Animals: Common Insects Chapter Notes | Science Class 3 ICSE PDF Download

Introduction

Body Parts of an Insect

• Insects lack bones; their body is covered by a hard exoskeleton made of chitin.
• Exoskeleton provides protection, support, and flexibility.
• Insect body is divided into three parts: head, thorax, and abdomen.

Head

• Contains a pair of antennae, compound eyes, and mouthparts.
• Antennae are sensory organs for detecting smells, tastes, vibrations, and sounds.
• Compound eyes, made of many small eye units, help track fast-moving objects.

Mouthparts vary based on food type:

• Grasshoppers and beetles have biting and chewing mouthparts.
• Butterflies and moths have siphoning mouthparts for nectar.
• Mosquitoes have needle-like mouthparts to suck blood or plant juices.
• Ants have strong jaws for digging and collecting food.

Thorax

• Middle part of the body, divided into three segments.
• Has three pairs of legs, one pair per segment.
• Legs are adapted for walking, swimming, jumping, digging, or grabbing.
• Leg tips have sticky pads, hooks, or suckers to cling to surfaces or hold prey.
• Insects breathe through spiracles (openings) on thorax and abdomen; number varies by species.
• Most insects have two pairs of wings; some, like flies, have one pair; others, like ants and fleas, have none.

Abdomen

• Usually has 11 segments.
• Contains digestive, excretory, and reproductive systems.
• May include special organs like stingers.

Life Cycle of an Insect

• Life cycle is the series of changes an insect undergoes during its lifetime.
• Starts with an egg, hatches into a larva, and develops into an adult.
• Some insects have three stages; others, like butterflies, have four: egg, larva, pupa, and adult.

Life Cycle of a Butterfly

• Adult butterfly lays eggs on plant leaves.
• Eggs hatch into larvae (caterpillars), which eat leaves and grow.
• Caterpillars shed skin multiple times as they grow.
• Fully grown caterpillars form a hard case (pupa).
• Inside the pupa, major changes occur.
• After a few days, adult butterflies emerge from the pupa.
• Insects with three-stage life cycles skip the pupa stage.

Social Insects

• Some insects live in groups called colonies for protection, food, work, and shelter sharing.
• Examples include ants, bees, wasps, and termites.
• Ants and bees live in well-organized colonies with a queen, a few males, and many female workers.
• Only the queen lays eggs.
• Ants build nests in dirt, sand, or logs; found in kitchens, windowsills, near trees, or parks.
• Bees live in hives, often in orchards, gardens, or tree cavities; hive size depends on season and food supply.

Useful Insects

• Bees provide honey and beeswax, used for candles, soaps, skin products, and crayons.
• Silkworms produce silk.
• Some insects spread seeds, helping new plants grow.
• Beetle larvae clean the environment by eating dead plants and animals.
• Dragonflies control mosquito populations.
• Dragonflies are harmless, do not sting or carry diseases.

Harmful Insects

• Some insects cause harm by spreading diseases or damaging crops, food, books, furniture, and clothes.
• Examples include mosquitoes, termites, lice, cockroaches, houseflies, and bedbugs.
• Mosquitoes bite to suck blood, spreading diseases like malaria, dengue, and chikungunya.
• Termites eat wood, damaging furniture and buildings by digging tunnels.
• Lice live on human scalps, causing itching by sucking blood.
• Cockroaches, active at night, carry germs near waste or food, causing dysentery and allergies.
• Houseflies transfer germs to food, causing stomach infections.
• Bedbugs, found under sofas or mattresses, cause skin rashes by biting.
• Wasps and bees can sting painfully.
• Female Anopheles mosquitoes spread malaria.

Remedies to Prevent Harmful Effects of Insects on Humans

• Apply ice packs to reduce redness and pain from insect bites.
• Avoid scratching bites to prevent infection.
• Use home remedies like ice packs, aloe vera, mint, or used tea bags to relieve itching.
• Calamine lotion can help reduce itching from bites.

Ways to Keep Insects Away

• Keep drains in kitchen and bathroom clean.
• Ensure garbage cans are tightly closed.
• Prevent standing water during the rainy season.
• Use insect repellents on clothing, shoes, or mosquito nets.
• Wear light-colored, long-sleeved shirts and full pants to avoid mosquito bites.
• Use insecticides and pesticides to kill insects.
• Use natural methods like dried neem leaves in clothes or neem/kerosene oil on furniture.
• Spray lemon juice, vinegar, or use mint to repel ants and flies.
• A pest is an insect or animal that damages plants, trees, or food.

Terms to Know

• Insects: Small animals with six legs.
• Exoskeleton: Hard outer covering of an insect’s body made of chitin.
• Chitin: Strong substance forming the exoskeleton.
• Antennae: Long sensory organs on an insect’s head.
• Compound eyes: Eyes made of many small eye units.
• Thorax: Middle part of the body with legs and wings.
• Abdomen: Lower body part containing digestive, excretory, and reproductive systems.
• Social insect: Insect living in a well-organized colony with others of its kind.
• Nocturnal insects: Insects active at night.