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Invertebrates

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 There are nine phyla in invertebrates. Out of those nine phyla, the phylum Arthropoda consists of a large number of insects, among which insects like silkworm and bees are useful insects. The larvae of a silk moth secrete the silk thread which is used to make clothes. Honey bees produce and store honey which is nutritious food.

Silkworm                                                                                    

Silkworm is one of the important insects which forms a quality of fiber called silk. It is obtained from the cocoons of the silkworms which is important from the commercial point of view. The important two types of silkworm are ERI Silkmoth (Attacus ricinii) and SERI Silkmoth (Bombyx mori). ERI silkmoths feed on caster leaves and SERI silkmoths feed on mulberry leaves. The position of silkworm in classification chart is as follow:

Classification

                Kingdom              : Animalia

                   Sub- Kingdom : Invertebrate

                      Phylum           : Arthropoda

                         Class             : Insecta

                            Common Name    : Silkworm/ Silkmoth

External Structure of Silkworm

Silkworm is a creamy white colored insect which is about 2-3 cm long and shining in nature. The body of a silkworm is divided into three parts: head, thorax, and abdomen. The head consists of a pair of feathery antennae, a pair of compound eyes and the mouth which has a sucking type of structure. The thorax consists of three types of legs and two pairs of wings which are about 25 mm in length covered with scales. The abdomen is a hairy part which consists of ten segments covered with minute scales. The body of a female silk moth is wider than the male silkmoth as it contains a number of eggs. Adults don’t feed and they are weak at flying.

Silkworm
Silkworm is a unisexual insect. The female silk moths are larger than the male moths. The adult moths are primarily concerned with reproduction and they seldom eat. The male and female moths mate in the tail to tail position and fertilization is internal. The male moth dies immediately after mating. The life cycle of a moth completes in 45 days.

  1. Egg: The female lays about 300 to 400 eggs in clusters upon mulberry leaves immediately after mating which takes about 1-24 hours to complete. The female moths stick to the leaves with a gelatinous secretion. They die after 4-5 days after laying the eggs. The eggs, in the beginning, are white in color, small pinhead sized and later change into grey as the days pass by. If the mulberry leaves are not available, the eggs are stored in a cold place to prevent them from hatching. When the eggs are placed at the temperature of about 18⁰C to 25⁰C, the larva emerges out from the eggs within 10 to 12 days.
  1. Larva: A silk moth passes through five stages during the larva phase of its life which is called instars. During the first instars, the larva comes out from the egg which is grey in color and the body has twelve segments. It feeds on mulberry leaves and grows very quickly. It stops feeding after 4 to 5 days and becomes inactive. Then the first instar moults which occur 4 times at the age of 6th, 12th, 18th and 26th days respectively. After each moult, the instar grows rapidly. During moulting, it stops feeding for 20 to 24 hours. After the 4th moult, a pair of silk glands, which is a long sac-like structure, develops on the lateral side of the body on the fifth instar. The silk glands secrete a sticky kind of fluid which becomes hard and fine thread when it comes in contact with air. The larva caterpillar gets enclosed in the fine thread, which actually forms a case around its body, this is said to be cacoon. The cocoon is white or yellow, thick oval capsule shaped structure. The caterpillar larva changes into the chrysalis. It takes about 25 to 32 days to complete the whole life cycle of a silkworm.
  1. Pupa: The pupa is the inactive stage of the life cycle in which the body is protected in a cocoon which undergoes very important active changes called metamorphosis. It stops feeding but shows the internal development. The stage of pupa completes in about 12 to 14 days. The silk fiber is obtained from the cocoon of the silkworms which is about 1000 meters. The silk is obtained by keeping the cocoons in boiling water or a hot oven to destroy the glue present in it. Then the silk fiber is unwounded from the cocoons.

  2. Adult: The pupa changes into an adult silk moth after the active metamorphosis. The imago (adult silk moth) breaks the cocoon for coming out. After drying the wings, it can fly. It survives for about 5 to 7 days after coming out from the cocoon. After the maturity of the female silk moth, it lays eggs.

Hence, the whole life cycle of a silk moth completes in about 45 to 50 days.

Economic Importance of Silk

Silkworm is one of the beneficial insects as the silk produced from the thread of cocoon in the fifth stage is used for commercial purpose. The process of rearing the silk moth on a commercial basis is called sericulture. Some of the major importance of silk are listed as follow:

  1. Silk clothes are best suited for every season. It is used for making clothes, curtains, etc.
  2. A new effect in fabrics can be achieved by combining silk with other natural and synthetic fibers.
  3. The surgical strings, fishing strings, etc. can be made from the silkworm.
  4. The economic status of the individual and nation can be improved from sericulture.
  5. Silk garments are light in weight and warmer than other clothes.

Characteristics of Silk

  1. Silk is known as the queen of fibers as it is soft, strong, durable and shiny fiber compared to other natural and synthetic fibers.
  2. Silk is one of the strongest fibers compared to other fibers.
  3. Silk is elastic in nature as it will return to its original shape even after being stretched.
  4. Silk is used in surgical stitching as it does not decay easily.
  5. Silk absorbs water easily.

Honey Bee

Honey bees are also one of the useful insects like silkworms. They are always busy and work in coordination to produce and store honey. They make a colonial nest using wax under which all their tasks are undertaken is said to be a beehive. The study of bees including honey bees is known as melittology. The position of the honey bee in a classification chart is as follow:

Classification

                Kingdom              : Animalia

                   Sub- Kingdom : Invertebrate

                      Phylum           : Arthropods

                         Class             : Insecta

                            Genus       : Apis (Bee)

We can find three kinds of honey bees in a colony which is specified to perform certain work determined by their age and gender. The three categories of honey bees are:

    Egg laying female or Queen Bee

    A few hundred males or drones

    20 to 80 thousands of sterile females or workers               

The Queen

The body of a queen is recognized by the head, thorax, and abdomen. The queen has got a large abdomen. The queen bee lives for 2 to 5 years. When the life of the queen comes to an end one of her daughters takes over the colony. She is the only one who lays the egg and does not involve in collecting nectar and pollen but helps in the production of offspring.

The Drones

The drones are the fertile male bees. Their body is also divided into head, thorax, and abdomen. They are smaller than queen bee and bigger than the workers in size. Their life ends in about 4 to 5 weeks. They are fed by workers and they help queen in the fertilization process. After mating with the queen, they are turned out of the hive where they die immediately as they are not able to find the food for themselves.

The Workers

The sterile female bees are known as workers. Their body is also divided into head, thorax, and abdomen. They are small in size and they do not lay eggs. They can easily collect nectar from the nectarines as their mouthparts are adapted for chewing and lapping. They have three pairs of legs covered with hairs which consist of a pollen basket to collect nectar. They are the busiest and hardworking bees. They help in taking care of the larvae produced by the queen, regulate the temperature in the colony and collect the nectar and pollen. They also help to make the hive and protect the colony from enemies. They live for about 6 weeks.

External Structure of a Bee

The body of a honey bee is covered with cuticle which forms an exoskeleton that provides support for muscles and allows their fast and precise movement. It also prevents water loss from their body. The body of a bee is divided into head, thorax, and abdomen.

The head of a bee consists of a pair of compound eyes, three ocelli i.e. simple eyes, a pair of antennae, sensory bristles and mouthparts. A pair of compound eyes has covered much space of the head as each eye is made up of 6000 facets that perceive shapes, colors, motion, and distance. There are three ocelli located at the top of the head which help them to respond to the change in light and darkness, leading to flight stability. The head also consists of a pair of antennae which has 13 segments in male and 12 segments in the female. The antennae have many hairs like structure that helps to detect air movement so as to hear sounds, smell and taste. The mouth part of bees are chewing and sucking type which contains mandibles or paired teeth which help in chewing the pollen, manipulate wax, attack intruders, and clean other bees. Proboscis or labium or tongue is a long and slender structure which helps in sucking up nectar from nectarines of the flowers. When there is no use of proboscis, it gets folded back under the head by leaving the stouter mandibles free which is used for chewing.

The part of the body which connects the head to the abdomen is known as thorax. It consists of three segments: prothorax, mesothorax, and metathorax. The prothorax consists of one pair of forelegs; the mesothorax consists of one pair of middle legs and one pair of forewings, and metathorax consists of one pair of hind legs and one pair of hind wings. Thus, the thorax is considered as the point of attachment for all three pairs of legs and two pairs of wings. The hind wings of workers are highly specialized having long curved hairs and a pollen basket in order to collect and transfer pollen.

The third part of the body; the abdomen is a long and broad part which consists of nine segments. The queen bee has a large abdomen.

Life Cycle of Bee

The life cycle of a bee goes through four stages: egg, larva, pupa, and adult. The colonies of bee are perennial which consists of three castes: queen, drones or males, and worker bees.

When the queen becomes incapable of laying eggs or dies, the worker bees raise a new queen for the hive among them who can lay eggs. The new young queen becomes capable of mating and when the mating is completed the drone dies. After the mating, all sperm is stored in the sperm sac of the queen which lasts for two or more years of egg-laying that releases with each fertilized eggs. Even after all the stored sperm is finished, the queen can lay the unfertilized eggs. The fertilized eggs hatch into the new worker bees or queen bees whereas the unfertilized eggs hatch into drones.

  1.  Egg: The queen can lay up to 3000 pin-head sized eggs in a single day. Before placing them into a hexagonal wax cell of the honeycomb, she examines each egg carefully and packs them closely together within cells. It takes about three days to hatch the eggs into larva.

  2. Larva: The larvae resemble the grain like structure which is white colored microscopic in size without eyes and legs. But it has got a mouth whose sole function is to eat and grow living inside the brood cell. The worker bees are the ones who can decide which larve should become drones and which should become queen. It depends on feeding to the larve by the workers.
    All the larvae are fed on a special bee secretion diet called royal jelly for three days. After seeing the progress in three days, the worker bees decide which larva is going to develop in queen bee and which is going to be drones or workers bee. They are fed accordingly, the queen bee is fed royal jelly and others are fed the mixture of honey, water, protein, and pollen. So, the development of bees differs from one to another. The larvae change their skin 4 to 5 times as they grow up, when the larvae stop eating, they form a cocoon and starts to take the structure of a pupa on about 6th day. They are secured by the workers in brood cells.

  3. Pupa: The bees begin to develop legs, eyes, and wings in the pupa stage. After the maturity of the pupa stage, they chew their way out from the cells and become the adult bees. The time duration for each pupa to change into adult differs from one to another. It takes 7.5 days for a queen bee, 12 days for workers and 14.5 days for drones to become adult from the pupa.

  4. Adult: When the bee reaches the stage adult, it becomes fully grown up and ready to accomplish their tasks. A typical colony of bees consists of 50000 to 60000 worker bees, 600 to 1000 drone bees and only one queen bee.

A brief discussion of all three types of bees are as follows:

Types of Bees Lifespan Egg Larva Pupa Time duration for the completion of life cycle No. of Bees/ Colony Functions or Purposes
Queen About 2-3 years 3 days 5.5 days 7.5 days 16 days 1 Lays eggs
Worker About 6 weeks 3 days 6 days 12 days 21 days 10000 to 60000 Nurse the brood, clean the colony and forage for food
Drone About 4-5 weeks 3 days 6 days 14. days 23.5 days  100 to 500 Mate with the queen


Economic Importance of Honey Bee

  1. Honey bees are environmentally friendly and the honey extracted by honey bees can be used for commercial purpose.
  2. The wax produced by bees are used to make toiletry and goods such as candles, creams, etc.
  3. Honey is a good source of vitamin and functions as antioxidants. It is good for humans.
  4. Honey contains different types of minerals and vitamins which are essential for the growth and development of living beings.
  5. Bee helps in cross-pollination as they travel from one flower to another while collecting nectar.
  6. Bee farming or beekeeping helps to improve the economy of the nation.

 

 



  1. Silkworms are very beneficial insects from the commercial point of view.
  2. Eri silkworms that feed on caster leaves and seri silkworms that feed on mulberry leaves are two types of silkworms that are reared in Nepal.
  3. Silkworms complete their life cycle in about 45 days.
  4. The male silkworms die after copulation and female silkworms die after laying eggs.
  5. Bees can be categorized into three types: Queen bee, Workers and Drones or Males.
  6. The queen bee lays egg and is bigger than other bees in the hive.
  7. Workers are smallest bees who do the work of making the hive, collecting nectar and feeding the larvae.
  8. Drones or males are the bees who help the queen in the fertilization process. They die after mating.
  9. The life cycle of bees and silkmoth goes through four stages: egg, larva, pupa, and adult.
  10. Honey produced by honey bees are beneficial to living beings from both commercial and nutrition point of view.

 

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Very Short Questions

The major economic importance of silk are:

  1. Silk clothes are best suited for every season. It is used for making clothes, curtains, etc.
  2. A new effect in fabrics can be achieved by combining silk with other natural and synthetic fibers.
  3. The surgical strings, fishing strings, etc. can be made from the silkworm.
  4. The economic status of the individual and nation can be improved from sericulture.
  5. Silk garments are light in weight and warmer than other clothes.

Silkworm is called the queen of fibres because it forms a quality fibre which is shiny, strong, long and attractive.

The cocoon of a silkmoth is kept in boiling water or a hot oven in order to destroy the gelatinous substance present in it. It helps to extract the silk thread easily.

Honey is good for human beings because of many nutrients such as vitamins, proteins, sugar, etc. that are necessary for the healthy growth and development of the body is obtained from honey.

The process of rearing silkworms for cocoons on commercial basis is known as sericulture.

Worker Bee:

Worker bees are the smallest sterile female bees that make the hive, protect their hive and queen bee from the enemies, regulate the temperature of the hive, collect the pollen and nectar to produce honey and feed the developing larvae.

The two types of silkworms found in Nepal are:

  1. ERI Silkmoth (Attacus ricinii)
  2. SERI Silkmoth (Bombyx mori)

ERI Silkmoths feed on castor leaves. SERI Silkmoths feed on mulberry leaves.

The major economic importance of honey bees are:

  1. Honey bees are environmentally friendly and the honey extracted by honey bees can be used for commercial purpose.
  2. The wax produced by bees are used to make toiletry and goods such as candles, creams, etc.
  3. Honey is a good source of vitamin and functions as antioxidants. It is good for humans.
  4. Honey contains different types of minerals and vitamins which are essential for the growth and development of living beings.
  5. Bee helps in cross-pollination as they travel from one flower to another while collecting nectar.
  6. Bee farming or beekeeping helps to improve the economy of the nation.

 

The summary of three kinds of bees is as follow:

Types of Bees Lifespan Egg Larva Pupa Time duration for the completion of life cycle Number of bees/ colony Functions/ Purposes
Queen About 2-5 years 3 days 5.5 days 75 days 16 days 1 Lays eggs
Worker About 6 weeks 3 days 6  days 12 days 21 days 10000 to 60000 Nurses the brood, safeguard the hive, collect nector
Drone About 4-5 weeks 3 days 6 days 14.5 days 23.5 days 100 to 500 Mating with queen

Honey bees are vital pollinators because they help in cross-pollination and ensures the fertilisation in different types of flowers.

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  • What kind of food do seri- silkworms eat?

    castor flower
    banana leaves
    castor leaf
    silk plant
    mulberry leaf
    mulberry flower
  • What is called the study of silkworm?

    silkology
    silkworm study
    silkculture
    agriculture
    sericulture
    melittology
  • How many time a silkworm larva moult?

    10 times
    5 times
    4 times
    16 times
    12 times
    2 times
  • For how long does a queen bee live?

    10 months
    2-5 months
    6 weeks
    up to 10 years
    24 hours
    2-5 years
  • How much honey can a single honey bee makes in its life time?

    about \(\frac 1{12}\)th of table spoon
    about a table spoon
    about \(\frac 1{12}\)th of a tea spoon
    about 1 kg
    about 500 gms
    about \(\frac 12\) of a tea spoon
  • The life cycle of a silkmoth completes in about ______.

    54 days
    8 days
    85 days
    45 days
    102 days
    10 days
  • Larvae of a honey bee is fed on a special bee secretion called ______.

    fruit juice
    honey
    apple
    fruits
    leaves
    royal jelly
  • The time duration for the completion of life cycle of a worker be is ______.

    23.5 days
    7.5 days
    32 days
    8 days
    16 days
    21 days
  • The male silkworm dies after ______.

    none of them
    sleeping
    laying egg
    coming out of larvae
    extracting silk
    copulation
  • A silkmoth passes through five ______ during the larvae phase of its life.

    metamorphosis
    sericulture
    instars
    imago
    moulting
    cycles
  • ______ is the only insect that produces food eaten by humans.

    Ladybird
    Honey bee
    Silkworm
    Cockroach
    Butterfly
    Ant
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