Animal life cycles docx

To produce young, some animals have babies, and others lay eggs.. Some baby insects, like bees, look very different from their These baby insects are called nymphs.. Whenthe eggs hat

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Animals grow and change during their tife To produce young, some animals have babies, and others lay eggs These young animals then grow up and produce young, too This journey from being born to producing young is called a life cycle Animal life cycles are amazing.

cycles!

There are mil[ions of different species of animal in the

world Some animats, like the blue whale, are very big.

Others are so small that we almost can't see them.

These animals all have very different life cycles.

Animal Groups

Scientists put animals into groups The animals in

each group are the same in many ways, and they

often have very similar life cycles The two biggest

animal groups are invertebrates and vertebrates

Invertebrates are animals that have no backbone

More than 95% of the animal species in the world

are invertebrates, and most of them are very small

There are many different groups of invertebrates

The biggest group is called arthropods Insecrs,

spiders, and animals like crabs that have a hard

shell, are all arthropods

Animals that have a backbone are called vertebrates

Only a few percent of the animals in the world are

vertebrates, and most of them are much bigger than

invertebrates Because of this, we see vertebrates

more often than invertebrates Scientists put

vertebrates into five big groups - they are called

fish, amphibians, reptiles, birds, and mammals

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All animals need to find food to stay alive Some

animals Herbivores eat plants, and omnivores eat

plants and animals

There are many dangers for animals They have to

keep safe from predators - animals that hunt and eat

other animals People hunt birds and other animals

People also cut down trees and build houses and roads

on land \When they do this, animals lose their homes

and their food Many animals also become sick or die

because of pollution of the land, oceans, rivers, and

air Life is very dangerous for animals Many animals

die before they are old enough to produce young

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Males produce sperm, and females produce eggs.llaby animals are made when sperm from the maleyoins together with an egg from the female This iscalled fertilization

Some animals give birth to baby animals Other

hatch - they break the egg open and come out

Most reptiles and birds care for their babies Mostinsects and fish do not care for their eggs or their

them milk Some big mammals stay with theirbabies for many years

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Insects are sma[[ animals [ike butterflies, beetles, flies,

bees, and ants There are more than a million species

of insect in the world Many insects change in amazing

ways during their [ife.

Almost all insects start their life in an egg The young

insect grows inside the egg and then it hatches Some

baby insects, like bees, look very different from their

These baby insects are called nymphs Larvae and

nymphs are very small when they hatch

A young insect eats a lot of fooCand grows very quickly It has ahard cover, called an exoskeleton

lirr the young insect, it breaks openand comes off A new exoskeletongrows under the old one This iscalled molting

Some insects grow wings that get bigger every timethey molt After the insect molts for the last time, itbecomes an adult that can fly and produce young.'l'his is called incomplete metamorphosis

Most insects change by complete metamorphosis.When the larva is ready to change into an adult, itscxoskeleton comes off Under the exoskeleton there's

a pupa - it's like a closed case Inside the pupa, anamazing change happens The larva changes into

an adult that looks completely different!

When insects become adults, they are ready to breed

and produce young First they need to find a mate

females that they can mate with

Female butterflies and moths produce special chemicals

butterflies and moths can smell the pheromones from

Some insects only lay a few eggs during their life,but others lay thousands Many insects are careful

to keep their eggs safe The cardinal beetle makes

a hole in dead wood and lays her eggs inside Whenthe eggs hatch, you can't see the larvae very well.Cockroaches lay their eggs in a special case, andbeetle eggs are usually yellow, green, or black sothat they are camouflaged When these insect eggshatch, the life cycle starts again!

There are many other groups of invertebrate, and they

a[[ have very different life cyctes Did you know that

earthworms, octopuses, spiders, and tobsters are a[[

invertebrates?

All earthworms lay eggs, because they are

male parts that produce sperm and female parts

that produce eggs, but they cannot fertilize their

make special rings with eggs inside The ring moves

forward over the worm's body and then it comes

off Then the ends of the ring join together The

eggs hatch after about three months, and young

earthworms can mate when thev are 12 months old

Baby octopuses live in the open ocean at first, butwhen they grow, they move down to the bottom ofthe ocean Here they live on their own in dens

Octopuses are ready to mate when they are one

or two years old Some female octopuses lay about200,000 eggs, and many put them in strings from thetop of their dens The females keep the eggs safe frompredators and they carefully push water over them so

for up to ten months when they are caring for theireggs.After the eggs hatch, the female octopuses die

Spiders produce silk, and they use it to make webs,

where they catch flies and other insects Most species

of spider also put lots of silk around their eggs ro make

a special cover, called a cocoon

a few times They can soon make their own webs and

catch their own food

only about ten of them will live The female lobstercarries her eggs hidden under her tail for almost ayear When they are ready to hatch, she lifts her tailand they float away

When the eggs hatch, the larvae move to the top of the

and difficult currents Lobster larvae look very different

molt about 25 times before they become adults

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Fish are vertebrates that are cotd-blooded This means

that their body is as hot or cold as the water around

them Att fish live and breathe in water, and most

baby fish hatch from eggs.

Female fish can lay hundreds of eggs Inside every egg

there's a bag of food called the yolk The unborn baby

fish eats the yolk, so that it can grow bigger and stronger

trish often try to hide their eggs because many

other animals like to eat fish eggs Female seahorses

lay their eggs into a special pouch on the male's front,

where they stay safe until they are ready to hatch

Some species of shark lay their eggs in a hard egg case

their body The young fish use this as food at first.Life is very dangerous for young fish Most of themdon't have fins, so they can't swim well They oftenfloat into colder water or places where there's no food.Alsc-r, many prcdators, like seals, birds, frogs, and othcrfish, l-runt them This is why fish lay so many cggs Alarge female tuna fish can lay up to six million eggs atone time, but only about twcl of these will grow intoadult tuna!

Most fish never see their parents because they swim

away after they have laid their eggs.The young fish

have to find food for themselves so that they can grow

bigger They eat small plants and insect eggs or larvae

Most small fish grow into adults just a few months

after hatching, but whale sharks do not grow into

adults until they are 25 years old!

l;ish need to find mates so

t l r a t t h e y c a n b r e e d ' W h e nthc male three-spinedstickleback is ready to breed, he builds a nest

l'art of his body changes to a red color Females seehis bright colors and they lay their eggs in his nest.Many fish go back to the same place to breed everyyear Salmon live in the ocean, but to breed, they swimback to the rivers where they hatched Some salmontravel hundreds of kilometers up rivers, and sometimesthey have to jump up waterfalls They change colorfrom silver to red when they are swimming back totheir breeding places

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Like fish, amphibians are cotd-blooded vertebrates.

Most amphibians live for

and for some of their life

All amphibians have two different parts of life At first

they are larvae that breathe in water through special

gills Then they change into adults with lungs This

change is called metamorphosis Usually, amphibians

live in water for the first part of their life and on land

for the second part Some salamanders live in water

all the time

some of their life in water

on tand Salamanders, toads,

a n d fr o g s a r e a [ [ a m p h i b i a n s

Amphibians often lay thousands of eggs The eggs have

a sticky cover, and they float in water Most amphibians

do not care for their eBBS, but the male midwife toadcarries them on his back until they are ready to hatch.The young that hatch from eggs are called larvae, butyoung frogs and toads are also called tadpoles At first,tadpoles don't have legs or feet and they breathe throughgills It's easy for predators to catch and eat eggs andtadpoles Frogs can lay about 2,000 eBBS, but probably

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Becoming Adults

When amphibians begin to change into adults, they

grow lungs inside their body and their gills close At

the same time, most amphibians grow legs and feet

An adult frog looks completely different from a tadpole!

Most adult amphibians can breathe through their skin

and their lungs!They can only breathe through their

skin if it's wet, so most amphibians live near water

Amphibians are cold-blooded, so when it gets very

cold they have no energy Some amphibiairs in colder

countries hibernate for the winter They hide in a safe,

wet place and go into a special, long sleep

Amphibian tarvae are herbivores, but during

Breeding

Most amphibians go to wet places like ponds, lakes,

or rivers to breed, because their eggs and larvae live inwater Many go back to the same place every year, andsome go back to the pond or stream where they wereborn Male frogs croak and shout to tell the femalesthat they are ready to breed They push their throatsout so that their calls are louder \(rhen the female haschosen a mate, she lays her eggs in the water, and themale covers them with sperm

Reptiles are cold-blooded, and their skin is dry and

covered with special scates Lizards, snakes, crocodiles,

attigators, and turttes are a[[ reptiles Some live on [and

and some live in water.

Most reptiles hatch from eggs, but a few are born as

living animals Females lay their eggs in a warm, wet

place They usually lay a lot of eggs, but many eggs

are eaten by predators Most reptiles lay their eggs

and then they leave them, but pythons put their body

around their eggs to keep them warm Alligators make

and stay near the nest They don't eat for weeks when

they are keeping their eggs safe

Crocodiles and alligators are very good parents aftertheir eggs hatch The female Nile crocodile is verycareful - she puts her babies inside her mouth to carrythem to water She stays near them to keep them safefor up to two months

\fhen snakes and lizards grow, they get too big fortheir skin The old skin comes off and there's a new

lose their old skin three or four times everv vear

When reptiles are readv to brced, thcy have to find

a mate Male crocodiles lift their head up and make

a loud sound They also blow bubbles in the water

so that females will sec and hear them Snakes find

their mate by smell The females leave a special

smell that the male follows Other male reptiles, like

monitor lizards, fight each other for a mate The

Reptiles arc in danger from manv predators, and tl-tc1,have lots of ways of keeping safe If a prcdator catchcs

a lizard by its tail, the hzard can break its tail off andcscape It then grows a new tail The stinkpot turtlemakes a horrible smell from its legs to make predators

go away Many reptiles also use camouflage to keep

s a f e S o m e c h a m e l e o n s c a n c h a n g e c o l o r s o t h a tpredators do not see them, and the leaf-tailed geckocan hide easilv becausc its bodv looks like a leaf