall. But they are more numerous on the lateral and ventral surfaces than on dorsal surface. They are sensitive to touch.
(ii) Buccal receptors:
They are present in the epithelium of the buccal cavity. These receptors are the organs of taste plus smell and are, therefore, also referred to as chemoreceptors.
(iii) Photoreceptors:
They are abundant in the epidermis of the prostomium and peristomium (first segment), while in other segments they are present in lesser numbers. They are not found on the ventral surface.
Each photoreceptor is a single celled (unicellular) structure which contains a nucleus and a clear lens in the cytoplasm. Lens is also called phaosome in earthworm. The cytoplasm has a network of neurofibrils, the retinella from which nerve fibres arise. These receptors detect the intensity of light.
Essay # 11. Reproductive System of Earthworm:
Earthworms are bisexual or monoecious or hermaphrodite ,i.e., both male and female reproductive organs are present in the same individual. But self-fertilization does not occur as the male and female reproductive organs (testes and ovaries) do not mature at the same time. The testes mature earlier than the ovaries.
Such a condition is known as protandry and the animal is called protandrous. The self-fertilization is also not possible in this animal because of the relative position of the openings of male and female reproductive organs. The cross fertilization takes place after copulation. The fertilization is followed by cocoon formation.
Male Reproductive Organs
They consist of the following organs:
i. Testis sacs:
The two pairs of testis sacs are situated in the tenth and eleventh segments. Each testis sac of the tenth segment encloses a testis and a seminal funnel. It also communicates with the seminal vesicle present in the eleventh segment. Each testis sac of the eleventh segment encloses a testis, a seminal vesicle and a spermiducal funnel.
ii. Testes:
There are present two pairs of testes. Immature spermatozoa produced by the testis first enter the cavity of the testis sac and then they make their way into the seminal vesicle where they undergo further development to become mature sperms.
iii. Seminal vesicles:
There are present two pairs of speminal vesicles. One pair lies in the testis sacs of the eleventh segment but it communicates with the testis sacs of the tenth segment. The other pair of seminal vesicles lies in the twelfth segment but it communicates with the testis sacs of the eleventh segment. They store sperms.
iv. Spermiducal funnels:
There are two pairs of spermiducal funnels. Each spermiducal funnel leads into a fine tube, the vas deferens.
v. Vasa deferentia:
There are present two pairs of vasa deferentia. They carry sperms.
vi. Prostate glands:
A pair of large prostate glands is present in earthworm. These glands are situated on either side of the intestine and extend from the 17th to the 19th segment. They produce a secretion, the prostatic secretion which is transferred to outside on the ventral side near the opening of the vasa deferentia. The secretion perhaps serves as a medium for transfer of sperms.
7. Accessory glands:
There are two pairs of whitish rounded glandular masses situated internally in 17th and 19th segments. Each accessory gland opens outside verttrolaterally by several ductless on each genital papilla. The secretion of these glands is supposed to help in keeping the two worms close together during copulation.
Female Reproductive Organs:
i. Ovaries:
There is a pair of white minute masses of the ovaries attached to the posterior surface of the septum present between 12th and 13th segments. Ovaries are larger than testes. They produce ova.
ii. Oviducts:
The oviducts are two short tubes each lying immediately behind the respective ovary. The two ovarian tubes run backwards and converge to meet in the body wall and open to outside by a female genital pore on mid-ventral side of the 14th segment.
iii. Spermathecae:
There are present four pairs of spermathecae which lie in the sixth, seventh, eighth and ninth segments, but anterior parts of all the spermathecae are attached to the septa between 5/6, 6/7, 7/8 and 8/9 segments.
They open to outside through the spermathecal apertures situated ventrolatorally in the successive grooves separating the above mentioned segments. They store the sperms received from another earthworm during copulation.
Essay # 12. Copulation and Cocoon Formation of Earthworm:
The earthworms are bisexual or hermaphrodite or monoecious and protandrous. Thus, cross fertilization occurs, which is accompanied by the copulation. Two worms attach themselves with their ventral surfaces and become opposed to each other in opposite direction.
During copulation male genital papilla of one earthworm is inserted into the spermathecal pore of the other earthworm to transfer the sperms and prostatic fluid.
After copulation two earthworms separate. Now the glandular cells of the clitellum secrete a fluid that forms a girdle around the clitellum. The girdle is filled with mature ova released through female genital pore. The worm wriggles backwards.
When the girdle passes over the spermathecalpores it receives the sperms stored in the spermathecae and albuminous secretion of the epidermal gland cells of skin. Ultimately, the worm wriggles out completely and the girdle is, therefore, left free in moist soil.
Now this structure is called cocoon. Fertilization and development occur inside the cocoon and on an average four baby worms are produced in one cocoon. Other eggs (zygotes) are used as food by the developing embryoes. Development is direct (without larva).It should be noted that the copulation has not been studied in P. posthuma, because it probably takes place deep under the ground.
Essay # 13. Interaction of Earthworm with Mankind:
Earthworms are known as ‘friends of farmers’ because they make the soil loose and porous by their burrowing habit. Thus, the soil provides quick aeration and absorption of water, thereby the roots; of the plant get penetrated easily with water.
Worm castings of the earthworms are of manurial value. The nitrogenous wastes, and other secretions of this worm also form important plant food. The process of increasing fertility of soil by earthworm is called vermin-composting. Earthworms reduce both acidity and alkalinity of the soil and thus, create optimum conditions for plant growth.
Earthworms are also used as food in some countries such as China, Japan, Myanmar (Burma), Australia, etc. They are used as bait for catching the fishes all over the world. Many tribal communities in India use earthworm in the form of medicine to cure bladder stones, jaundice, piles, diarrhoea, etc.
Earth-worm may cause some harm to man. They may damage young and tender paints. During rainy season, they cause soil erosion by making burrows to some extent. They spoil the play-grounds by digging burrows in them. Sometimes, their burrows cause the loss of water from the irrigated lands. Some earthworms serve intermediate hosts for some parasites such as tapeworm of chicken and lung nematode of pigs.
The population of earthworms is declining due to excess use of pesticides and chemical fertilizers. Since many animals such as frogs, lizards and birds eat earthworm, hence these animals are also being affected indirectly and resulting in ecological imbalance.
