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When you have finished this page, try the Insects Quiz:

Insects are part of a bigger animal group called arthropods. The word Arthropod literally means jointed limbs. The arthropods are the first animal group to have jointed legs.

Insects have certain characteristics. They have six legs. They have three body parts, a head, a thorax and an abdomen. They have wings. They are by far the largest animal group. They also have an outer or exoskeleton made of a substance called chitin..

There are over 700, 000 species of insects. While they are relatively small in size compared to many animal groups, they are well adapted to their environments. Most insects live on land.

All insects grow from eggs. They go through various stages until they reach adulthood. This transformation through these stages is called metamorphosis. Insects undergo either complete or incomplete metamorphosis.

The dragonfly, termite, grasshopper and true bug undergo incomplete metamorphosis. In this process there are three stages called egg, nymph and adult. When the nymph hatches from the egg, it looks like the adult insect except it is smaller, has no wings and cannot reproduce yet. As the nymph grows it outgrows its outside skeleton and it is shed. It then regrows a new one. This happens several times before it finally becomes an adult.

Insects like the butterfly, bee, ant, beetle and fly undergo complete metamorphosis. This involves four stages: egg, larvae, pupae and adult. The larvae looks like a worm and hatches from the egg. As it grows, it also sheds it skin. It then grows into a pupa. While the pupa doesn't move around like the larva, it does eventually at this stage change from an immature form to adult form.

There is another group within the arthropods called the arachnids. The arachnids are spiders, scorpions, etc. The annelids are similar to insects. However, they have eight legs. Their wings are quite different from those of the insects.

Since this group is so very big, there are links below to pages on some of the biggest groups within the arthropods:



System Type
Insect's System
Muscular-Skeletal A insect has an outer skeleton. The skeleton has three layers: the outer It has three pairs of legs and one or two pairs of wings. The legs are segmented and depending on the insect, may have a clawlike structure on the last segment. Insect muscles are connected to their outside skeleton and are generally gray.
Digestion A insect has different kinds of mouths depending on the species. Some can chew, some can suck objects. The digestive system is a tube that goes from the mouth to the anus. It is divided into several sections, the foregut, the midgut and the hindgut.
Nervous A insect has antennae that can be used to detect odors or to touch objects. Insects have two sets of eyes: simple eyes and compound eyes. The simple eyes have cornea, retina, pigment cells, etc.. There is a brain and nerve cells.
Circulation A insect has a circulatory system that carries food, but not oxygen throughout its body. Since it does not carry oxygen, insect blood is green, not red like mammal blood. The insect heart is a simple tube running along their backs.
Respiration A insect breathes through thoracic and abdominal spiracles. Since the insect has no lungs, the spiracles go throughout the insect body to give gases. Thus the insect bodies are relatively small.
Reproduction A insect generally reproduces sexually, although not always. The female genitals are external or outside the body. The eggs are held in an ovipositor. The females' internal sexual organs are ovaries and the males' are testes that produce sperm.
Excretion A insect passes food through its digestive system and the insect feces pass out of its anus from the hindgut.
Symmetry A insect has bilateral symmetry.
Appearance The insect is generally relatively small. It can be many different colors depending on the species.



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