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With over one million insect species on the planet, it was necessary to develop a classification system. Despite their large number, they are classified into only a few orders.

Insects make up the Phylum Arthropoda and the class Insecta. Insecta is divided into Apterygota, which are wingless, and Pterygota which have wings. These are further broken down into over one million insect species.

Most people refer to any small creature that scurries or flies away when disturbed as an insect. However, a knowledge of biology is required to recognize insects and to distinguish one from other invertebrate animals.



Insects are animals and are members of the phylum known as Arthropoda. Members of this phylum have segmented bodies, some or all of which have a pair of jointed limbs. An exoskeleton is a hardened cuticle that covers the body and limbs, with flexible membranes between the segments allowing movement.

Arthropoda is the largest animal phylum, accounting for at least 85 percent of all animal species. It includes true insects, crustaceans, and arachnids, with each group, referred to as a class.

Insect Family

Insects are the most numerous class of Arthropoda, with over one million distinct species described so far, with many more still to be discovered.

All adult insects share the following characteristics:

  • The division of the body into three regions—head, thorax, and abdomen.
  • The presence of one pair of antennae.
  • The presence of three pairs of legs on the thorax.
  • The majority of them have wings as well.

Larvae often differ significantly from adults and may not be immediately identifiable as insects. Most lack wings, their antennae are barely visible, and their legs may be absent, though some may have both true and false legs on the abdomen.

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Subclass of Insects

The class Insecta is divided into two subclasses: Apterygota are wingless insects, and Pterygota have wings. However, some wingless insects are classified as Pterygota because they are thought to have lost their wings during evolution.

Jumping bristletails, firebrats, and springtails comprise Apterygota. They are tiny and live in soil or moist crevices. The young resemble miniature versions of the adults, and adults continue to molt after sexual maturity.

Based on their life histories, the Pterygota are divided into two groups. The Exopterygota have young called nymphs that resemble adults with externally developed wings resembling pads on their thorax. However, they do not have a pupal or resting stage.

Endopterygota has larvae, grubs, or caterpillars, which are often quite different from adults. Their wings are not visible outside until they reach the pupal stage. It should be noted that no adult pterygote insect molts, apart from mayflies.

These groups are very useful in evolutionary studies. However, the next grouping—the order-includes insects that are related to one another, such as dragonflies, beetles, butterflies, and moths.



Exopterygote includes 15 orders of almost 130,000 species. Exo refers to the way their wings develop. The wings develop outside the body without going through a larval or pupal stage. Some species do, however, resemble a pupa, but this is not a true pupal stage.

Exopterygota includes many species and has lice, stick insects, termites, grasshoppers, and cockroaches.

The Orthoptera, one of the better-known orders of the Exopterygota, is limited to jumping species like grasshoppers and crickets, with enlarged hindlegs, straight forewings, and the ability to attract the opposite sex by rubbing their legs together.

The hemipteroid orders, which are also pterygotes, are clustered around the central order. Hemiptera (true bugs) all have mouthpart specialization, culminating in the bug’s sucking rostrum. Many Hemiptera resembles beetles, but they can be distinguished by their sucking rostrum and vines that are either roof-like (aphids and leaf-hoppers) or flat on the back with over-lapping membranous parts.

Plecoptera: Stoneflies

Embioptera: Webspinners

Zoraptera: Angel insects

Dermaptera: Earwigs

Orthoptera: Grasshoppers and crickets

Phasmatodea: Stick insects

Notoptera: Ice crawlers and gladiators

Blattodea: Cockroaches and termites

Mantodea: Mantids

Psocoptera: Booklice and barklice

Thysanoptera: Thrips

Phthiraptera: Lice

Hemiptera: True bugs


The Endopterygota group contains the majority of the most successful insects. Because of the evolution of their larval and pupal stages, larvae can now use and exploit food that even adults cant.

Beetles form the order Coleoptera and are a large group with chewing mouthparts and hard forewings that meet down their backs.

Diptera, also known as true flies, have only one pair of flying wings, with the hind pair converted to tiny structures known as balancers. These vibrate rapidly in flight, assisting them in control. Diptera have sucking mouthparts adapted for piercing vertebrates’ skin and sucking their blood.

Almost everyone has seen a member of the Lepidoptera order made up of butterflies and moths. Moths and butterflies have colored bodies contained within the layer of scales covering their wings and bodies. Their mouthparts have been modified to absorb nectar, and their larvae are caterpillars, with the pupal stage known as a chrysalis.

Hymenoptera is made up of bees, wasps, and ants that have incredibly complex biology and lifestyles. The mouthparts can be used for chewing, but in many forms, they are used to lap or suck. They have two pairs of wings, with the front and back of each side held together in flight by a row of tiny hooks and a small waist.

Hymenoptera: Sawflies, wasps

Raphidiopters: Snakeflies

Megaloptera: Alderflies and allies

Neuroptera: Lacewings and allies

Coleoptera: Beetles

Strepsistera: Twisted-wing parasites

Trichoptera: Caddisflies

Lepidoptera: Butterflies and moths

Diptera: Flies

Mecoptera: Scorpionflies


Each order is divided into families that all end in -idae and each family is further divided into several distinct groups known as genera. Each genus is then subdivided into species, which are the different types of animals.

Members of one species can interbreed and produce fertile offspring, whereas members of different species either do not interbreed or produce sterile offspring.

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