Insects and mites belong to a large group of animals known as arthropods. Several characteristics differentiate insects from other arthropods. The body is segmented, and the segments are grouped into three sections: head, thorax and abdomen. The eyes, antennae and mouthparts are on the head, and the legs and wings are on the thorax.
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In contrast, mites have no antennae, and adult forms usually have four pairs of legs. The head and thorax are smaller and fused in mites. The abdomen is relatively large and bulbous and is not distinctly segmented.


An insect's skeleton is on the outside of its body and is called an exoskeleton. It serves as a support for muscles and internal organs as well as a covering. The body wall of an insect has three layers. The outer layer is cuticle containing chitin, proteins and often pigments. This is secreted by a cellular layer beneath it called the epidermis. The inner layer is called the basement membrane.



The type of mouthparts an insect has determines how it feeds and what sort of damage it does. There are two general types: chewing and sucking. Insects with sucking mouthparts suck liquid food through an elongated beak. Insects with chewing mouthparts tear off pieces of host tissue and ingest it.
 

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Growth progresses through successive stages. Females lay eggs, which hatch into an immature stage. After passing through a series of immature stages, the insect emerges as an adult. Adults mate and the cycle begins again.



Most insects start as eggs, which vary in size, shape and color. They can be deposited singly or in compact masses but are usually protected in some way. They may be laid in the ground or in or on plant tissue. Eggs left exposed are often protected from the elements and natural enemies by a coating.



Eggs may be round, oval, barrel shaped, disk shaped or suspended on long stalks. The tough outer surface protects the embryo and prevents water loss.



The first immature stage of the insect hatches from the egg. As the insect's rigid exoskeleton cannot expand much, it must be shed and replaced with a larger one as the insect grows. This process is called molting. The life stage between each molt is called an instar.



Molting is