Insect


Insect
Insects are a group of invertebrate animals and are part of the phylum Arthropoda. They are the biological class Insecta'". Some people call insects "bugs", but this is not right; insects are insects, not "bugs". Only some insects are true bugs, which is a special group of insects.
Insects are the biggest group of animals on earth, and there are more than 800,000 different kinds (or species) of them. There are often new species of insects being found, and scientists think there are millions of species people have not found yet. There are more insects than all other kinds of animals.
Insects live all over the planet, but not many insects live in the oceans or in very cold places, such as Antarctica. The most kinds of insects live in tropical areas.
The science of insects is called entomology, and people who study insects are called entomologists.
Insect bodies.
Insects have exoskeletons (skeletons on the outside). This does not mean they have bones on the outside of their bodies. Their skeletons are made out of thin, hard pieces or plates, like armour. All together, these pieces make a hard layer around the insect’s body. The exoskeleton protects the insect. Just like our muscles connect to our bones to make us walk and stand up, the muscles of an insect connect to the exoskeleton to make it walk and move.
The body of an insect has three main parts: a head, a thorax, and an abdomen. On the head are an insect’s eyes, its antennae (they feel and smell things), and its mouth. On the thorax, insects have wings and legs. All insects have six legs (three pairs) and usually four wings (two pairs). The abdomen is the back part of the insect. Inside the abdomen is the stomach, the heart, and the excretory system where body wastes pass out of the insect. Bees also have a stinger at the back of the abdomen.
How insects grow.
Insects grow very differently than people. Most insects start as an egg that a female (mother) insect lays. These eggs are very small; many can not be seen without special help, such as a magnifying glass or a microscope.
After the eggs hatch, there are two different things that can happen. Some insects have what is called incomplete metamorphosis. This means that a small insect, called a nymph comes out of the egg, and the nymph looks almost the same as the adult insect. As the nymph grows, it does not change the way it looks, but only how big it is. Grasshoppers grow in this way.
Other insects have complete metamorphosis, which means that the small insect that comes out of the egg looks very different from the adult insect. Insects that have complete metamorphosis usually come out of the egg as a larva, which usually looks like a worm. The larva eats food and gets bigger until it turns into a pupa. Butterfly pupae (plural for pupa) are often inside cocoons. Inside the cocoon the insect changes the way it looks and often grows wings. When the cocoon opens, the adult insect comes out. Many insects have complete metamorphosis, for example beetles, butterflies and moths, and flies.
Kinds of insects.
Contrary to what some people believe, spiders, scorpions, and similar animals are not insects; they are arachnids. Arachnids are arthropods that have 4 pairs of legs. Centipedes are arthropods with many legs and are also not insects.
Insects and people.
People often think of insects as being either good or bad. “Good” insects are beneficial to people, meaning they do things that help people. “Bad” insects are called pests.
Pest insects can be harmful to people in different ways. Some are parasites, such as lice and bed bugs. Some of these parasite insects can spread diseases, such as mosquitoes spreading malaria. Other pest insects do not directly hurt people. Termites and some beetles eat wood and sometimes eat buildings, such as houses. Many insects eat agricultural products (plants meant for people to eat). Grasshoppers are one example of pest insects that eat plants in agriculture.
Many people think all insects are bad, but this is not true. Many insects help people. Some kinds of insects, such as bees, make food (honey) that people can eat. The larvae of some moths make silk, which people use to make clothing. In some parts of the world, people actually eat insects. Eating insects for food is called entomophagy.
Insects help people in other ways. Many bees and flies pollinate plants. This means the insects help the plants make seeds by moving pollen from one flower to another. Some good insects eat pest insects, such as lady beetles (or ladybirds or ladybugs) eating aphids. Many insects eat dead plants and animals. This is good because, if they did not eat all the dead things, there would be dead plants and animals everywhere.
People often use poisons called insecticides to kill pest insects. Insecticides do not always work. Sometimes the pest insects become resistant to the insecticides, which means the insecticides can not hurt them anymore. Both the Colorado potato beetle and the diamondback moth are insects that are resistant to many insecticides. Insecticides do not only kill pest insects; sometimes many helpful insects are killed too. When helpful insects are killed, such as those that eat pest insects, the pest insects may come back in larger numbers than before because they are not being eaten by helpful insects anymore.
(Simplified) Taxonomy.
This taxonomy lists some of the better known groups of insects.


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