The class Insecta (also called Hexapoda) is divided into orders, which are classification divisions that can assist in identifying an insect. Classification is an important step in determining the economic status of an insect. Information that is common to an order includes the type of metamorphosis and structure of the mouthparts and wings.
Order information will help identify the diversity of the group- where they may be found, types of food eaten, and variation in general body structure. With order information and information on host plant or host animal affiliation (i.e., what an insect is feeding on), it is often possible to determine if the insect is one of the primary pests or beneficials in the United States. By consulting texts with information on order and host plant or host animal affiliation, specific identification can be made and management options can be considered.
There are differences in opinion on the number of orders that should be recognized and the names that should be applied to these groups. The classification system used here is that used by Borrer etal.
A list of economically important orders is given below:
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The common names(s) of the orders are placed beside the order name. For each order the following information is provided- order name, common name(s), approximate number of described species, type of metamorphosis, type of mouthparts, type of wings, body form, and habitat and economic importance.
i. Order Collembola (Springtails):
About 1,500 species known.
Metamorphosis- None
Mouthparts- Chewing
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Wings- None
Body Form:
About 1/32 to ¼ inch long, elongated to robust, most with furcula (a forked structure arising on the ventral surface of the abdomen used to propel the insect through the air).
Habitat and Economic Importance:
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Terrestrial; found in leaf litter, and under bark, fungi, and soil; feeds on decaying plant material, fungi, and bacteria. Selected species occasionally damage young, tender plants near the soil surface.
ii. Order Thysanura (Silverfish):
About 400 species known.
Metamorphosis- None
Mouthparts- Chewing
Wings: None
Body Form:
About 3/8 inch long or shorter, elongated and slightly flattened, two or three long tail-like appendages (cerci) at the end of the abdomen, body usually covered with scales.
Habitat and Economic Importance:
Terrestrial; found in leaf mold, humus, and buildings. They are decomposers; no major agricultural importance.
iii. Order Ephemeroptera (Mayflies):
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About 1,500 species known.
Metamorphosis- Simple
Mouthparts- Chewing in nymphs, vestigial in adults
Wings- One to two pairs, membranous with numerous veins, wings held together above body when at rest.
Body Form:
About ¼ to ¾ inch in length, two or three long tail-like appendages at the end of the abdomen, front wings usually triangular and larger than the hind wings for adults; nymphs are variable in form, usually with leaf-like or plumose gills along the side of the body.
Habitat and Economic Importance:
Adults are terrestrial, short-lived and do not feed; common around ponds, lakes, and streams. Nymphs are aquatic, and feed on algae and detritus. Important source of food for fish. No agricultural importance.
iv. Order Odonata (Dragonflies and damselflies):
About 5,000 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair, elongate, membranous with numerous veins, dragonfly wings held flat protruding out from body, damselfly wings held together above body when at rest.
Body Form:
Variable in adult, about ¾ to 5 inch, compound eyes are large and multi-faceted, abdomen is elongated. Nymphs are variable in form; gills are leaf-like at the end of the abdomen in damselflies or recessed in the body in dragonflies.
Habitat and Economic Importance:
Adults are terrestrial; common around ponds, lakes, and streams; feed on insects such as mosquitoes while in flight. Nymphs are aquatic; feed on other aquatic insects and small fish. These are the important source of food for fish. No agricultural importance.
v. Order Orthoptera (Grasshoppers and Crickets):
About 24,000 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair or none, front wings elongated and thickened with many veins, hind wings are membranous and folded underneath the front wings when not in flight. Wings may be reduced in length.
Body Form:
Variable, from less than 1 inch up to 4 inches in length, hind legs are modified into jumping organs, body is long and slender with paired tail-like appendages (cerci) extending from the end of the abdomen, antennae are conspicuous.
Habitat and Economic Importance:
Terrestrial, most are plant feeders, some cause economic damage to range and crop lands. Some feed primarily on noneconomically important plants or weedy species.
vi. Order Mantodea (Mantids):
About 1,500 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair, front wings elongate and thickened with many veins, hind wings are membranous and folded underneath the front wings when not in flight.
Body Form:
Variable, from less than I inch up to 4 inches in length, front legs are greatly modified into grasping organs, the first pail of the thorax is elongate giving the body the appearance of having along neck, body is long and slender with cerci extending from the end of the abdomen, antennae are apparent.
Habitat and Economic Importance:
Terrestrial, all species are predaceous, feeding on other insects. These are sold as biological control agents but unable to reduce pest species populations below an economic level because of slow generation turnover.
vii. Order Blattaria (Cockroaches):
About 1,500 species known:
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair, front wings thickened with many veins, hind wings are membranous and folded underneath the front wings when not in flight. Wings may be absent or reduced in length.
Body Form:
Variable, about ¼ to 1 inch in length, body is somewhat oval and flattened with cerci extending from the end of the abdomen, antennae are long.
Habitat and Economic Importance:
Terrestrial, cockroaches are primarily tropical but some are adapted to more temperate regions. They are scavengers and can feed, on various household items including stored products.
viii. Order Isoptera (Termites):
About 1,900 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair, front and hind wings equal in size or nearly so (in ants the front wing is longer than the hind wing). Only the reproductive caste has wings. They are shed at the end of the mating flight. Wings are held flat over the abdomen.
Body Form:
Variable, about 1/8 to 1 inch in length, soft-bodied and usually light-colored (the reproductive caste is darker than the other castes). Size and form differs among castes. In all castes, the abdomen is broadly-joined to the thorax (in ants the union is constricted). Antennae are moniliform or filiform. The reproductive caste is winged and the worker and soldier castes are not winged. The soldier caste usually has enlarged mandibles.
Habitat and Economic Importance:
Terrestrial, they are social insects dividing the labor of the colony into different castes. Some colonize in moist soil, whereas others colonize in dry habitats above ground. All are able to digest cellulose. Some are series pests of wooden structures. They are also important decomposers of woody plant material in natural systems.
ix. Order Dermaptera (Earwigs):
About 1,000 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- One or two pair, front wings are short, leathery and without veins. Hind wings (if present) are folded underneath the front wings. Wings are held flat over the abdomen.
Body Form:
About ¼ to ½ inch in length, soft bodied, elongate and somewhat flattened. Antennae are often long and moniliform. One pair of cerci is at the end of the abdomen. The cerci are conspicuous, and modified into pinching structures.
Habitat and Economic Importance:
Terrestrial, nocturnal. They feed on dead vegetable matter, occasionally feeding on tender parts of living plants (such as the silk of corn). Some are predaceous on other insects. They are important decomposers of plant material in natural systems.
x. Order Plecoptera (Stoneflies):
About 1,500 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair, membranous and multi-veined, wings folded flat over abdomen when at rest.
Body Form:
Adults are about 1/8 to 1 ½ inch in length, somewhat flattened, soft-bodied, antennae are long and slender, cerci present. Nymphs are elongate, somewhat flattened, and soft-bodied. Antennae and cerci are long. Gills are present on the thorax and bases of the legs.
Habitat and Economic Importance:
Adults are terrestrial, poor flyers, and are commonly found along shore lines. Nymphs are aquatic, often found underneath stones in streams; they are plant-feeders, feeding mainly on blue-green algae. They are an important food source for fish. They are not agriculturally important.
xi. Order Psocoptera (Psocids):
About 1,000 species known.
Metamorphosis- Simple
Mouthparts- Chewing
Wings- Two pair or none, membranous, wings held arched over abdomen when at rest.
Body Form:
Less than 1/8 inch in length, soft-bodied, generally has the appearance of lice (common names include bark and book lice).
Habitat and Economic Importance:
Terrestrial, decomposers of plant and animal matter. They also feed on algae, stored products, pollen, and molds.
xii. Order Plithiriaptera (Lice):
About 3,000 species known.
Metamorphosis- Simple
Mouthparts- Chewing (suborder: Mallophaga) or piercing- sucking (suborder: Anoplura).
Wings- None
Body Form:
Less than 1/8 inch in length, soft-bodied, and flattened. In chewing lice, the head is broad. In sucking lice, the head is narrow.
Habitat and Economic Importance:
Terrestrial, most chewing lice are ectoparasites of birds, but some feed on the skin of livestock. They feed on feathers, hair, and skin flakes. Sucking lice only feed on mammals. They are blood feeders and some transmit disease organisms. Lice are important to human (two species of sucking lice attack people) and animal health. Some chewing lice are serious pests of poultry and cattle and some sucking lice are serious pests of cattle.
xiii. Order Hemiptera (“true” bugs):
About 52,000 species known.
Metamorphosis- Simple
Mouthparts- Piercing-sucking, beak arises from the front of the head and usually extends back along the ventral side of the body.
Wings- Two pair, the basal portion of the front wing is thickened and leathery and the tip is membranous. The bind wing is membranous and is folded underneath the front wing when at rest. The wings, fold flat over the body.
Body Form:
Adults are variable, 1/32 to 2 inches in length. Antennae are apparent. The body is somewhat flattened. A small triangular region (scutellum) is visible at the mid-section of the body from a top view. Nymphs have the same body form as adults except the wings vary in length from barely visible buds to fully develop when matured to the adult stage. There are usually five nymphal instars.
Habitat and Economic Importance:
Terrestrial, some are semi- aquatic, all stages generally feed on the same food source. Most are plant feeders, feeding on leaves, stems, seeds, and fruit structures. Some are predaceous, feeding on insects and eggs of insects. A few species feed on the blood of humans and other animals. The semi- aquatic species (they are not true aquatics because they must take in air) dive in the water or skim the water surface.
xiv. Order Homoptera (Cicadas, hoppers, psyllids, white/lies, aphids, and scale insects):
About 32,000 species known.
Metamorphosis- Simple
Mouthparts- Piercing-sucking, beak arises from the back of the head and usually extends back along the ventral side of the body. In some adults the mouthparts are absent or reduced.
Wings- Usually two pair, or none, front wing is uniformly membranous or slightly thickened, hind wing is membranous and is folded underneath the front wing when at rest. The wings are arched over the body when at rest. In some species wingless forms occur. Sometimes winged and wingless forms occur in the same sex; in these species, formation of wings may be linked to host plant condition.
Body Form:
This is a highly variable group. Cicadas and hoppers- 1/8 to 1 inch in length, short antennae and bristle-like. Cicadas have membranous wings, hoppers have front wings somewhat thickened. Psyllids are less than 1/8 inch in length. They resemble cicadas in form. They have jumping legs and relatively long antennae.
Adults are winged. Whiteflies are about 1/16 inches in length. Adults are winged and resemble small white moths. A white dust covers the wings. The first instar nymphs are active crawlers, latter instars are sessile and resemble scales. Aphids- about 1/16 to ¼ inch in length.
Generally pear shaped with tubular protrusions (cornicles) at the end of the abdomen, generally long antennae. In some species, wingless forms occur, sometimes winged and wingless forms occur in the same sex. Eggs are produced, but in some species females can give birth to live young without mating.
Scale- variable, 1/16 to 1 inch in length. Females are wingless, legless, and sessile. Males have one pair of wings, a style-like process at the end of the abdomen, and resemble small gnats. The first instar nymphs are active crawlers, latter instars are sessile, wax or scale is secreted and covers the body when viewed from above.
Many species can reproduce asexually. Habitat and economic importance: terrestrial, they suck sap from stems, leaves, and roots of plants. Species may be specialized to feed on certain plant species and structures. Some are vectors of plant pathogens, some cause plant deformities called galls, and some cause leaf streaks.
xv. Order Thysanoptera (Thrips):
About 4,000 species known.
Metamorphosis- Simple
Mouthparts- Piercing-sucking
Wings- Two pair, slender and fringed with hair. They lay flat on the back at rest and may not be noticed. Wings may be absent in some species.
Body Form:
Adults are 1/32 to 1/8 inch in length and slender in form. Antennae are apparent but short. Asexual reproduction occurs in some species.
Habitat and Economic Importance:
Terrestrial, typically plant feeders, found on flower and fruiting heads and new growth. Some are vectors of plant disease and some are predaceous on other insects.
xvi. Order Neuroptera (Lacewings, snakeflies, alderflies, and others):
About 5,000 species known.
Metamorphosis- Complete
Mouthparts- Chewing
Wings Two pair, membranous and multi-veined. They lay arched over the back at rest.
Body Form:
Adults are variable, about 3/8 to 3 inches in length and slender in form, soft-bodied. Antennae are long and slender. Larvae are also soft-bodied, slender to stout in form. They may be very active. Larvae of aquatic species have processes extending lateral from the abdomen.
Habitat and Economic Importance:
Terrestrial and aquatic species. All species are predaceous as larvae. Adults may or may not feed. Generally feed on other insects. Lacewings mostly feed on aphids.
xvii. Order Coleoptera (Beetles):
About 265,000 species known.
Metamorphosis- Complete
Mouthparts- Chewing, adult weevils have reduced mouthparts retracted at the end of a snout.
Wings- Two pairs, the front wings are thickened, leathery or hard forming a protective shield as seen from above. The hind wings are membranous, usually longer than the front wings, but folded underneath the front wings when at rest. In some species, the wings are reduced.
Body Form:
Adults are variable, about 1/32 to 3 inches in length, hard-bodied. Antennae are variable in length (from short, not extending past the head, to longer than the length of the body) and form (from knoblike to slender). Larvae are also variable in size and form (slender to stout), generally soft-bodied.
Slender-bodied larvae with well-developed true legs tend to be active and likely search for their food (many scavengers, and predators). Stout-bodied larvae with weakly developed legs, or with legs absent, tend to be sessile or slow moving and likely feed on stationary food sources (many plant feeders).
Habitat and Economic Importance:
Mostly terrestrial and some aquatic species. Adults tend to be strong fliers and are the dispersal and reproductive stage of the insect. Feeding by adults may be common or limited, some feed on the same food source as the larvae. Larvae are highly variable. Some are plant feeders; foliage feeders, wood and stem borers, fruit feeders, root feeders, leaf miners.
Some species are scavengers feeding on stored products and gains, fungi, animal waste, dead plant and animal material. Some species are predators feeding on other insects. A few species are animal parasites. Some plant feeders are considered beneficial because they feed only on weedy plant species. Because of this diversity of feeding, this order consists of many beneficial and destructive insects.
xviii. Order Siphonaptera (Fleas):
About 1,100 species known.
Metamorphosis- Complete
Mouthparts- Sucking
Wings- None
Body Form:
Adults are less than 1/8 inch in length, body is laterally flattened with stout hairs arising from the body, all tending to point toward the end of the body. Most species have long well-developed legs enlarged for jumping. Larvae have a simple tubular body with hairs tending to point toward the end of the body. The body is whitish and has a pair of blunt appendages at the end of the body. There are no legs.
Habitat and Economic Importance:
Terrestrial, adults of both sexes feed on the blood of their hosts. A wide range of hosts are attacked, but a given species usually has a limited host range. Larvae are active but usually not seen because they are found in the nesting material of their host. They feed on animal waste, dried blood, and possibly decaying plant material that is used to construct the nest. Some species are vectors of animal diseases.
xix. Order Diptera (“True” flies):
About 85,000 species known.
Metamorphosis- Complete
Mouthparts- Sucking, various modifications occur resulting in piercing-sucking, sponging-sucking, and lapping-sucking functions. In some species, the mouthparts are highly reduced and nonfunctional. Mouthparts of some larvae are chewing.
Wings- One pair, second pair is modified into small knobby structures called halteres. The fore wings are membranous, often with multiple veins.
Body Form:
Adults are variable, < 1/8 inch to ¾ inch in length, soft-bodied. Antennae short and stout to long and slender. The union of the abdomen and thorax is broad, not constricted as in most bees and wasps. Larvae are legless and generally maggot-like.
Two General Groups Occur, are as follows:
1) Primitive families have a well-developed head capsule and strong chewing mandibles,
2) Higher families have the head reduced, a head capsule may or may not be apparent, and mouthparts have been modified into hooks that can be retracted into the body.
Habitat and Economic Importance:
Terrestrial, many larvae can be termed semi-aquatic because they feed in very moist habitats. Adults are found in a wide range of habitats. Some species feed on blood, other species feed on decaying organic matter or nectaries, a few species do not feed.
Some are animal and plant disease vectors. Larvae are slow moving and feed on a variety of food sources, including decaying animal and plant material, plant roots, stems (stem borers), and leaves (leafminers), and organic material in semiaquatic habitats. Some species are beneficial, feeding on other insects as predators or parasites. Some species are endoparasites of mammals.
xx. Order Trichoptera (Caddisflies):
About 4,500 species known.
Metamorphosis- Complete
Mouthparts- Chewing, mandibles are reduced in the adult.
Wings- Two pair, membranous wings, multi-veined, and hairy. They are usually arched over the abdomen when at rest.
Body Form:
Adults are 1 ⅙ to 1 ½ inch in length, soft-bodied, similar to moths in general appearance. Antennae tend to be long and slender. Larvae have caterpillar-like forms (eruciform). A well- developed head capsule and thoracic legs. A pair of hooked structures occur at the end of the abdomen. In some species the larvae are housed in a case made of debris by the larvae.
Habitat and Economic Importance:
Terrestrial as adults, larvae are aquatic. Adults are weak flyers, found near the edge of water of flowing streams. Larvae are either free-living species or species that are housed in cases made by the larvae. Some species are found attached to rocks in flowing streams, others are found in ponds or lakes. They are an important food source for fish and other aquatic organisms. No agricultural importance.
xxi. Order Lepidoptera (Butterflies and Moths):
About 105,000 species known.
Metamorphosis- Complete
Mouthparts- Chewing in larvae, siphoning in adults.
Wings- Two pair, membranous wings with scales. Butterflies hold their wings arched over the abdomen when at rest. Moths usually hold their wings flat over the abdomen when at rest.
Body Form:
Adults are variable, ¼ to 4 inches in length, soft- bodied. Antennae tend to be long and slender. Larvae are eruciform, with well-developed head capsule, thoracic legs, and up to five pair of false fleshy legs (prolegs) along the underside of the abdomen. Usually at the bottom of the prolegs are small hooks (crochets). Some species, mostly leaf miners, do not have legs. Various forms of processes (hairs, spines) may extend from the body wall.
Habitat and Economic Importance:
Terrestrial, a few species are aquatic as larvae. Adults feed on the nectaries of plants. Larvae most often feed on plants. Feeding habits vary greatly- leaf miners, stem borers, tree borers, foliage feeders, fruit feeders, and fruit borers, etc. Some species feed on cloth fiber and stored products and grain. Some plant feeders can be considered beneficial because they feed primarily on weedy plant species.
xxii. Order Hymenoptera: (Sawflies, wasps, ants, and bees):
About 110,000 species known.
Metamorphosis- Complete
Mouthparts- Chewing, in adult bees and other species the mouthparts are modified into a tongue-like structure through which liquid is taken.
Wings- Two pair, or absent, membranous. The hind wing is smaller than the front wing. Venation is moderate to highly reduce. In some species, wingless forms occur.
Body Form:
Highly variable group, antennae are generally long, ovipositor of the female is usually well developed or modified into a stinger. Adult sawflies are 3/8 to 1 ½ inches in length, union of the thorax and abdomen is broad. Larvae are eruciform with a well-developed head capsule.
Six to eight, usually eight, pair of prolegs without crochets. Parasitic wasp adults are variable, < ¼ to > 1 inch in length. Membranous wings have few veins. Union of the thorax and abdomen is constricted. Larvae are grub-like, often concealed in the body cavity of the host insect or other arthropod.
Ant adults are < ¼ to ½ inch in length, elbowed antennae, union of the thorax and abdomen is constricted (these features distinguish adult ants from adult termites). Wings are present during the mating flight and are shed afterward. Separate non-reproductive caste, the workers, do not have wings (ants are social insects with queen, male, and worker castes).
Larvae are grub-like, whitish in color. They are secluded in the ant colony. Adult bees and stinging wasps are ½ to 1 inch in length. Union of the thorax and abdomen is constricted. The ovipositor is modified into a stinging organ. Some species are social and have separate castes. The queen is larger than the other castes (such as honey bees) and is responsible for reproduction in the colony. Larvae are grub-like, concealed within the nest or colony.
Habitat and Economic Importance terrestrial, great variety in habitats. Larvae of sawflies are external feeders on foliage, some species are wood borers. Parasitic wasps are parasites of insects and some other arthropods. Larvae feed internally or externally on the host. A few species of chalcid larvae feed inside seeds and stems, possibly causing gall formation.
All ant species are social with three castes. Ants forage from a central colony. One queen per colony. Most species nest in the ground, but some nest in cavities in plants. The food sources of the various species include animal flesh, plants, fungi, sap, nectar, and honeydew.
Stinging wasps use their stinger to paralyze their prey, which is used as a food source for larvae that are tended, to varying degrees, in a nest. Bees use their stinger as protection. They forage on flowers to obtain nectar and pollen. The pollen is provided to larvae in a nest or colony. Overall, most species of Hymenoptera are beneficial functioning as parasites and pollinators.