Kingdom: Animalia... Phylum: Arthropoda... Class: Insecta...

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Insects (Class Insecta) are a major group of arthropods and the most diverse group of animals on the Earth, with over a million described species more than half of all known living organisms. With published estimates of undescribed species as high as 30 million, thus potentially, we can affirm that, insects are over 90% of the life on earth. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans where crustaceans tend to predominate instead. There are approximately 5,000 dragonfly species, 2,000 praying mantis, 20,000 grasshopper, 170,000 butterfly and moth, 120,000 fly, 82,000 true bug, 360,000 beetle, and 110,000 bee, wasp and ant species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million.  The study of insects is from the Latin insectus, meaning "cut into sections" also from the Greek εντομον, is meaning "cut into sections".



Social insects, such as the termites, ants and many bees and wasps, are the most familiar species of eusocial animal. They live together in large well-organized colonies that may be so tightly integrated and genetically similar that the colonies of some species are sometimes considered superorganisms. It is sometimes argued that the various species of honey bee are the only invertebrates (and indeed one of the few non-human groups) to have evolved a system of abstract symbolic communication (i.e., where a behaviour is used to represent and convey specific information about something in the environment), called the "dance language" - the angle at which a bee dances represents a direction relative to the sun, and the length of the dance represents the distance to be flown.
Only those insects which live in nests or colonies demonstrate any true capacity for fine-scale spatial orientation or "homing" - this can be quite sophisticated, however, and allow an insect to return unerringly to a single hole a few millimetres in diameter among a mass of thousands of apparently identical holes all clustered together, after a trip of up to several kilometres' distance, and (in cases where an insect hibernates) as long as a year after last viewing the area (a phenomenon known as philopatry). A few insects migrate, but this is a larger-scale form of navigation, and often involves only large, general regions (e.g., the overwintering areas of the Monarch butterfly).



Adult modern insects range in size from a 0.139 mm to a 55.5 cm. The heaviest documented insect was 70 g. Insects possess segmented bodies supported by an exoskeleton. The segments of the body are organized into three regions, or tagmata; a head, a thorax, and an abdomen. The head supports a pair of sensory antennae, a pair of compound eyes, one to three simple eyes ("ocelli") and three sets of variously modified appendages that form the mouthparts. The thorax has six legs…one pair each for the prothorax, mesothorax and the metathorax segments making up the thorax, and two or four wings. The abdomen is made up of eleven segments some of which may be reduced or fused, has most of the digestive, respiratory, excretory and reproductive internal structures.
Insect respiration is accomplished without lungs, but instead insects possess a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to body tissues. Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced; it has no closed vessels.

Most insects hatch from eggs, but others are ovoviviparous or viviparous, and all undergo a series of moults as they develop and grow in size. This manner of growth is necessitated by the inelastic exoskeleton. Moulting is a process by which the individual escapes the confines of the exoskeleton in order to increase in size, then grows a new and larger outer covering. In some insects, the young are called nymphs and are similar in form to the adult except that the wings are not developed until the adult stage. In some species, an egg hatches to produce a larva, which is generally worm-like in form, and can be divided into five different forms; eruciform (caterpillar-like), scarabaeiform (grublike), campodeiform (elongated, flattened, and active), elateriform (wireworm-like) and vermiform (maggot-like). The larva grows and eventually becomes a pupa, a stage sealed within a cocoon in some species. There are three types of pupae; obtect (the pupa is compact with the legs and other appendages enclosed), exarate (where the pupa has the legs and other appendages free and extended) and coarctate (where the pupa develops inside the larval skin). In the pupal stage, the insect undergoes considerable change in form to emerge as an adult, or imago. Butterflies are an example of an insect that undergoes complete metamorphosis.

Many insects possess very sensitive and/or specialized organs of perception. Some insects such as bees can perceive ultraviolet wavelengths, or detect polarized light, while the antennae of male moths can detect the pheromones of female moths over distances of many kilometres. There is a pronounced tendency for there to be a trade-off between visual acuity and chemical or tactile acuity, such that most insects with well-developed eyes have reduced or simple antennae, and vice-versa. There are a variety of different mechanisms by which insects perceive sound, and it is by no means universal; the general pattern, however, is that if an insect can produce sound, then it can also hear sound, though the range of frequencies they can hear is often quite narrow (and may in fact be limited to only the frequency that they themselves produce). Some nocturnal moths can perceive the ultrasonic emissions of bats, a mechanism which helps them avoid predation. Certain predatory and parasitic insects can detect the characteristic sounds made by their prey/hosts. Bloodsucking insects have special sensory structures that can detect infrared emissions, and use them to home in on their hosts.

Most insects lead short lives as adults, and rarely interact with one another except to mate, or compete for mates. A small number exhibit some form of parental care, where they will at least guard their eggs, and sometimes continue guarding their offspring until adulthood, and possibly even actively feeding them. Another simple form of parental care is to construct a nest (a burrow or an actual construction, either of which may be simple or complex), store provisions in it, and lay an egg upon those provisions. The adult does not contact the growing offspring, but it nonetheless does provide food. This sort of care is typical of bees and various types of wasps.

Insects were the earliest organisms to produce sounds and to sense them. Soundmaking in insects is achieved mostly by mechanical action of appendages. In the grasshoppers and crickets this is achieved by stridulation. The cicadas have the loudest sounds among the insects and have special modifications to their body and musculature to produce and amplify sounds. Some species have been measured at 106.7 decibels at a distance of 50 cm. Some insects, can hear ultrasound and take evasive action when they sense detection by bats.

In addition to the use of sound for communication, a wide range of insects have evolved chemical means for communication. These chemicals, termed semiochemicals, are often derived from plant metabolites include those meant to attract, repel and provide other kinds of information. While some chemicals are targeted at individuals of the same species, others are used for communication across species. The use of scents is especially well known to have developed in social insects.

Insects are the only group of invertebrates to have developed flight. The evolution of insect wings has been a subject of debate. Some proponents suggest that the wings are para-notal in origin while others have suggested they are modified gills. In the Carboniferous age, some of the Meganeura dragonflies had as much as a 50 cm (20 in) wide wingspan. The appearance of gigantic insects has been found to be consistent with high atmospheric oxygen. The percentage of oxygen in the atmosphere found from ice core-samples was as high as 35% compared to the current 21%. In addition to powered flight, many of the smaller insects are also dispersed by winds. These include the aphids which are often transported long distances by low-level jet streams.

Cockroaches are amongst the fastest insect runners and at full speed actually adopt a bipedal run to reach a high velocity in proportion to their body size. A few insects have evolved to walk on the surface of the water, especially the bugs of the family, Gerridae, also known as water striders. Insect walking is of particular interest as an alternative form of locomotion to the use of wheels for robots

A large number of insects live either parts or the whole of their lives underwater. In many orders the immature stages are spent in water while the adults are either aerial or terrestrial in habit. A few species spend a part of their adult life either under or over water. Some species like the water striders are capable of walking on the surface of water. They can do this because their claws are not at the tips of the legs as in most insects, but recessed in a special groove further up the leg; this prevents the claws from piercing the water's surface film.

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, estimated at 396-407 million years old. This species already possessed dicondylic mandibles, 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. Insects can be divided into two groups, historically treated as subclasses: Apterygota (wingless) and Pterygota (winged).
Pollination is a trade between plants that need to reproduce, and pollinators that receive rewards of nectar and pollen. A serious environmental problem today is the decline of populations of pollinator insects, and a number of species of insects are now cultured primarily for pollination management in order to have sufficient pollinators in the field, orchard or greenhouse at bloom time.
Insects also produce useful substances such as honey, wax, lacquer and silk. Honey bees have been cultured by humans for thousands of years for honey, although contracting for crop pollination is becoming more significant for beekeepers. The silkworm has greatly affected human history, as silk-driven trade established relationships between China and the rest of the world. Fly larvae were formerly used to treat wounds to prevent or stop gangrene, as they would only consume dead flesh. This treatment is finding modern usage in some hospitals. Adult insects such as crickets, and insect larvae of various kinds are also commonly used as fishing bait.


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English: Insect
Insects are over 90% of the life on earth.

Espagnol: Insectos
Los Insectos estan mas de 90% de la vida sobre la terra.

Français: Insectes
Les Insectes font plus de 90% de la vie sur la terre.

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