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Learn all you need to know about the most diverse group of animals on Earth - insects!
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All About Insects
Insects are the largest and most diverse group of arthropods. Approximately one million species of insects have been named, described and classified.

This represents more than half of all known organisms on Earth. Common insects include beetles, flies, bees, grasshoppers and butterflies.

The defining characteristics of insects include an exoskeleton, a body divided into three segments, three pairs of jointed legs, compound eyes and one pair of antennae.

In the life cycle of most insects, the young do not resemble their parents. As the young grow and mature, they undergo changes in body form – a process known as metamorphosis. As young insects grow, they usually go through a series of molts whereby they shed their exoskeleton and form a new one.

Let's look at the parts and function of the body parts of an insect by looking at a bee.

Head: The head of an insect holds its sense organs which include eyes and antennae. The head also contains the insect’s mouth parts which are adapted and suited to the types of food it eats.

Thorax: The center body part of insects is the thorax. It holds three pairs of legs and in mature, flying insects, also holds one or two pairs of wings.

Abdomen: The abdomen is located behind the thorax. At the rear of the abdomen is the anus, which is the rear opening of the digestive system where wastes are removed. In some insects, such as bees and wasps, the abdomen also contains a stinging organ.

Antennae: Antennae are sense organs usually located at the front of the head. They often contain smell receptors which allow insects to detect smells. In some insects, the antennae can also detect changes in humidity – the amount of water vapor in the air.

Compound Eyes: Most insects have compound eyes. Compound eyes consist of thousands of tiny light receptors that work together to enable insects to see.

Wings: Insects are the only arthropods with wings. Most insects have two pairs of wings. The outer wings are often used for protection and the inner wings used for flight.
Arthropods are the most diverse and numerous group of animals. They make up over 80 percent of all known species of animals on Earth. They live in all areas of the Earth – from the deep ocean to hot, dry deserts and moist tropical rainforests.

Common aquatic arthropods include crustaceans such as crabs, shrimp and lobsters. Terrestrial arthropods include insects, spiders, ticks and millipedes.

Arthropods have a hard outer body covering called an exoskeleton. Made of chitin, the exoskeleton supports and protects the animal’s body and can also help reduce water loss.

Arthropods have paired limbs on each side of their segmented bodies. Some arthropods have modified limbs in the form of claws or wings.

An exoskeleton does not bend easily. To move about, arthropods have many joints which allow them to bend parts of their bodies.

Without an internal skeleton to support their bodies, arthropods are usually small in size. Aquatic arthropods, such as crabs and lobsters, are often larger than land arthropods as they are able to use the surrounding water for support.

Arthropods have organs and body systems for digestion, breathing, circulation and reproduction. They also have a variety of different sense organs, such as eyes and antennae.

All arthropods have bilateral symmetry and reproduce by sexual reproduction.

Some arthropods have specialized internal structures that produce venom. The venom is a type of poison that is injected by a bite or sting into other animals. It can be used to kill prey or for protection against predators. Wasps, bees, spiders and scorpions are often venomous.

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