The Most Successful Animals on Earth
Scientists call insects the most successful animals on
Earth. Of all the millions of animals on our planet, eight out of every ten
are some kind of insect. Insects are arthropods that
have six jointed legs. Insects live in deserts, forests, grasslands, mountains,
and cities. Some even live in aquatic environments,
like freshwater ponds, lakes, and streams. Some live underground, others fly
through the treetops. Most are less than 1
cm long. But a few, such as tropical stick insects, are giants. Some of
the most well known insects are butterflies, beetles, dragonflies, cockroaches,
and social insects like ants,
termites, and bees.
What's Their Secret to Success?
Insects come in many sizes, but all have a very special role in keeping
the environment healthy.
©M.Durham/GLOBIO.org Earth is home to an unimaginable number of
insects. For example, just in a small patch of tropical
rainforest about the size of one and a half city blocks there may be over
8 million ants! Plus, scientists discover about 7,000 new insect species each
year. One reason insects have been so successful in surviving and multiplying
is that they are small. They don’t need much living space. They can live
under rocks and wood, in flowers, and even in TVs! In fact, species of insects
are adapted to live just about everywhere.
Ancient Creatures
Insects are one of the oldest groups of animals
on Earth. Fossils of ancient insects have been found in a clear, honey-colored
substance called amber. These fossilized insects are over 400 million years
old. Scientists believe insects and flowers evolved together because insects pollinate most
plants on Earth. Insects were the first animals to fly. In fact, even today,
insects are the only arthropods that can fly.
A Short Life with Many Changes
Butterflies and moths metamorphose from crawling caterpillars into beautiful
flying insects.
©G.Ellis/GLOBIO.org Most insects develop through three stages
in their short lives: egg, larva,
and adult. Some have one more stage between the larva and adult stages. This
stage is called the pupa,
or metamorphosis stage.
The best-known metamorphosis occurs when butterfly and moth caterpillars change
themselves into flying adults. Many other winged insects such as beetles, bees,
and flies also go through a dramatic metamorphosis.
Slow Starters and Quick Finishers
Cicadas are one of the slowest developers of all insects. Some species that
live in North America take 17 years to become adults. During that time they
stay hidden below ground or under leaf litter. They emerge fully grown with
developed wings. Great swarms of them fly off together to search for mates.
The tiny fruit fly develops more quickly. It takes less than two weeks to mature.
Insect Anatomy
All insects have three main body parts: the
head, thorax (middle),
and abdomen (rear).
The outside of their bodies is covered with hard, waterproof armor called an exoskeleton.
Click on the photo below to discover how an insect works.
A Six-Legged Feast
Most insects feed on plants and other insects. Some have very specialized
legs and mouthparts designed just for the food they eat.
©G.Ellis/GLOBIO.org When it comes to food, insects will eat almost
anything - including each other! Most insects eat plants and
other insects. In fact, if it were not for insects hunting each other for a
meal, the world would probably become overrun with insects in just a few days.
Some insects have very specialized eating habits. Praying
mantids have extra-large front legs for capturing other insects. Their
jaw-like mandibles crush
and chew the crunchy exoskeletons of their insect prey.
Female mosquitoes have a straw-like mouth with a drill and sucking tube for
getting blood and other liquids out of animals.
Coping With Cold Temperatures
All insects are cold-blooded.
This means they must warm their bodies using energy from the sun.
In the winter or in cold locations, some insects remain inactive until it becomes
warmer again.
Migration: Getting Away From it All
Others migrate to
a warmer environment. Butterflies are champion fliers. Some species such as
the monarch
butterflies of North America migrate very great distances. Each year, millions
of monarchs travel up to 3,500
km to spend the winter in Mexico where it is warmer.
A Big Role for Tiny Animals
Insects are important pollinators. They help flowers, fruit, vegetables,
and other plants spread and grow.
©M.Durham/GLOBIO.org Insects may be small, but they're very important
to all life on Earth. Without insects, we might not have the fruits and vegetables
we’re used to eating. In most environments, insects are critical to plant
growth because they pollinate flowers. Without pollination, fruits and many
vegetables will not form.
Insects also carry seeds to new places where they can grow. They help keep
soils healthy by turning over and aerating the
soil. Some insects create small compost piles
with their nests, which add nutrients to the soil.
Pesky Insects
Many insects help make life on Earth possible
for other animals and plants and much better for all of us. But there are a
few insect species that most people might like to live without. Flies, fleas,
and mosquitoes, for example, can make your life uncomfortable. But they, too,
have their role in the environment.
Deadly Spreaders of Disease
Some insects that puncture the skin and suck blood or fluids out of their
victim can be very dangerous to people. They do not kill people directly, but
they may carry diseases like malaria, typhus, or dengue
fever. Of all insect species, mosquitoes are the most dangerous to people.
Malaria carried by certain kinds of mosquito infects over 300 million people
a year. Malaria kills more than 1 million people each year.
Some insects have a nasty bite or sting that can make people feel itchy
and sick.
©G.Ellis/GLOBIO.org