Insect Classification - Subclass Pterygota and Its Subdivisions

The subclass Pterygota includes most of the world’s insect species. The name comes from the Greek pteryx, which means “wings.” Insects in the subclass Pterygota have wings, or had wings once in their evolutionary history. Insects in this subclass are called pterygotes. The main identifying feature of pterygotes is the presence of veined wings on the mesothoracic (second) and metathoracic (third) segments. These insects also undergo metamorphosis, either simple or complete.

Scientists believe insects evolved the ability to fly during the Carboniferous period, over 300 million years ago. Insects beat vertebrates to the skies by some 230 million years (pterosaurs evolved the ability to fly about 70 million years ago).

Some insect groups that were once winged have since lost this ability to fly. Fleas, for example, are closely related to flies, and are believed to descend from winged ancestors. Although such insects no longer bear functional wings (or any wings at all, in some cases), they are still grouped in the subclass Pterygota due to their evolutionary history.

The subclass Pterygota is further divided into two superorders – the Exopterygota and the Endopterygota. These are described below.

Characteristics of the Superorder Exopterygota:

Insects in this group undergo a simple or incomplete metamorphosis. The life cycle includes just three stages – egg, nymph, and adult. During the nymph stage, gradual change occurs until the nymph resembles the adult. Only the adult stage has functional wings.

Major Orders in the Superorder Exopterygota:

A large number of familiar insects fall within the superorder Exopterygota. Most insect orders are classified within this subdivision, including:

• Order Ephemeroptera - mayflies
• Order Odonata - dragonflies and damselflies
• Order Orthoptera - crickets, grasshoppers and locusts
• Order Phasmida - stick and leaf insects
• Order Grylloblattodea - rock crawlers
• Order Mantophasmatodea - gladiators
• Order Dermaptera - earwigs
• Order Plecoptera - stoneflies
• Order Embiidina - webspinners
• Order Zoraptera - angel insects
• Order Isoptera - termites
• Order Mantodea - mantids
• Order Blattodea - cockroaches
• Order Hemiptera - true bugs
• Order Thysanoptera - thrips
• Order Psocoptera - barklice and booklice 
• Order Phthiraptera - biting and sucking lice

Characteristics of the Superorder Endopterygota:

These insects undergo a complete metamorphosis with four stages – egg, larva, pupa, and adult. The pupal stage is inactive (a rest period). When the adult emerges from the pupal stage, it has functional wings.

Orders in the Superorder Endopterygota:

The majority of the world's insects undergo complete metamorphosis, and are included in the superorder Endopterygota. The largest of these nine insect orders are:

• Order Coleoptera - beetles
• Order Neuroptera - nerve-winged insects
• Order Hymenoptera - ants, bees, and wasps
• Order Trichoptera - caddisflies
• Order Lepidoptera - butterflies and moths
• Order Siphonoptera - fleas
• Order Mecoptera - scorpion flies and hangingflies
• Order Strepsiptera - twisted=wing parasites
• Order Diptera - true flies

_Sources:

• _{"Pterygota. Winged insects."  Tree of Life Web Project. 2002. Version 01 January 2002 David R. Madden. Accessed online September 8, 2015.}
• _{Pterygota, pterygote. Bugguide.net. Accessed online September 8, 2015.}
• _{A Dictionary of Entomology, edited by Gordon Gordh, David Headric.}
• _{Borror and DeLong's Introduction to the Study of Insects, 7th edition, by Charles A. Triplehorn and Norman F. Johnson.}
• _{"Subclass pterygota," by John R. Meyer, Department of Entomology, North Carolina State University. Accessed online September 8, 2015.}