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These are simple text files which sit on your computer, and are only used by us and our trusted partners. To find out about managing cookies, please see our Cookies Policy. USA Today politics blog. Report: Trump rented to Iranian bank with terror ties 5.3k Shares. Online periodical for British expatriates. Provides resources by region and includes finding mentors, latest news, finance, health care, property, education and a.Insect - Wikipedia. Insects (from Latininsectum, a calque of Greek. They are the most diverse group of animals on the planet, including more than a million described species and representing more than half of all known living organisms. ![]() ![]() Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat, and can include a passive pupal stage in those groups that undergo 4- stage metamorphosis (see holometabolism). Insects that undergo 3- stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 5. The most diverse insect groups appear to have coevolved with flowering plants. Adult insects typically move about by walking, flying or sometimes swimming (see . As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles. ![]() Insects are the only invertebrates to have evolved flight. Many insects spend at least part of their lives under water, with larval adaptations that include gills, and some adult insects are aquatic and have adaptations for swimming. Some species, such as water striders, are capable of walking on the surface of water. Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well- organized colonies. Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: cricketsstridulate, or rub their wings together, to attract a mate and repel other males. Lampyridae in the beetle order communicate with light. Humans regard certain insects as pests, and attempt to control them using insecticides and a host of other techniques. Some insects damage crops by feeding on sap, leaves or fruits. A few parasitic species are pathogenic. Some insects perform complex ecological roles; blow- flies, for example, help consume carrion but also spread diseases. Insect pollinators are essential to the life- cycle of many flowering plant species on which most organisms, including humans, are at least partly dependent; without them, the terrestrial portion of the biosphere (including humans) would be devastated. Silkworms and bees have been used extensively by humans for the production of silk and honey, respectively. In some cultures, people eat the larvae or adults of certain insects. Etymology. Pliny the Elder introduced the Latin designation as a loan- translation of the Greek word . Translations of Aristotle's term also form the usual word for . Pictured are some of the possible shapes of antennae. The evolutionary relationship of insects to other animal groups remains unclear. Although traditionally grouped with millipedes and centipedes. In the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea. However, upon closer examination, their features differ significantly; most noticeably, they do not have the six- legged characteristic of adult insects. In 2. 00. 8, researchers at Tufts University uncovered what they believe is the world's oldest known full- body impression of a primitive flying insect, a 3. Carboniferous period. It may have superficially resembled a modern- day silverfish insect. This species already possessed dicondylic mandibles (two articulations in the mandible), a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period. The flies and moths along with the fleas evolved from the Mecoptera. The origins of insect flight remain obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects had an additional pair of winglets attaching to the first segment of the thorax, for a total of three pairs. As of 2. 00. 9, no evidence suggests the insects were a particularly successful group of animals before they evolved to have wings. During this era, some giant dragonfly- like forms reached wingspans of 5. This gigantism may have been due to higher atmospheric oxygen levels that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor. Most extinct orders of insects developed during the Permian period that began around 2. Many of the early groups became extinct during the Permian- Triassic extinction event, the largest mass extinction in the history of the Earth, around 2. A number of highly successful insect groups evolved in conjunction with flowering plants, a powerful illustration of coevolution. Insects from this period on are often found preserved in amber, often in perfect condition. The body plan, or morphology, of such specimens is thus easily compared with modern species. The study of fossilized insects is called paleoentomology. Evolutionary relationships. The earliest vertebrates on land existed 4. Through gradual evolutionary change, insectivory was the next diet type to evolve. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination, are beneficial to both organisms. Coevolution has led to the development of very specific mutualisms in such systems. Taxonomy. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that the Hexapoda are polyphyletic (where the last common ancestor was not a member of the group), with the entognath classes having separate evolutionary histories from the Insecta. The following represents the best- supported monophyletic groupings for the Insecta. Insects can be divided into two groups historically treated as subclasses: wingless insects, known as Apterygota, and winged insects, known as Pterygota. The Apterygota consist of the primitively wingless order of the silverfish (Thysanura). Archaeognatha make up the Monocondylia based on the shape of their mandibles, while Thysanura and Pterygota are grouped together as Dicondylia. The Thysanura themselves possibly are not monophyletic, with the family Lepidotrichidae being a sister group to the Dicondylia (Pterygota and the remaining Thysanura). Neoptera can further be divided into incomplete metamorphosis- based (Polyneoptera and Paraneoptera) and complete metamorphosis- based groups. It has proved difficult to clarify the relationships between the orders in Polyneoptera because of constant new findings calling for revision of the taxa. For example, the Paraneoptera have turned out to be more closely related to the Endopterygota than to the rest of the Exopterygota. The recent molecular finding that the traditional louse orders Mallophaga and Anoplura are derived from within Psocoptera has led to the new taxon Psocodea. Matters that have incurred controversy include Strepsiptera and Diptera grouped together as Halteria based on a reduction of one of the wing pairs . Fleas are now thought to be closely related to boreid mecopterans. If one works with a more specific order or even a family, the term may also be made specific to that order or family, for example systematic dipterology. Diversity. Of the 2. Coleoptera, Diptera, Hymenoptera and Lepidoptera. A recent study estimated the number of beetles at 0. The segments of the body are organized into three distinctive but interconnected units, or tagmata: a head, a thorax and an abdomen. The thorax has six segmented legs. The abdomen consists of eleven segments, though in a few species of insects, these segments may be fused together or reduced in size. The abdomen also contains most of the digestive, respiratory, excretory and reproductive internal structures. Of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and sclerites. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the ocelli are normally. This is because the primary axis of the head is rotated 9. In some species, this region is modified and assumes a different name. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax, with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings. Each segment is dilineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum (or notum) to distinguish it from the abdominal terga. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, the mesopleura and metapleura, as well as the mesosternum and metasternum, are used. Each segment of the abdomen is represented by a sclerotized tergum and sternum. Terga are separated from each other and from the adjacent sterna or pleura by membranes. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite. Ventral sclerites are sometimes called laterosternites.
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