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INSECTS

INSECTS appear in mythology not only as the gods, often as the creators of the world, but also as messengers to the gods. They serve sometimes as the agents of creation and frequently function as symbols of the human soul. Moreover, some insects, such as cicadas, beetles, and scarabs, often symbolize rebirth, resurrection, or eternal life.

According to the Lengua, a South American tribe of the Gran Chaco, a god in the shape of a huge beetle created the world and peopled it with mighty spirits. He holds aloof, however, from his creation and is not invoked in prayer. The butterfly is often worshiped as a god, sometimes as the creator. In Madagascar and among the Naga of Manipur, some trace their ancestry to a butterfly. According to the Pima of North America, at the time of beginning the creator, Chiowotmahki, assumed the form of a butterfly and flew over the world until he found a suitable place for humankind.

It is, however, the spider that plays a prominent part in the myths of North American Indians; it appears as the creator (e.g., among the Sia Pueblo Indians) or culture hero, or at least as the trickster (among the Dakota Indians). The Jicarilla Apache believe that at the time of beginning, when creatures lived in the underworld, the spider spun a web in the hole leading up to the earth and, together with the fly, came up on it before the people emerged. The spider and the fly were told by the Holy Ones to make a web and extend it to the sky in order to bring down the sun. According to the Navajo, Spider Man and Spider Woman are supernatural beings who instructed their mythical ancestors in the art of weaving and established the four warnings of death. The spider is also conspicuous in West African myths. In some myths, he is creator of the world; in others, he plays the role of culture hero, as in the stories in which he steals the sun. However, his usual role is that of a crafty and cunning trickster who prospers by his wits.

In Hindu mythology, ants are compared to a series of Indras. One day Indra in his palace receives a visit from a boy dressed in rags, who is Viu in disguise. While the boy speaks of the innumerable Indras who people the innumerable universes, a procession of ants appears in the great hall of the palace. Noticing them, the boy suddenly stops and bursts into laughter. "What are you laughing at?" asks Indra. The boy replies, "I saw the ants, O Indra, filing in long parade. Each was once an Indra. Like you, by virtue of pious deeds each one ascended to the rank of a king of the gods. But now, through many rebirths, each has become again an ant. This army is an army of former Indras."

In West Africa, ants are often viewed as the high god's messengers. In the Romanian creation myth, the bee serves as God's messenger. It also helps God to complete his creation with advice that it overhears from the hedgehog. Although the angry hedgehog puts a curse on it, condemning it to eat only ordure, God blesses the bee so that the filth it eats may become honey.

The bee is still an important symbol in Islam. The Qurʾān explicitly mentions it as a model of an "inspired" animal, and both Muammad and, even more, ʿAlī are connected in folklore with the pious and useful bee. Honey becomes sweet, it is said, because the bees hum blessings for the Prophet as they go about their work.

In some earth-diver myths, which speak of the origin of the earth from the primordial waters, insects serve as agents of creation. According to the Garo of Assam, the goddess Nosta-Nōpantu was to carry out the work of creation on behalf of the god Tattaro-Robuga. To get a particle of soil from the bottom of the primeval ocean, she sent in turn a large crab, a small crab, and a dung beetle. Only the dung beetle succeeded in bringing up a little clay, and from this Nosta-Nōpantu formed the earth. The Semang Negritos of the Malay Peninsula (such as the Menik Kaien, Kintak Bong, and Kenta tribes) similarly believe that the earth was brought up from the primeval ocean by a dung beetle, although in this version the insect seems to have dived on its own initiative. Among the Shan of Burma, the divers are ants. In North America, too, insects are known as earth divers among the Cherokee. In contrast to earth-diver myths are stories that speak of the celestial origin of the earthas in the Indonesian and Micronesian cosmogoniesand in these myths, too, insects play an important role. The Toba and the Batak of Sumatra, for example, have preserved the tradition that a swallow and a large dung beetle brought down a handful of earth from the sky.

While bees, ants, and dragonflies often symbolize the souls of the dead, the image of the butterfly as the human soul is widely diffused in Europe, Asia, and the Pacific islands. The early Greeks sometimes depicted the soul as a diminutive person with butterfly wings, and later as a butterfly. A similar belief was shared by the Romans. The Maori of New Zealand believe that the soul returns to earth after death as a butterfly, and in the Solomon Islands a dying person, who has a choice as to what he will become at death, often chooses to become a butterfly. In Japan, the motif has been incorporated into nō dramas, and in the world of Islam, it is one of the favorite images of Sufism: The moth that immolates itself in the candle flame is the soul losing itself in the divine fire.

The cicada, on account of its metamorphosis, was well known in ancient China as a symbol of rebirth or renewal of life. According to the Arawak of Guyana, at the time of beginning the creator came down to earth to see how humankind was getting along. But humans were so wicked that they tried to kill him; so he deprived them of eternal life and bestowed it instead on animals that renew their skin, such as serpents, lizards, and beetles. In ancient Egypt the scarab, a beetle of the Mediterranean region, was identified with the sun god Khepri and thus became a symbol both of the force that rolled the sun across the heavens and of the rising sun, self-generated. Scarab amulets made of green stone set in gold were placed over the heart of the dead during the funeral ceremony as a sign that just as the sun was reborn, so would the soul of the deceased be born again.

Insects are not always viewed as beneficent creatures. According to Northwest Coast Indians such as the Tlingit, the Haida, and the Tsimshian, mosquitoes are pests that originated from the ashes of an ogre's burned body. The same motif is found among the Ainu and in southern China. In Japanese mythology, spiders appear as a symbol of the evil forces that were subjugated by the heavenly gods before the imperial dynastyand with it, Japanwas established.

See Also

Tricksters.

Bibliography

On insects playing a role in cosmogonic myths, see Mircea Eliade's Zalmoxis, the Vanishing God: Comparative Studies in the Religions and Folklore of Dacia and Eastern Europe (Chicago, 1972), pp. 76130. See also Charles H. Long's Alpha: The Myths of Creation (New York, 1963), pp. 44ff. There is a fine study of scarab symbolism in the Greco-Roman world in Fish, Bread, and Wine, volume 5 of Erwin R. Goodenough's Jewish Symbols in the Greco-Roman Period (New York, 1956), pp. 172ff. Schuyler Cammann discusses the symbolism of the cicada in his very useful essay "Types of Symbols in Chinese Art," in Studies in Chinese Thought, edited by Arthur F. Wright (Chicago, 1953). On the origin of mosquitoes, see Gudmund Hatt's Asiatic Influences in American Folklore (Copenhagen, 1949), pp. 8990. On the Islamic symbolism of insects, there is an admirable study in Annemarie Schimmel's The Triumphal Sun: A Study of the Works of Jalaloddin Rumi, rev. ed. (London, 1980), pp. 108ff.

New Sources

Cherry, R. H. "Insects in the Mythology of Native Americans." Entomology 39 (1993): 1621.

Gosling, David L. Religion and Ecology in India and Southeast Asia. New York, 2003.

Hoyt, Erich. The Earth Dwellers: Adventures in the Land of Ants. New York, 1996.

Hoyt, Erich, and Ted Schulz. Insect Lives: Stories of Mystery and Romance from a Hidden World. New York, 1999.

Lauck, Joanne Elizabeth. The Voice of the Infinite in the Small: Re-Visioning the Insect-Human Connection. Boston, 2002.

Manabu Waida (1987)

Revised Bibliography

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Insect

Insects are a class of arthropods . Like other arthropods, they have exoskeletons made from the carbohydrate chitin , segmented bodies, and jointed appendages . Insects are distinguished by having three major body segments (head, thorax, and abdomen), with three pairs of legs attached to the thorax. Ancestral head appendages have been modified to form antennae and mouth parts, while abdominal appendages are either absent or modified to aid in reproduction. Most insects possess wings as adults, also attached to the thorax.

Sensory Systems

The insect head bears a single pair of compound eyes, composed of many individual units, called ommatidia, each of which senses a small portion of the visual field. Hunting insects such as the dragonfly may have thousands of ommatidia per eye, while others, such as ants, have many fewer. A single pair of antennae serves as chemical sensors to help find food or mates. In many species, including the tobacco hornworm moth, the female releases airborne chemicals called pheromones that attract the male. The highly branched antennae of the male moth can detect the molecules of the female pheromone, and can track the scent to find the female over very long distances. Chemoreceptors are also located on the feet, allowing an insect to taste its food as it walks across a leaf or a table. The numerous hairs covering the insect body are linked to mechanoreceptors, which aid its sense of touch. Some mechanoreceptors can sense changes in air pressure, useful for flying or evading a swooping predator. Receptors for carbon dioxide, water, and temperature also exist.

Ingestion, Digestion, and Excretion

Insect mouth parts vary tremendously in their shapes, reflecting adaptations to a wide variety of feeding habits. Mosquitoes, for instance, have a long hypodermic needlelike stylet, perfect for piercing skin to suck blood. Butterflies and moths, among others, have a very long, flexible strawlike mouth part, the proboscis, which they unfold to sip nectar from the base of flowers. Houseflies have a spongy tonguelike labrum for sopping up a variety of foods. Grasshoppers and beetles have small, sharp mouth parts adapted for chewing. The insect gut is divided into three regions, with most digestion occurring in the midgut. Suspended into the midgut are the Malpighian tubules, which filter nitrogenous waste from the blood and deposit it as crystals within the gut, avoiding the water loss that urine formation would entail. In termites, the hindgut houses a complex group of protists and bacteria that digest wood.

Legs and Wings

Insect legs are used for walking and climbing. In some predatory species such as the praying mantis, the front pair of legs has been modified for capturing prey, with barbed surfaces that hold other insects tightly. Almost all insects have wings, although a few primitive forms do not. In the ants, only the reproductive members of the colony have wings, which they shed after their "nuptial flight," in which they mate with members of the opposite sex.

Respiration and Circulation

Insects do not have lungs, but instead employ a highly branched network of internal tubes, called tracheae, to deliver oxygen to the tissues. Tracheae connect with the atmosphere through openings in the exoskeleton called spiracles. Insect circulatory systems transport nutrients and wastes in a fluid called hemolymph, which is pumped into and out of internal chambers surrounding the organs, an arrangement called an open circulatory system.

Reproduction and Development

Most insects reproduce sexually, although the aphids are a notable exception. Aphids reproduce by parthenogenesis, in which the egg develops into a new organism without fertilization . In honey bees and some other social insects, only one female per colony reproduces, and males are haploid , whereas females are diploid , a system called haplodiploidy. The queen produces new (diploid) females (workers, soldiers, and future queens) from fertilized eggs. Males are produced from eggs that are not fertilized, and thus males are haploid.

Insects vary in their degree of metamorphosis during development. Butterflies, beetles, and flies, for example, undergo complete metamorphosis, in which the egg hatches into a feeding larva, which then pupates. Within the pupa, the larval tissues dissolve and rearrange into the adult form. In contrast, grasshoppers, cockroaches, and cicadas undergo incomplete metamorphosis, emerging from the egg as a miniature adult, but minus the wings and genitals. To grow, all insects must molt, or shed their exoskeleton, which then reforms around the larger individual.

Metamorphosis often allows juvenile and adult individuals of the same species to avoid competition for food. Larval moths feed voraciously and can be significant agricultural pests, while adult moths either don't feed or consume only nectar.

Diversity

Insects are the most diverse of all groups of organisms, with over 800,000 species named and many thousands, probably millions, yet to be discovered. Insect diversity may be linked to their close association with the angiosperms (flowering plants). The Coleoptera (beetles) are the most diverse of all insect orders, with at least 350,000 species, representing one fourth of all known animal species. (Asked what could be inferred about the work of the Creator from a study of His works, British scientist J. B. S. Haldane is reported to have quipped, "an inordinate fondness for beetles.") The evolutionary reasons for the mind-boggling diversity of this single order are not clear. Other major orders of insects include the Diptera (flies), Hymenoptera (bees and wasps), Hemiptera (true bugs), and Lepidoptera (moths and butterflies). Note that each name describes the wing (ptera means "wing"). For instance, Diptera means "two wings," referring to the presence of only one wing pair in this order. In the Coleoptera ("sheath wings"), the first pair of wings is modified into a hard covering for the rear pair, which is easily observed in a lady beetle, for instance.

see also Angiosperms; Arachnid; Arthropod; Biodiversity; Osmoregulation; Physiological Ecology; Plant Pathogens and Pests; Symbiosis

Richard Robinson

Bibliography

Berenbaum, May. Bugs in the System. New York: Addison-Wesley, 1995.

Daly, H. V., J. T. Doyen, and A. H. Purcell. Introduction to Insect Biology and Diversity. New York: Oxford University Press, 1998.

Evans, Arthur V., and Charles L. Bellamy. An Inordinate Fondness for Beetles. New York: Henry Holt & Company, 1996.

Fabre, Jean Henri. Fabre's Book of Insects. Mineola, NY: Dover Publications, 1998.

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Insects

Insects are invertebrates in the class Insecta, which contains 28 living orders. The animals that make up this class have a number of distinctive features. Their adult bodies are typically divided into three parts, known as the head, thorax, and abdomen. In addition, they have three pairs of segmented legs attached to the thorax and one pair of antennae. Members of the subclass Pterygota have two pairs of wings as adults. By contrast, some relatively primitive members of the subclass Apterygota are wingless.

Taxonomists (scientists who classify organisms) have recognized more than one million species of insects, more than any other group of organisms. In addition, scientists believe that tens of millions of species of insects remain undiscovered. Currently, scientists estimate that as many as 30 million species of insects inhabit Earth; most of these are thought to be beetles. In fact, all of the insect orders are poorly known. Most of the undiscovered species of insects occur in tropical rain forests, especially in the upper parts of the forest known as the canopy.

Globally, the insects exploit a remarkable diversity of habitats. They are ecologically important as herbivores (plant-eaters), predators (meateaters who hunt their prey), parasites (who feed on living organisms), and scavengers (who feed on dead organisms). As a result of these attributes, insects are considered to be one of the most successful group of organisms on Earth, if not the most successful.

True Bugs

To a biologist, the term bug has a very special meaning. It does not refer to just any insect, as it may when nonscientists use the term. True bugs are members of the order Hemiptera. The order consists of about 35,000 widely different species. Examples of terrestrial (land-living) bugs living in North America are lice, aphids, bedbugs, stink bugs, plant and leaf bugs, assassin bugs, ambush bugs, seed bugs, lace bugs, and squash bugs. Examples of aquatic bugs are water boatmen, backswimmers, giant water bugs, water scorpions, and water striders.

Bugs have two sets of wings although in some species, the wings are greatly reduced in size and the animals cannot fly. The mouthparts of bugs are adapted for piercing and sucking. Most bugs use these mouthparts to feed on plant juices. A few are parasites of vertebrates, living on the animal's surface and feeding on its blood.

Most bugs have long, segmented antennae. They tend to have well-developed compound eyes, although some species have several simple eyes as well. Many species of bugs have glands that give off a strongly scented, distasteful odor when the insect is disturbed. The common name of one species, the stink bug, is evidence for this fact.

Some species of true bugs are brightly and boldly colored. In most cases, these bugs feed on plants that contain poisonous chemicals that also occur in the bugs. These chemicals cause the insects to taste bad, providing protection for them from predators. The bright coloring provides a warning to predators that their prey not only look beautiful, but also taste bad.

While many bugs attack agricultural crops and cause economic harm to humans, a few are health hazards also. Bed bugs, for example, feed by sucking the blood of birds or mammals, including humans. Although their bites are irritating, they do not carry disease. By contrast, the Central and South American bugs sometimes known as kissing bugs are known to transmit the parasitic protozoan that causes Chagas' disease. Chagas' disease is characterized by recurring fever and may cause serious damage to the heart muscles.

Life cycles

Insects have a complex life cycle that consists of a series of intricate transformations called metamorphoses. At each stage of its life cycle, an insect is likely to have very different body shapes, functions, and behaviors. The most complicated life cycles have four stages: egg, larva, pupa, and adult. Examples of insect orders with this life cycle include butterflies, moths, and true flies. Other orders of insects have a less complex development with only three stages: egg, nymph, and adult. Insect orders with this life cycle include the relatively primitive springtails and true bugs.

Most insects are nonsocial. However, some species have developed remarkably complex social behaviors, with large groups of closely related individuals living together and caring for the eggs and young of the group. In such groups, the young are usually the offspring of a single female, known as the queen. This social system is most common in bees, wasps, ants, and termites.

Insects and humans

A few species of insects are useful to humans. For example, we obtain honey from bees and silk from silk worms. Some insects, however, are detrimental because they transmit human diseases. For example, malaria, yellow fever, sleeping sickness, and certain types of encephalitis are caused by microorganisms. These microorganisms are transmitted by certain species of biting flies, especially mosquitoes. When one of these insects bites a human, it may ingest a disease-causing microorganism in the blood it drinks. When the insect bites a second person, it may then transfer that microorganismalong with the disease it causesto its second victim.

Other insects eat the leaves off trees and thereby cause substantial damage to commercial timber stands and to shade trees. Insects may also defoliate (remove the leaves from) agricultural plants, or they may feed on unharvested or stored grains, thus causing great economic losses. Some insects, particularly termites, cause enormous damage to wood, literally eating buildings constructed of that material. Pesticideschemicals that are toxic to insectsare sometimes used to control the populations of insects that are regarded as major pests.

[See also Agrochemicals; Butterflies; Cockroaches ]

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Insects


An insect is an invertebrate animal with six legs and a body that is clearly divided into three main segments. The heads of most insects have a pair of antennae, compound eyes, and large jaws. Insects inhabit nearly every part of Earth and make up the most numerous class of living animal. They are considered to be the most successful group of living creatures ever to have lived on Earth.

Insects belong to the phylum Arthropoda and make up its largest class. Well-known examples include bees, ants, butterflies, grasshoppers, beetles, moths, mosquitos, and the house fly. Insects are so diverse that there is probably no typical insect, although there is a basic insect anatomy or structure. An adult insect has three distinct body segments—the head, thorax, and abdomen. The head contains the sense organs like antennae and eyes, as well as three pairs of mouthparts that are adapted for either biting, chewing, puncturing, or sucking, depending on the species. The thorax has three segments, each of which has a pair of legs that are used for walking and clinging. If an insect has wings, they are attached at the thorax. Also located at the thorax are small tubelike openings called trachea that insects use to take in oxygen and expel carbon dioxide. Some of these openings are also found on the forward part of the abdomen. Since insect tissue gets oxygen directly through these tracheae, the circulatory system is fairly simple. The insect abdomen is used primarily for reproductive purposes. Digestion occurs in a three-part gut and wastes are excreted out of very specialized organs called Malpighian tubules. Named after the Italian anatomist (a person specializing in the structure of animals) who discovered them, these function like kidneys and remove waste from the insect's system. Insects also possess an exoskeleton, a hard outer support structure that protects their soft internal organs and provides some protection against predators.

Insects have been described as the dominant form of life on Earth. One writer even argues that if visitors from other planets came to Earth and studied its life forms, they might want to communicate first with an

insect because of their staggering diversity and overwhelming numbers that the insect represents. One reason for this steady success is the small size of insects. A small insect does not need as much food as a large animal does, so it is easier for an insect to find food. Insects also have highly specialized mouthparts and digestive systems that allow them to consume almost any plant in existence. If necessary, however, they will eat anything they can find. An insect's small size also allows it to hide more easily from its enemies, thus possibly enabling the insect to avoid predators and live longer.

Another reason for their success could be the distinct advantage having wings provide insects. Being able to fly means insects can easily escape earthbound predators, but it also confers the advantage of being able to leave a certain habitat if it proves difficult or dangerous to live there. Flying also allows insects to populate other habitats that most animals would have a hard time reaching. Altogether, their small size and flying ability gives insects a competitive advantage in the struggle for survival.

Another major reason that certain insects prosper is because they are social insects. Although some live independently of others, some insects live together in what are called colonies. A colony is a group of animals that live together and share work and food. Honeybees, termites, ants, and wasps are social insects. In a colony, an individual insect does not have to provide itself with food and shelter, since all the tasks needed for living are carried out by different members of the colony. Each member has a specific job to do, and it performs only that role and nothing else. For example, in an ant colony, a queen ant lays eggs and contributes to the growth of the colony; soldier ants guard the colony and do the fighting during an attack; nurse ants tend only to the queen, her eggs, and the larvae; and worker ants locate food outside the colony and bring it back for all. All of the roles are performed totally by instinct. The system works because each insect in a colony spends every day of its life doing the job it must do and nothing else. Besides being social, insects also have a staggering reproductive capacity. For example, if all the eggs of a single fly were to survive and reproduce through only six more generations, there would be more than 5,000,000,000,000 flies.

In many ways, insects are mankind's most aggressive competitor. They will eat crops as well as stored food. They can swarm and consume every green thing in sight. They also can destroy paper, wood, and cloth. They bite humans and other animals and transmit diseases.

On the other hand, insects are important and necessary pollinators of flowers and crops, and many beneficial insects (like the ladybug and praying mantis) attack or destroy many insects harmful to humans or crops. Bees provide honey as well as pollination. Overall, human beings have now learned that we cannot defeat or even diminish the range, extent, and diversity of the insect population. However, humans can control insects' negative effects by learning more about their habits, needs, and life cycles.

[See alsoInvertebrates ]

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225. Insects

See also 19. ANTS ; 40. BEES ; 44. BIOLOGY ; 64. BUTTERFLIES ; 430. ZOOLOGY .

acarophobia
a fear of itching or of the mites or ticks that cause it.
aeroscepsy, aeroscepsis
perception by means of the air, said to be a function of the antennae of insects.
bugology
Informal. entomology. bugologist , n.
coleopterology
the branch of entomology that studies beetles and weevils. coleopterological , adj. coleopterist , n.
dipterology
the branch of entomology that studies the order of insects Diptera, including houseflies, mosquitoes, and gnats.
entomology
the branch of zoology that studies insects. Also called insectology . entomologist , n. entomologie, entomological , adj.
entomomania
an abnormal love of insects.
entomophobia
an abnormal fear of insects.
ephemeron
anything shortlived, or of brief duration, especially certain types of insects such as the mayfly.
gynandromorphism
the condition of having one half of the body male and the other half female, as certain insects. gynandromorph , n. gynandromorphous , adj.
hemipterology
the branch of entomology that studies the order Hemiptera, including bedbugs, squashbugs, and aphids.
heteromorphism
1. the quality of differing in form from the standard or norm.
2. the condition of existing in different forms at different stages of development, as certain insects. heteromorphic , adj.
hymenopterology
the branch of entomology that studies the order Hytnenoptera, including bees, wasps, and ants.
hypermetamorphosis
a process by which an insect goes through more than the usual number of transformations, as the larva being metamorphosed more than once.
ichneumonology
the study of the life of the ichneumon fly.
insecticide
a substance used for killing insects. insecticidal , adj.
insectology
entomology.
myrmecology
the study of ants.
neoteny
the capacity or state of becoming sexually mature in the larval stage. neotenous , adj.
neuropterology
the branch of entomology that studies the order Neuroptera, including lacewings and ant lions.
orthopterology
the branch of entomology that studies the order Orthoptera, including cockroaches, grasshoppers, and mantises.
pediculophobia
an abnormal fear of lice. Also called phthiriophobia.
pediculosis
an infestation with lice; lousiness. pediculous, adj.
pesticide
any chemical substance used for killing pests, as insects, weeds, etc.
phthiriophobia
pediculophobia.
polymorphism
the occurrence of several forms or colors in one species of insect. polymorphous, adj.
stridulation
1. an action characteristic of some insects of producing a shrill, grating noise by chafing a serrated part of the body against a hard part.
2. the noise so produced. stridulator, n. stridulant, stridulatory, adj.
vespiary
1. a wasps nest.
2. a community or colony of wasps.
xenobiosis
communal life, such as that of ants, in which colonies of different species live together but do not share the raising of the young. xenobiotic , adj.
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Insects

Insects are invertebrates in the class Insecta, which contains 28 living orders. This class of the phylum Arthropoda is distinguished by a number of anatomical features, including an adult body that is typically divided into three parts (head, thorax, and abdomen), three pairs of segmented legs attached to the thorax, one pair of antennae, and ventilation of respiratory gases through pores called spiracles and along tubes called tracheae. Insect orders in the subclass Pterygota have two pair of wings as adults, but some relatively primitive orders in the subclass Apterygota are wingless.

Insects have a complex life cycle, with a series of intricate transformations called metamorphoses occurring between the stages, each of which is radically different in morphology, physiology, and behavior. The most complicated life cycles have four stages: egg, larva, pupa, and adult. Insect orders with this life cycle include butterflies and moths (Lepidoptera) and the true flies (Diptera). Other orders of insects have a less complex, more direct development, involving egg, nymph, and adult. Insect orders with this life cycle include the relatively primitive springtails (Collembola) and the true bugs (Hemiptera).

Most insects are nonsocial. However, some species have developed remarkably complex social behaviors, with large groups of closely related individuals living together and caring for the eggs and young of the group, which are usually the progeny of a single female, known as the queen. This social system is most common in the bees, wasps, and ants (Hymenoptera), and in the unrelated termites (Isoptera).

A few species of insects are useful to humans. Others are important factors in the transmission of diseases. For example, malaria, yellow fever, sleeping sickness, and certain types of encephalitis are caused by microorganisms transmitted by particular species of biting flies, especially mosquitoes. Other insects are important defoliators of trees, and can cause substantial damage to commercial timber stands and to shade trees. Insects may also defoliate agricultural plants, or may feed on unharvested or stored grains, causing great economic losses. Some insects, particularly termites, cause enormous damage to wood, literally eating buildings constructed of that material. Pesticideschemicals that are toxic to insectsare sometimes used to control the populations of insects regarded as major pests.

Taxonomists have recognized and named more than one million species of insectsmore than have been recognized in any other group of organisms. Of these, approximately three-quarters of a million have been described in some detail. To lend perspective of the vast number of insect species, there are a mere 6,200 bird and 5,800 reptile species known. There are over 10,000 species of ants alone. In addition, biologists believe that tens of millions of species of insects remain undiscovered, especially in tropical rainforests. Although the insect orders are poorly known, as many as 30 million species of insects may exist, many thought to be beetles (Coleoptera).

Globally, there is an enormous abundance and productivity of insects, and an extraordinary richness of species. These exploit a remarkable diversity of habitats, and are ecologically important as herbivores, predators, parasites, and scavengers. As a result of these attributes, insects are considered to be one of the most successful group of organisms on Earth, if not the most successful.

See also Pesticides.

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Insects

Insects are invertebrates in the class Insecta, which contains 28 living orders. This class of the phylum Arthropoda is distinguished by a number of anatomical features, including an adult body that is typically divided into three parts (head, thorax, and abdomen), three pairs of segmented legs attached to the thorax, one pair of antennae, and ventilation of respiratory gases through pores called spiracles and along tubes called tracheae. Insect orders in the subclass Pterygota have two pair of wings as adults, but some relatively primitive orders in the subclass Apterygota are wingless.

Insects have a complex life cycle, with a series of intricate transformations (called metamorphosis ) occurring between the stages, each of which is radically different in morphology, physiology , and behavior . The most complicated life cycles have four stages: egg, larva, pupa, and adult. Examples of insect orders with this life cycle include butterflies and moths (Lepidoptera) and the true flies (Diptera). Other orders of insects have a less complex, more direct development, involving egg, nymph, and adult. Insect orders with this life cycle include the relatively primitive springtails (Collembola) and the true bugs (Hemiptera).

Most insects are nonsocial. However, some species have developed remarkably complex social behaviors, with large groups of closely related individuals living together and caring for the eggs and young of the group, which are usually the progeny of a single female, known
as the queen. This social system is most common in the bees , wasps , and ants (Hymenoptera), and in the unrelated termites (Isoptera).

A few species of insects are useful to humans. Some insects, however, are important factors in the transmission of human diseases. For example, malaria , yellow fever , sleeping sickness , and certain types of encephalitis are caused by microorganisms , but are transmitted by particular species of biting flies , especially mosquitoes . Other insects are important defoliators of trees, and can thereby cause substantial damage to commercial timber stands and to shade trees. Insects may also defoliate agricultural plants, or may feed on unharvested or stored grains, thus causing great economic losses. Some insects, particularly termites, cause enormous damage to wood , literally eating buildings constructed of that material. Pesticides—chemicals that are toxic to insects—are sometimes used to control the populations of insects regarded as major pests .

Taxonomists have recognized and named more than one million species of insects—more than have been recognized in any other group of organisms. Of these, approximately three-quarter of a million have been described in some detail. To lend perspective of the vast number of insect species, there are a mere 6,200 bird and 5,800 reptile species described. There are over 10,000 known species of ants alone. In addition, biologists believe that tens of millions of species of insects remain undiscovered. One estimate is that as many as 30 million species of insects inhabit Earth . Most of these are thought to be beetles (Coleoptera). In fact, all of the insect orders are poorly known. Most of these undiscovered species of insects occur in tropical rainforests, especially in the canopy.

Globally, there is an enormous abundance and productivity of insects, and an extraordinary richness of species. These exploit a remarkable diversity of habitats, and are ecologically important as herbivores, predators, parasites , and scavengers. As a result of these attributes, insects are considered to be one of the most successful group of organisms on Earth, if not the most successful.

See also Pesticides.

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insect Any of more than a million species of small, invertebrate animals of the class Insecta, including the beetle, bug, butterfly, ant and bee. There are more species of insects than all other species combined. Adult insects have three pairs of jointed legs, usually two pairs of wings, and a segmented body with a horny outer covering or exoskeleton. The head has three pairs of mouthparts, a pair of compound eyes, three pairs of simple eyes, and a pair of antennae. Most insects can detect a wide range of sounds through ultra-sensitive hairs on various parts of their bodies. Some can ‘sing’ or make sounds by rubbing together parts of their bodies. Most insects are plant-eaters, many being serious farm and garden pests. Some prey on small animals, especially other insects, and a few are scavengers. There are two main kinds of mouthparts – chewing and sucking. Reproduction is usually sexual. Most insects go through four distinct life stages, in which complete metamorphosis is said to take place. The stages are ovum (egg), larva (caterpillar or grub), pupa (chrysalis), and adult (imago). Young grasshoppers and some other insects, called nymphs, resemble wingless miniatures of their parents. The nymphs develop during a series of moults (incomplete metamorphosis). Silverfish and a few other primitive, wingless insects do not undergo metamorphosis. Phylum Arthropoda See also arthropod

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Insecta (Hexapoda, insects; phylum Arthropoda, subphylum Atelocerata) Class of arthropods that have three pairs of legs and, usually, two pairs of wings borne on the thorax. Typically, there is a single pair of antennae and one pair of compound eyes. Gas exchange takes place through a system of tracheae and the gonoducts open at the posterior end of the body. The oldest fossil insects occur in Devonian rocks, and the first winged representatives are known from Carboniferous rocks. Dragonflies and beetles were established before the end of the Palaeozoic; social varieties such as ants and wasps are present in Cretaceous sediments. The evolution of the flowering plants had a marked influence on insect development, so that many new forms appeared in the Cretaceous and Tertiary Periods. More than 750 000 extant species of insects have been described. This is larger than the number of species belonging to all other animal classes combined.

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Insecta (Hexapoda, insects; phylum Arthropoda) Class of arthropods that have three pairs of legs and, usually, two pairs of wings borne on the thorax. Typically, there is a single pair of antennae and one pair of compound eyes. Gas exchange takes place through a tracheal system and the gonoducts open at the posterior end of the body. The oldest fossil insects occur in Devonian rocks, and the first winged representatives are known from Carboniferous rocks. Dragonflies and beetles were established before the end of the Palaeozoic; social varieties such as ants and wasps are present in Cretaceous sediments. The evolution of the flowering plants had a marked influence on insect development, so that many new forms appeared in the Cretaceous and Tertiary Period. About 950 000 extant species of insects have been described. This is larger than the number of species belonging to all other animal classes combined.

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