How to Identify Insects to Order

Part of making an insect collection is learning how to correctly classify the specimens. This is a very challenging assignment, because there are so many insects and so many of them look alike. Do not be discouraged if there are specimens that cannot be identified. Remember that even professional insect taxonomists (entomologists who identify and classify insects) cannot identify every species of insect. Some must specialize in working with one group and others with another group.
Classification, the grouping and naming of insects, is an ever-changing science. Insect specialists separate and combine groups of insects based largely upon their morphological similarities, some having more influence in a decision than others. As such, this process is somewhat subjective and, thus, dynamic. A student of entomology may find slight differences in classification schemes depending upon which reference or which entomologist they consult, and these may change over time.
Not all orders of insects are the same size. For example, more than one-third of the named species of insects (300,000) are in one single order, the Coleoptera (beetles). The next largest orders are Lepidoptera (butterflies and moths), with 150,000 species; and Hymenoptera (wasps and bees), with 125,000 species. The order Diptera (flies) includes about 20,000 species. These four orders, Coleoptera, Lepidoptera, Hymenoptera, and Diptera, comprise more than 80 percent of the named species of insects.
Approximately 92,000 named species of insects occur in the United States and Canada. It is not known how many of these species occur in any one state or in even a small area within a state. A list of insects in New York, published in 1928, included more than 15,000 species, but hundreds of species have been discovered there since that time. States such as California, Arizona, Texas, and Florida probably far exceed the Midwest and Northern states in the total number of species of insects.
Estimates of the number of species for three representative states and also for all of USA and Canada are provided as an indication of the number of species that insect collectors may expect to find (Table 1). A collector who can find one or more representatives of each of the 24 orders discussed in this book will have a very diverse collection, and in so doing will learn a great deal about insects and their habits.
Table 1. Estimated Number of Species | |||||
Order | North Carolina | New York | Indiana | USA & Canada | World Wide |
Collembola | 169 | 200 | 200 | 314 | 9000 |
Thysanura | 6 | 5 | 7 | 25 | 900 |
Ephemeroptera | 121 | 61 | 120 | 690 | 3100 |
Odonata | 148 | 159 | 150 | 425 | 5500 |
Dictyoptera | 23 | 15 | 20 | 101 | 5800 |
Orthoptera | 235 | 121 | 150 | 925 | 20000 |
Dermaptera | 7 | 4 | 5 | 18 | 2000 |
Isoptera | 5 | 1 | 5 | 41 | 2900 |
Plecoptera | 94 | 59 | 85 | 408 | 2000 |
Psocoptera | 37 | 38 | 30 | 150 | 4400 |
Mallophaga | 164 | 53 | 90 | 318 | 4000 |
Anoplura | 11 | 11 | 15 | 62 | 900 |
Thysanoptera | 64 | 71 | 150 | 600 | 5000 |
Hemiptera | 568 | 727 | 800 | 4600 | 40000 |
Homoptera | 759 | 864 | 900 | 6700 | 50000 |
Neuroptera | 68 | 61 | 65 | 338 | 6500 |
Megaloptera | 9 | 10 | 15 | 61 | 300 |
Coleoptera | 3336 | 4546 | 4424 | 30000 | 350000 |
Mecoptera | 27 | 20 | 20 | 89 | 600 |
Trichoptera | 161 | 174 | 210 | 980 | 11000 |
Lepidoptera | 1428 | 2439 | 2000 | 10100 | 150000 |
Diptera | 2595 | 3615 | 3600 | 17000 | 120000 |
Siphonaptera | 14 | 26 | 28 | 250 | 2500 |
Hymenoptera | 2463 | 2300 | 2800 | 17000 | 125000 |
With so many different insects, and with them occurring in so many different places, it is no wonder that assigning common names is difficult and sometimes confusing. For example, the common name "stink bug" may be given to one insect in one part of the country and to a completely different insect in another part of the country. To reduce this confusion, a list of accepted common names has been developed by the Entomological Association of America. This list (Common names of Insects and Related Organisms 1997) includes many, but not all, common names.
An average person seldom uses scientific names, but refers to insects by common names such as "beetle," "blister beetle," or even "black blister beetle." In this example, the common name "beetle" may refer to any of thousands of insects belonging to the order Coleoptera. "Blister beetle," on the other hand, is a common name for all members of the family Meloidae, a subset of the order Coleoptera. "Black blister beetle" is the common name for Epicauta pennsylvanica, a particular species of insect. So, even though common names are very important and widely used, not all of them refer to individual insects. That is why standardized scientific names are necessary, especially to professional entomologists and insect collectors.
All insects belong to the class INSECTA. Within this class many ORDERS of insects exist. This booklet describes how to classify the insects into one of 24 Orders. Within each order, many FAMILIES may exist. Within families, many GENERA occur and, likewise, within Genera, many SPECIES exist. A general understanding of the scientific nomenclature and rank order of associated names is important for collectors. For example, in the blister beetle illustration below, a collector should know that the basic nomenclature is as follows:

Order = Coleoptera
Family = Meloidae
Genus = Epicauta
Species = pennsylvanica
All specimens in an insect collection should be identified at some level. Amateur collectors gain a good knowledge of insects by first classifying them according to their order name. An order is a name applied to a large group of insects having similar characteristics. For example, all butterflies and moths belong to the order Lepidoptera; all beetles, regardless of size, shape, or color, belong to the order Coleoptera; all flies belong to the order Diptera, and so forth.
In this book we will discuss the 24 orders listed here. Make a checklist of the insect orders you collect and display; it's a valuable organizing tool.
For professional entomologists and those who have sufficient interest, orders of insects can be further broken down. Orders are broken down into families, the families into genera, and the genera into species. Professional entomologists generally study insects at the genus and species level. The first word of an insect's scientific name is the genus to which it belongs, and the second word is the species name.
The Pictorial Key to the Order of Adult Insects included in this book should help you classify specimens to the order level. Similar keys exist for families, genera, and species separation, but are beyond the scope of this book. This book, as well as most field guides, also provides common names of the more frequently collected insects.
An insect collection check list is provided here for field collecting the insects required in this text.
Color, size, and markings of an insect, together with written information as to where it was found (locality) and what it was doing (behavior) allow an experienced entomologist to identify insects quickly. However, it should be stressed that this is not always a clear-cut process. Beginning entomologists should become familiar with the use of the order keys to avoid misidentifying insects that look alike. In addition, expertise in working dichotomous keys is a foundation for more in-depth identification (to the family, genus, or species level). The following chart depicts the current most commonly recognized orders of insects. In this publication we describe 24 common orders of insects, most of which can readily be collected in every state. Additional orders such as Protura, Diplura, Zoraptera, and Embioptera are rare and seldom encountered even by the most experienced collectors.
A dichotomous key is a tool that allows the user to determine the identity of insects based primarily upon what the insect looks like (its morphology). A key consists of a series of choices that lead the user to the correct name of a given insect. "Dichotomous" means "divided into two parts." Therefore, dichotomous keys always give two choices in each step. In this book, we present a dichotomous key for the classification of adult insects into their proper orders.
Start at the beginning of the key, and as you study the insect in question, you will be given a set of two mutually exclusive choices. Depending upon the answer to the question, you will either learn the proper order of the insect or you will be directed to another set of questions.
Eventually your choices will lead you to the name of the insect order. Once an insect is identified to order, you can assume that much of the biology, distribution, and key behaviors of the insect in question, are similar to other insects in the order.
Experience in working through the keys will help tremendously. Sometimes particular specimens are difficult to classify, even with the key. On occasion, a rare specimen may not easily key out. Do not be discouraged. Consult with a person who is well trained in classification, or contact a professional entomologist to assist. Remember that the following key is designed for adult specimens only. It will not work for immature insects.
Download the PDF below!
Common Insect Orders
Brief descriptions of the orders follow. Order names are usually derived from a Greek or Latin word that describes the group. Most of the orders can be separated based on differences in wing morphology, thus learning the origin of the order name is very instructive and helpful in learning about the insects belonging to that order. Name derivations are provided in parentheses next to the order name. Common name of the order is also provided as it often reveals additional information about the biology or morphology of the group.
Note: Line drawings of several insects from each order are provided as examples of the order. All measurements given in this section are based on average body length (front of head to end of abdomen) of the species shown with the exception of the Lepidoptera (where measurements indicate average length of the forewing). Color photographs of representative insects in their adult form are provided at the end of this book and also are available via the Internet. Photos make for excellent review or study, and while they may not be as valuable as real specimens, they make for a handy reference collection or series for insect judging contests.
Collembola - springtails |
Collembolans are very small (less than 1/5-inch long), wingless insects with only six abdominal segments. Most have chewing mouthparts. These primitive insects develop without metamorphosis. Most species live outdoors in the soil or on decaying vegetation and are found under stones, in leaf litter, and in other damp places. Some commonly are found clustered on the sides of trees where sap is oozing; others collect in large numbers on still water. Occasionally collembolans can enter buildings through tiny openings in windows, doors and foundations cracks to become nuisance pests indoors. |
Thysanoptera - thrips |
![]() Bristletail Lepismatidae 3/8 in. |
Ephemeroptera - mayflies |
![]() Mayfly Ephemeridae 3/4 in. Adults commonly are found near streams, ponds, and lakes and are attracted to light. The nymphs or young mayflies live in water and may take from one to three years to develop. Mayflies are a very important food source for fish. Anglers often try to imitate mayflies when making fishing hooks, especially for fly fishermen. |
Odonata - dragonflies and damselflies |
![]() Damselfly Coenagrionidae 1 1/4 in. ![]() Dragonfly Libellulidae 1 3/4 in. The nymphs of Odonata are found in water, and adults usually are nearby. Both the adults and nymphs feed on other insects. Sometimes the nymphs also feed on small fish. Dragonflies are larger than damselflies and hold their wings horizontally, like an airplane, when at rest. Damselflies either tilt up their wings, like butterflies, or hold them next to their abdomens when at rest. |
Dictyoptera - cockroaches, praying mantids, and walkingsticks |
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![]() American cockroach Blattidae 1 3/8 in. |
![]() German cockroach Blattellidae 1/2 in. |
![]() Oriental cockroach (female) Blattidae 7/8 in. |
![]() Oriental cockroach (male) Blattidae 7/8 in. |
![]() Wood cockroach Blattellidae 1 in. |
![]() Praying mantid Mantidae 3 in. |
Orthoptera - grasshoppers, meadow grasshoppers, katydids and crickets |
![]() Grasshopper Acrididae 1 1/2 in. ![]() Camel cricket Gryllacrididae 5/8 in. |
![]() Cricket Gryllidae 7/8 in. |
![]() Tree cricket Gryllidae 3/4 in. |
![]() Mole cricket Gryllotalpidae 1 1/4 in. |
![]() Katydid Tettigoniidae 2 1/4 in. |
Dermaptera - earwigs |
![]() Earwig Forficulidae 1/2 in. These insects live outdoors and, for the most part, hide during the daytime under leaves and in cracks in the ground. They come out at night and sometimes are attracted to lights. They are considered nuisance pests. |
Isoptera - termites |
![]() Termite (Adult) Rhinotermitidae 1/8 in. ![]() Termite (Soldier) Rhinotermitidae 1/8 in. ![]() Termite (Worker) Rhinotermitidae 1/8 in. Termites sometimes are incorrectly called white ants, but they are very different from ants in both structure and metamorphosis. True ants, which belong to the order Hymenoptera, have an abdomen constricted (pinched in) just behind the thorax; termites do not. Termites are one of the few animals that feed on wood. They are found in logs, stumps, fence posts, or sometimes in the timbers of buildings. It is here that they become a significant urban structural pest. |
Plecoptera - stoneflies |
![]() Stonefly Perlidae 3/4 in. The growing stage (nymph) lives under stones in rapidly running streams. The adults usually are found resting on plants or trees or on stones near streams. |
Psocoptera - booklice and psocids |
![]() Booklouse Liposcelidae 1/16 in. Some of the wingless Psocoptera are called booklice and are found around old books and papers and in damp, dark rooms. They feed on molds, fungi, and pollen and may build up to very high nuisance populations if left unchecked. |
Mallophaga - chewing lice |
Chewing lice attack all kinds of wild and domesticated birds and many common mammals. The eggs are glued to the feathers or hair of the host. Chewing lice are most often collected directly from the host. Standard precautions must be taken when handling animals to prevent transmission of diseases to humans. |
Anoplura - sucking lice |
![]() Hog louse Haematopinidae 1/32 in. |
Thysanoptera - thrips |
![]() Thrips Thripidae 1/16 in. Thrips commonly are found on many plants, including gladiolas, sunflowers, onions, and greenhouse crops where they cause injury. A common species that annoys people lives on small grains and grasses and is called the "oats bug". |
Hemiptera - true bugs |
![]() Largid bug Largidae 3/8 in. ![]() Water boatman Corixidae 3/16 in. Most true bugs live on land, but some, such as the giant water bug and water striders, live in or on water. Usually, those that live on land feed on plant juices or are predators of other insects, but a few, such as the bed bug, are parasites of humans and other animals. |
![]() Stilt bug Berytidae 5/16 in. |
![]() Ambush bug Phymatidae 3/8 in. |
![]() Leaf-footed bug Coreidae 3/4 in. |
![]() Bed bug Cimicidae 3/16 in. |
![]() Squash bug Coreidae 7/16 in. |
![]() Negro bug Thyreocoridae 1/8 in. |
![]() Assassin bug Reduviidae 3/4 in. |
![]() Chinch bug Lygaeidae 1/8 in. |
![]() Garden fleahopper Miridae 1/8 in. |
![]() Water strider Gerridae 5/8 in. |
![]() Plant bug Miridae 1/16 in. |
![]() Stink bug Pentatomidae 5/8 in. |
![]() Seed bug Lygaeidae 3/8 in. |
![]() Milkweed bug Lygaeidae 7/16 in. |
![]() Lace bug Tingidae 1/8 in. |
![]() Harlequin cabbage bug Pentatomidae 3/8 in. |
![]() Backswimmer Notonecgtidae 1/2 in. |
![]() Giant water bug Blostomatidae 2 in. |
Homoptera - cicadas, leafhoppers, treehoppers, scale insects, aphids, spittlebugs, planthoppers, and mealybugs |
![]() Planthopper Acanaloniidae 1/4 in. ![]() Aphid Aphididae 1/8 in. Homopterans are a very diverse order. Winged forms include leafhoppers, cicadas (sometimes called locusts), spittlebugs, planthoppers, and treehoppers. The aphids (plant lice) include both winged and wingless forms. Scale insects are covered throughout most of their lives by a waxy scale. All Homopterans feed on plants and, due to their piercing sucking feeding behavior, are capable of transmitting several plant diseases. Many serious plant pests belong to this order. |
![]() Spittlebug Cercopidae 3/8 in. |
![]() Leafhopper Cicadellidae 1/8 in. |
![]() Planthopper Dictyopharidae 5/16 in. |
![]() Treehopper Membracidae 1/4 in. |
![]() Armored scale Diaspididae 1/32 in. (individual scales) |
![]() Mealybug Pseudococcidae 3/16 in. |
![]() Cicada Cicadidae 1 1/8 in. |
![]() Buffalo Treehopper Membracidae 3/8 in. |
Neuroptera - lacewings, mantispids, owlflies, snakeflies and antlions |
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Megaloptera - dobsonflies, fishflies, and alderflies |
![]() Dobsonfly Corydalidae 2 in. ![]() Alderfly Sialidae 1/2 in. Dobsonfly adults are found near streams but are often are attracted to lights. Adults are remarkable due to their size and the size and shape of their mandibles, especially pronounced in the male. The larvae are called hellgrammites. They live under stones in rapidly running streams and are prized by fishermen because they make excellent bait. Fishfly and alderfly larvae also are found in water but only reach approximately half the size of the hellgrammite, which attains a length of 3 inches. |
Coleoptera - beetles |
Beetles make up approximately 40% of all insect species. They are found almost everywhere. For example, whirligig beetles and diving beetles live in water, whereas cucumber beetles, Mexican bean beetles, and alfalfa weevils feed on vegetation. Plum curculio attack fruits; granary weevils feed in stored grains; and stag beetles live in stumps and decaying logs. Others, such as scavenger beetles, live on dead animals. Some Coleoptera, such as lady beetles and ground beetles, are beneficial, because they feed on injurious insects. Many beetles are very destructive agricultural pests. The stylopids are unusual beetles that are parasitic on other insects such as wasps. Some entomologists consider them a separate order called Strepsiptera. |
![]() Long-horned beetle Cerambycidae 5/8 in. |
![]() Click beetle Elateridae 1/2 in. |
![]() Spotted cucumber beetle Chrysomelidae 3/16 in. |
![]() Elm leaf beetle Chrysomelidae 1/4 in. |
![]() Tortoise beetle Chrysomelidae 3/16 in. |
![]() Carion beetle Silphidae 3/4 in. |
![]() Colorado potato beetle Chrysomelidae 3/8 in. |
![]() Spinach flea beetle Chrysomelidae 3/16 in. |
![]() Sap beetle Nitidulidae 1/4 in. |
![]() Rove beetle Staphylinidae 5/8 in. |
![]() Alfalfa beetle Curculionidae 1/8 in. |
![]() Metallic wood borer Buprestidae 5/8 in. |
![]() Cadelle Trogossitidae 5/16 in. |
![]() Soldier beetle Cantharridae 1/2 in. |
![]() Locust leaf miner Chrysomelidae 1/4 in. |
![]() Firefly Lampyridae 1/2 in. |
![]() Snout beetle Curculionidae 1/2 in. |
![]() June beetle Scarabaeidae 5/8 in. |
![]() Japanese beetle Scarabaeidae 3/8 in. |
![]() Rose chafer Scarabaeidae 3/8 in. |
![]() Mexican bean beetle Coccinellidae 1/4 in. |
![]() Lady beetle Coccinellidae 1/4 in. |
![]() Whirligig beetle Gyrinidae 1/2 in. |
![]() Larder beetle Dermestidae 3/8 in. |
![]() Tiger beetle Cicindelidae 1/2 in. |
![]() Ground beetle Carabidae 3/4 in. |
![]() Saw-toothed grain beetle Cucujidae 1/8 in. |
![]() Flour beetle Tenebrionidae 1/8 in. |
![]() Spider beetle Ptinidae 1/8 in. |
![]() Darkling beetle Tenebrionidae 3/8 in. |
![]() Net-winged beetle Lycidae 5/8 in. |
![]() Carpet beetle Dermestidae 1/16 in. |
Mecoptera - scorpionflies |
![]() Scorpionfly Panorpidae 3/8 in. These insects are found resting on plants that grow along the banks of streams and in damp woods. The larvae are caterpillar-like and live in damp soil. The adults feed on insects, usually dead ones, although certain species capture live prey. The adults are sometimes attracted to lights. |
Trichoptera - caddisflies |
![]() Caddisfly Hydropsychidae 1/2 in. Caddisfly larvae live in streams and ponds. Many are called rock-rollers, because they cover their bodies with portable cases made of small stones, and other materials webbed together with silk. This casemaking habit gives the order its common name, since the word caddis means "case." The adults are found near streams, ponds, or lakes in which the larvae live but may be attracted to lights in large numbers. Caddisfly larvae and adults are important food for fish. |
Lepidoptera - butterflies and moths | ||||||||||||||||||||||||||||||||||
Butterflies and moths have four wings that are covered with tiny scales. In a few species, such as female cankerworms, adults are wingless. Metamorphosis is complete. Adults possess siphoning mouthparts (mouthparts prolonged into a long, tongue-like organ). Larvae of moths and butterflies are called caterpillars and have chewing mouthparts. These are among the most injurious pests of plants. Note: All Lepidoptera measurements given with the figures are based on average forewing length (base of the wing at the body to the tip of the wing).
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Diptera - true flies |
![]() House fly Muscidae 1/4 in. ![]() Horse fly Tabanidae 7/8 in. |
![]() Syrphid fly Syrphidae 3/8 in. |
![]() Fruit fly Tephritidae 1/4 in. |
![]() Bee fly Bombyliidae 5/8 in. |
![]() Mosquito Culicidae 3/8 in. |
![]() Crane fly Tipulidae 1/2 in. |
![]() Vinegar fly Drosophilidae 1/16 in. |
![]() Robber fly Asilidae 7/8 in. |
![]() Deer fly Tabanidae 3/8 in. |
Siphonaptera - fleas |
![]() Flea Pulicidae 1/32 in. A good way to collect fleas from a dog or cat is to use a fine-toothed flea comb. Dusting pyrethrum powder on pets as they stand over a white cloth or paper or bathing with flea soap also may yield good collecting. Fleas drop off the animals and are picked up easily. |
Hymenoptera - bees, wasps, ants, sawflies, and hymenopterous parasites |
![]() Ant Formicidae 1/4 in. ![]() Honey bee Apidae 1/2 in. Many adult Hymenoptera can be found near flowers or other plant material where they come to feed. The larvae of ants, bees, and wasps are found in the nest or hive, but those of sawflies feed on plants and so are more exposed. Some species of wasps are parasitic on other insects and are valued as effective natural control agents. Many bees, including the honey bee, are highly beneficial as plant pollinators. |
![]() Bumble bee Apidae 7/8 in. |
![]() Yellow jacket Vespidae 5/8 in. |
![]() Horntail Siricidae 1 1/4 in. |
![]() Velvet ant Mutillidae 1/2 in. |
![]() Cicada killer wasp Sphecidae 1 3/8 in. |
![]() Mud dauber wasp Sphecidae 1 in. |
![]() Hornet Vespidae 3/4 in. |
![]() Ichneumon wasp Ichneumonidae 3/8 in. |