Insects are the most common animals on our planet. In fact there are more types of insects than all other animals combined—well over 1 million different known species of insects have been identified. Some experts estimate that there might be as many as 10 million.

Insects have existed for more than 300 million years, During the Pennsylvanian period in the Paleozoic Era, insects were so common that some scientists have called that era the “Age of Insects.” The rocks formed during this period were formed in a warm, humid environment with many swamps and forests, a perfect habitat for many forms of insects.

Insects have a wide range of sizes. Some stick insects have been found that are 36 centimeters (14 inches) long. Butterflies have been found with wing spans of 32 centimeters, or more than a foot across. Most insects are incredibly small. Many are less that 1 millimeter in length.

Insects are part of the phylum Arthropoda. Arthropods include crustaceans, arachnids (spiders, ticks, and others), millipedes, and centipedes. The arthropods are segmented animals with a chitinous exoskeleton. Chitin is a natural material similar to cellulose. When we see beetles and roaches, we can recognize their chitinous exoskeleton.

All insects have three body regions: the head, thorax, and abdomen. Insects have three pairs of legs, one on each segment of the thorax. Insects usually have two pairs of wings at the adult stage, however, some only have one pair. A few, such as springtails, lice, and flees, have no wings.

Insects are classified into different orders based mainly on wing structure, mouth parts, and type of metamorphosis (Table 10.1). Most entomologists recognize around 32 different orders of insects, some of which are not very common.

Insect Classifications

Common Name Taxonomic Name Example
Ants, bees, and wasps Hymenoptera Honeybee
Aphids, white flies, and cicadas Homoptera Cicada
Butterflies and moths Lepidoptera Monarch
Caddisflies Trichoptera Caddisflies
Dragons and damsels Odonata Dragonfly
Earwigs Dermaptera Earwigs
Fleas Siphonaptera Dog flea
True flies Diptera Housefly
Grasshoppers Orthoptera Common grasshopper
Lacewings, etc. Neuroptera Green lacewings
Mantids Ephemeroptera Praying mantis
Mayflies Mantidae Stream mayflies
Roaches Blattodea Cockroach
Scorpionflies Mecoptera Scorpionflies
Stick insects Phasmida Walking stick
Stoneflies Plecoptera Common stonefly
Termites Isoptera Powder-post termite
True bugs Hemiptera Milkweed bug