Introduction  Mouthparts  Development

Insect Orders

Other Arthropods
 Spiders, etc.

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There is an immense number of insect species on the planet. So many so that no one person can know all of them. Today there are more than one million insect species that have been named and described. Some scientists believe that there may be another 15 million yet to be discovered and assigned names. The class Insecta is large and diverse as well as important ecologically. When compared with other groups, the number of insect species is much larger than the number of Arachnids (about 50,000 species) or Crustaceans (about 40,000 species) and represents more than three quarters of all animal species.

The phylum Arthropoda contains several classes and includes the insects, spiders, crusteacea, and relatives. These animals have an exoskeleton and jointed legs.

Characteristics of Insects

The insects body is divided into three regions; the head, throax, and abdomen. Sometimes it may be difficult to see the division between the abdomen and thorax. Within each region there are several segments, 3 for the thorax, 11 or 12 for the abdomen, and 6 or 7 for the head. The abdomen contains many of the important organs including those for digestion, excretion, and reproduction. The legs and wings, when present, are attched to the thorax. The thorax also contains the muscles to power the legs and wings. The head has the eyes, antennae, and mouth.

Insects also have three pairs of jointed legs, one pair of antennae, compound eyes and up to two pairs of wings. In addition to the compound eyes, there may be several single-faceted simple eyes. Compound eyes have several dozen to several thousand independent receptors with their own facets (lens-like).

Many people often identify insects based on their general appearance. While that usually works well, many insects mimic the appearance of other insects. This can make identification more difficult when only using color or general appearance. In order to properly identify insects, we have learned to look at specific characteristics to avoid confusion. In this example a robber fly mimics the appearance of a bumble bee for protection.

Most animals recognize, or quickly learn, that bumble bees have a painful sting. Flies do not. By looking like the bumble bee, the robber fly is less likely to be bothered by other animals. Note how the 'hairiness' in similar as is the appearance of the wings. But the fly has only two wings while the bee has four. The bee has a pinched waist, while that of the fly is broader. The fly is in the picture to the left.

Here are 2 insects from Kentucky that look alike; the baldfaced hornet, a fiercely defensive wasp, and a flower fly.

The similarities in coloration are remarkable, but the characteristics are very different. For example, look at the antennae, the wasp's antennae are much longer. The flower fly also has a broadly attached waist while the hornet's is pinched. Although the wasp has four wings and the fly only two, it is difficult to see in these pictures.

The last pair of look alikes from Kentucky are a paper wasp and the grape root borer moth.

Not only do they look alike, but the grape root borer moth acts like the paper wasp, flying during the day (unusual for many moths) and appearing to search plants for prey. The moth is actually laying eggs, not hunting for caterpillars to feed its larvae. The size and coloration are remarkably similar, but other characteristics give away the mimic. The moth has a broadly attached waist and scaly wings. The wasp has the pinched waist and transparent wings.

To classify insects, that is, to begin grouping similar insects, we use specific characteristics. By looking at the type of mouthparts an insect has, the number and characteristics of the wings, and by knowing the type of metamorphosis it undergoes during development, we can group insects into orders. Examples of insect orders would be the beetles or the flies.

Common Orders of Insects

Now we will look at some of the common orders of insects that are found in and around the home and surrounding landscape. All of the photos were taken in Kentucky.We will group insects by the orders they belong to. You might not realize it, but you are already familiar with most of these insect orders. For example, beetles are one group called Coleoptera and flies are another group called Diptera. All together there are approximately 32 orders of insects, but we will look at only 10 of them. Rather than trying to memorize the individual insects within the orders, we will learn the common characteristics they share within their groups. Here are the groups we will study and the types of insects within those groups.

Order Orthoptera: Grasshoppers, crickets, cockroaches, walkingsticks, praying mantids (Most entomologists will split this into several different orders, but for our Master Gardener training we will group them together)

Order Dermaptera: Earwings

Order Thysanoptera: Thrips

Order Hemiptera: Stink bugs, plant bugs, assassin bugs

Order Homoptera: Cicadas, planthoppers, leafhoppers, whiteflies, mealybugs, aphids, scales

Order Coleoptera: Beetles

Order Neuroptera: Lacewings, dobsonflies, antlions, alderflies

Order Diptera: Flies, mosquitoes, gnats, midges

Order Lepidoptera: Moths and butterflies

Order Hymenoptera: Sawflies, wasps, ants, and bees

Other Arthropods: Spiders, ticks, mites, millipedes, centipedes, sowbugs, scorpions

Updated November 2005

Photo credits:  R. Bessin, Department of Entomology, University of Kentucky; montage created by P. Dillon, Department of Entomology, University of Kentucky

The teaching modules on this site were created by Ric Bessin;
web functionality was created and is maintained by Pat Dillon
Department of Entomology, University of Kentucky, S-225 Agricultural Science Ctr North, Lexington, KY USA  40546-0091.
Please send questions or suggestions to: rbessin@uky.edu OR pdillon@uky.edu