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Insects (from Latin insectum) are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen ), three pairs of jointed legs, compound eyes, and a pair of antennae.
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insect, (class Insecta or Hexapoda), any member of the largest class of the phylum Arthropoda, which is itself the largest of the animal phyla. Insects have segmented bodies, jointed legs, and external skeletons (exoskeletons). Insects are distinguished from other arthropods by their body, which is divided into three major regions: (1) the head, which bears the mouthparts, eyes, and a pair of antennae, (2) the three-segmented thorax, which usually has three pairs of legs (hence “Hexapoda”) in adults and usually one or two pairs of wings, and (3) the many-segmented abdomen, which contains the digestive, excretory, and reproductive organs.
In a popular sense, “insect” usually refers to familiar pests or disease carriers, such as bedbugs, houseflies, clothes moths, Japanese beetles, aphids, mosquitoes, fleas, horseflies, and hornets, or to conspicuous groups, such as butterflies, moths, and beetles. Many insects, however, are beneficial from a human viewpoint; they pollinate plants, produce useful substances, control pest insects, act as scavengers, and serve as food for other animals (see below Importance). Furthermore, insects are valuable objects of study in elucidating many aspects of biology and ecology. Much of the scientific knowledge of genetics has been gained from fruit fly experiments and of population biology from flour beetle studies. Insects are often used in investigations of hormonal action, nerve and sense organ function, and many other physiological processes. Insects are also used as environmental quality indicators to assess water quality and soil contamination and are the basis of many studies of biodiversity.
In numbers of species and individuals and in adaptability and wide distribution, insects are perhaps the most eminently successful group of all animals. They dominate the present-day land fauna with about 1 million described species. This represents about three-fourths of all described animal species. Entomologists estimate the actual number of liv...
The majority of insects are small, usually less than 6 mm (0.2 inch) long, although the range in size is wide. Some of the feather-winged beetles and parasitic wasps are almost microscopic, while some tropical forms such as the hercules beetles, African goliath beetles, certain Australian stick insects, and the wingspan of the hercules moth can be as large as 27 cm (10.6 inches).
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In many species the difference in body structure between the sexes is pronounced, and knowledge of one sex may give few clues to the appearance of the other sex. In some, such as the twisted-wing insects (Strepsiptera), the female is a mere inactive bag of eggs, and the winged male is one of the most active insects known. Modes of reproduction are quite diverse, and reproductive capacity is generally high. Some insects, such as the mayflies, feed only in the immature or larval stage and go without food during an extremely short adult life. Among social insects, queen termites may live for up to 50 years, whereas some adult mayflies live less than two hours.
Some insects advertise their presence to the other sex by flashing lights, and many imitate other insects in colour and form and thus avoid or minimize attack by predators that feed by day and find their prey visually, as do birds, lizards, and other insects.
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Learn about insects, the largest and most diverse class of arthropods, with segmented bodies, jointed legs, and external skeletons. Explore their diversity, importance, adaptations, and behaviour with Britannica's comprehensive article.
Learn about the diversity, evolution, and ecology of insects, the most abundant animals on Earth. Explore stunning photos, videos, and stories of insects and their interactions with humans and other species.
The body of an insect has three main parts: a head, a thorax, and an abdomen. On the head are an insect's compound eyes , its two antennae (they feel and smell things), and its mouth. On the thorax, insects have wings and legs.
Learn about the insects, the largest arthropod class with nearly 1 million known species and diverse body plans. Find out how insects are classified by wing form, metamorphosis, and other features, and see examples of honeybee, mayfly, caddisfly, and thrips.
Learn about insects from aphids to yellowjackets in this 1,276-page volume with 270 articles, 1,000 figures, and 3,000 references. The Encyclopedia of Insects covers insect anatomy, physiology, evolution, behavior, ecology, and more.
Insects (from Latin insectum) are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen ), three pairs of jointed legs, compound eyes, and a pair of antennae.
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