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| Beetles'" are the group of insects with the largest number of known species. They are placed in the order "'Coleoptera'" (from Greek, "koleos", "sheath"; and, "pteron", "wing", thus "sheathed wing"), which contains more described species than in any other order in the animal kingdom, constituting about 25% of all known life-forms. 40% of all described insect species are beetles (about 350,000 species), and new species are frequently discovered. Estimates put the total number of species, described and undescribed, at between 5 and 8 million. Beetles can be found in almost all habitats, but are not known to occur in the sea or in the polar regions. They interact with their ecosystems in several ways. They often feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. Some species are prey of various animals including birds and mammals. Certain species are agricultural pests, such as the Colorado potato beetle "Leptinotarsa decemlineata", the boll weevil "Anthonomus grandis", the red flour beetle "Tribolium castaneum", and the mungbean or cowpea beetle "Callosobruchus maculatus", while other species of beetles are important controls of agricultural pests. For example, beetles in the family Coccinellidae ("ladybirds" or "ladybugs") consume aphids, scale insects, thrips, and other plant-sucking insects that damage crops. Description. The name "Coleoptera" was given by Aristotle for the hardened shield-like forewing (coleo= shield+ ptera= wing). Other characters of this group which are believed to be monophyletic include a holometabolous life cycle; having a prothorax that is distinct from and freely articulating with the mesothorax; the meso- and meta-thoracic segments fusing to form a pterothorax; a depressed body shape with the legs on the ventral surface; the coxae of legs recessed into cavities formed by heavily sclerotized thoracic sclerites; the abdominal sternites more sclerotized than the tergites; antennae with 11 or fewer segments; and terminal genitalic appendages retracted into the abdomen and invisible at rest. The general anatomy of beetles is quite uniform, although specific organs and appendages may vary greatly in appearance and function between the many families in the order. Like all insects, beetles' bodies are divided into three sections: the head, the thorax, and the abdomen. When viewed from below, the thorax is that part from which all three pairs of legs and both pairs of wings arise. The abdomen is everything posterior to the thorax. When viewed from above, most beetles appear to have three clear sections, but this is deceptive: on the beetle's upper surface, the middle "section" is a hard plate called the pronotum, which is only the front part of the thorax; the back part of the thorax is concealed by the beetle's wings. Like all arthropods, beetles are segmented organisms, and all three of the major sections of the body are themselves composed of several further segments, although these are not always readily discernible. This further segmentation is usually best seen on the abdomen. Beetles are generally characterised by a particularly hard exoskeleton and hard forewings (elytra). The beetle's exoskeleton is made up of numerous plates called sclerites, separated by thin sutures. This design creates the armoured defences of the beetle while maintaining flexibility. The elytra are not used for flight, but tend to cover the hind part of the body and protect the second pair of wings ("alae"). The elytra must be raised in order to move the hind flight wings. A beetle's flight wings are crossed with veins and are folded after landing, often along these veins, and are stored below the elytra. In some beetles, the ability to fly has been lost. These include the ground beetles (family Carabidae) and some "true weevils" (family Curculionidae), but also some desert and cave-dwelling species of other families. Many of these species have the two elytra fused together, forming a solid shield over the abdomen. In a few families, both the ability to fly and the elytra have been lost, with the best known example being the glow-worms of the family Phengodidae, in which the females are larviform throughout their lives. Beetles have mouthparts similar to those of grasshoppers. Of these parts, the most commonly known are probably the mandibles, which appear as large pincers on the front of some beetles. The mandibles are a pair of hard, often tooth-like structures that move horizontally to grasp, crush, or cut food or enemies (see defence, below). Two pairs of finger-like appendages are found around the mouth in most beetles, serving to move food into the mouth. These are the maxillary and labial palpi. The eyes are compound and may display remarkable adaptability, as in the case of whirligig beetles (family Gyrinidae), in which the eyes are split to allow a view both above and below the waterline. Other species also have divided eyes — some longhorn beetles (family Cerambycidae) and weevils — while many beetles have eyes that are notched to some degree. A few beetle genera also possess ocelli, which are small, simple eyes usually situated farther back on the head (on the vertex). Beetles' antennae are primarily organs of smell, but may also be used to feel out a beetle's environment physically. They may also be used in some families during mating, or among a few beetles for defence. Antennae vary greatly in form within the Coleoptera, but are often similar within any given family. In some cases, males and females of the same species will have different antennal forms. Antennae may be clavate (flabellate and lamellate are sub-forms of clavate, or clubbed antennae), filiform, geniculate, moniliform, pectinate, or serrate. For images of these antennal forms see antenna (biology). The legs, which are multi-segmented, end in two to five small segments called tarsi. Like many other insect orders beetles bear claws, usually one pair, on the end of the last tarsal segment of each leg. While most beetles use their legs for walking, legs may be variously modified and adapted for other uses. Among aquatic families — Dytiscidae, Haliplidae, many species of Hydrophilidae and others — the legs, most notably the last pair, are modified for swimming and often bear rows of long hairs to aid this purpose. Other beetles have fossorial legs that are widened and often spined for digging. Species with such adaptations are found among the scarabs, ground beetles, and clown beetles (family Histeridae). The hind legs of some beetles, such as flea beetles (within Chrysomelidae) and flea weevils (within Curculionidae), are enlarged and designed for jumping. Oxygen is obtained via a tracheal system. Air enters a series of tubes along the body through openings called spiracles, and is then taken into increasingly finer fibres. Pumping movements of the body force the air through the system. Beetles have hemolymph instead of blood, and the open circulatory system of the beetle is powered by a tube-like heart attached to the top inside of the thorax. Development. Beetles are endopterygotes with complete metamorphosis. A single female may lay from several dozen to several thousand eggs during her lifetime. Eggs are usually laid according to the substrate the larva will feed on upon hatching. Among others, they can be laid loose in the substrate (e.g. flour beetle), laid in clumps on leaves (e.g. Colorado potato beetle), or individually attached (e.g. mungbean beetle and other seed borers) or buried in the medium (e.g. carrot weevil). The larva is usually the principal feeding stage of the beetle life cycle. Larvae tend to feed voraciously once they emerge from their eggs. Some feed externally on plants, such as those of certain leaf beetles, while others feed within their food sources. Examples of internal feeders are most Buprestidae and longhorn beetles. The larvae of many beetle families are predatory like the adults (ground beetles, ladybirds, rove beetles). The larval period varies between species but can be as long as several years. Beetle larvae can be differentiated from other insect larvae by their hardened, often darkened head, the presence of chewing mouthparts, and spiracles along the sides of the body. Like adult beetles, the larvae are varied in appearance, particularly between beetle families. Beetles whose larvae are somewhat flattened and are highly mobile are the ground beetles, some rove beetles, and others; their larvae are described as campodeiform. Some beetle larvae resemble hardened worms with dark head capsules and minute legs. These are elateriform larvae, and are found in the click beetle (Elateridae) and darkling beetle (Tenebrionidae) families. Some elateriform larvae of click beetles are known as wireworms. Beetles in the families of the Scarabaeoidea have short, thick larvae described as scarabaeiform, but more commonly known as grubs. All beetle larvae go through several instars, which are the developmental stages between each moult. In many species the larvae simply increase in size with each successive instar as more food is consumed. In some cases, however, more dramatic changes occur. Among certain beetle families or genera, particularly those that exhibit parasitic lifestyles, the first instar (the planidium) is highly mobile in order to search out a host, while the following instars are more sedentary and remain on or within their host. This is known as hypermetamorphosis; examples include the blister beetles (family Meloidae) and some rove beetles, particularly those of the genus "Aleochara". As with all endopterygotes, beetle larvae pupate, and from this pupa emerges a fully formed, sexually mature adult beetle, or imago. Adults have an extremely variable lifespan, from weeks to years, depending on the species. Reproduction. Beetles may display extremely intricate behaviour when mating. Pheromone communication is thought to be important in the location of a mate. Conflict can play a part in the mating rituals of species such as burying beetles (genus "Nicrophorus") where conflicts between males and females rage until only one of each is left, thus ensuring reproduction by the strongest and fittest. Many male beetles are territorial and will fiercely defend their small patch of territory from intruding males. In such species, the males may often have horns on the head and or thorax, making their overall body lengths greater than those of the females, unlike most insects. Pairing is generally short but in some cases will last for several hours. During pairing sperm cells are transferred to the female to fertilise the egg. Parental care varies between species, ranging from the simple laying of eggs under a leaf to certain scarab beetles, which construct underground structures complete with a supply of dung to house and feed their young. Other beetles are leaf rollers, biting sections of leaves to cause them to curl inwards, then laying their eggs, thus protected, inside. Defense. Beetles and their larvae have a variety of strategies to avoid being attacked by predators or parasitoids. These include camouflage, mimicry, toxicity, and active defense. Camouflage involves the use of colouration or shape to blend into the surrounding environment. This sort of protective coloration is common and widespread among beetle families, especially those that feed on wood or vegetation, such as many of the leaf beetles (family Chrysomelidae) or weevils. In some of these species, sculpturing or various coloured scales or hairs cause the beetle to resemble bird dung or other inedible objects. Many of those that live in sandy environments blend in with the coloration of the substrate. Another defence that often uses colour or shape to deceive potential enemies is mimicry. A number of longhorn beetles (family Cerambycidae) bear a striking resemblance to wasps, which helps them avoid predation even though the beetles are in fact harmless. This defence can be found to a lesser extent in other beetle families, such as the scarab beetles. Beetles may combine their colour mimicry with behavioural mimicry, acting like the wasps they already closely resemble. Many beetle species, including ladybirds, blister beetles, and lycid beetles can secrete distasteful or toxic substances to make them unpalatable or even poisonous. These same species often exhibit aposematism, where bright or contrasting colour patterns warn away potential predators, and there are, not surprisingly, a great many beetles and other insects that mimic these chemically-protected species. Large ground beetles and longhorn beetles may defend themselves using strong mandibles and or spines or horns to forcibly persuade a predator to seek out easier prey. Others, such as bombardier beetles (within Carabidae), may spray chemicals from their abdomen to repel predators. Feeding. Besides being abundant and varied, the Coleoptera are able to exploit the wide diversity of food sources available in their many habitats. Some are omnivores, eating both plants and animals. Other beetles are highly specialised in their diet. Many species of leaf beetles, longhorn beetles, and weevils are very host specific, feeding on only a single species of plant. Ground beetles and rove beetles (family Staphylinidae), among others, are primarily carnivorous and will catch and consume many other arthropods and small prey such as earthworms and snails. While most predatory beetles are generalists, a few species have more specific prey requirements or preferences. Decaying organic matter is a primary diet for many species. This can range from dung, which is consumed by coprophagous species such as certain scarab beetles (family Scarabaeidae), to dead animals, which are eaten by necrophagous species such as the carrion beetles (family Silphidae). Some of the beetles found within dung and carrion are in fact predatory, such as the clown beetles, preying on the larvae of coprophagous and necrophagous insects. Adaptations to the environment. Aquatic beetles use several techniques for retaining air beneath the water's surface. Beetles of the family Dytiscidae hold air between the abdomen and the elytra when diving. Hydrophilidae have hairs on their under surface that retain a layer of air against their bodies. Adult crawling water beetles use both their elytra and their hind coxae (the basal segment of the | The telephone'" (from the, "tēle", "far" and φωνή, "phōnē", "voice") is a telecommunications device that is used to transmit and receive electronically or digitally encoded sound (most commonly speech) between two or more people conversing. It is one of the most common household appliances in the developed world today. Most telephones operate through transmission of electric signals over a complex telephone network which allows almost any phone user to communicate with almost any other user. Graphic symbols used to designate telephone service or phone-related information in print, signs, and other media include,, and. Basic principle. A traditional landline telephone system, also known as "plain old telephone service" (POTS), commonly handles both signaling and audio information on the same twisted pair of insulated wires: the telephone line. Although originally designed for voice communication, the system has been adapted for data communication such as Telex, Fax and Internet communication. The signaling equipment consists of a bell, beeper, light or other device to alert the user to incoming calls, and number buttons or a rotary dial to enter a telephone number for outgoing calls. A twisted pair line is preferred as it is more effective at rejecting electromagnetic interference (EMI) and crosstalk than an untwisted pair. A calling party wishing to speak to another party will pick up the telephone's handset, thus operating a button switch or "switchhook", which puts the telephone into an active state or "off hook" by connecting the transmitter (microphone), receiver (speaker) and related audio components to the line. This circuitry has a low resistance (less than 300 Ohms) which causes DC current (48 volts, nominal) from the telephone exchange to flow through the line. The exchange detects this DC current, attaches a digit receiver circuit to the line, and sends a dial tone to indicate readiness. On a modern telephone, the calling party then presses the number buttons in a sequence corresponding to the telephone number of the called party. The buttons are connected to a tone generator that produces DTMF tones which are sent to the exchange. A rotary dial telephone employs pulse dialing, sending electrical pulses corresponding to the telephone number to the exchange. (Most exchanges are still equipped to handle pulse dialing.) Provided the called party's line is not already active or "busy", the exchange sends an intermittent ringing signal (generally over 100 volts AC) to alert the called party to an incoming call. If the called party's line is active, the exchange sends a busy signal to the calling party. However, if the called party's line is active but has call waiting installed, the exchange sends an intermittent audible tone to the called party to indicate an incoming call. When a landline phone is inactive or "on hook", its alerting device is connected across the line through a capacitor, which prevents DC current from flowing through the line. The circuitry at the telephone exchange detects the absence of DC current flow and thus that the phone is on hook with only the alerting device electrically connected to the line. When a party initiates a call to this line, the ringing signal transmitted by the telephone exchange activates the alerting device on the line. When the called party picks up the handset, the switchhook disconnects the alerting device and connects the audio circuitry to the line. The resulting low resistance now causes DC current to flow through this line, confirming that the called phone is now active. Both phones being active and connected through the exchange, the parties may now converse as long as both phones remain off hook. When a party "hangs up", placing the handset back on the cradle or hook, DC current ceases to flow in that line, signaling the exchange to disconnect the call. Calls to parties beyond the local exchange are carried over "trunk" lines which establish connections between exchanges. In modern telephone networks, fiber-optic cable and digital technology are often employed in such connections. Satellite technology may be used for communication over very long distances. In most telephones, the transmitter and receiver (microphone and speaker) are located in the handset, although in a speakerphone these components may be located in the base or in a separate enclosure. Powered by the line, the transmitter produces an electric current whose voltage varies in response to the sound waves arriving at its diaphragm. The resulting current is transmitted along the telephone line to the local exchange then on to the other phone (via the local exchange or a larger network), where it passes through the coil of the receiver. The varying voltage in the coil produces a corresponding movement of the receiver's diaphragm, reproducing the sound waves present at the transmitter. A Lineman's handset is a telephone designed for testing the telephone network, and may be attached directly to aerial lines and other infrastructure components. History. Credit for inventing the electric telephone remains in dispute. As with other great inventions such as radio, television, light bulb, and computer, there were several inventors who did pioneer experimental work on voice transmission over a wire and improved on each other's ideas. Innocenzo Manzetti, Antonio Meucci, Johann Philipp Reis, Elisha Gray, Alexander Graham Bell, and Thomas Edison, among others, have all been credited with pioneer work on the telephone. A Hungarian engineer, Tivadar Puskás invented the Telephone exchange in 1876. The early history of the telephone is a confusing morass of claim and counterclaim, which was not clarified by the huge mass of lawsuits which hoped to resolve the patent claims of individuals. The Bell and Edison patents, however, were forensically victorious and commercially decisive. Early commercial instruments. Early telephones were technically diverse. Some used a liquid transmitter, some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet, and some were "dynamic" -their diaphragm vibrated a coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. This dynamic kind survived in small numbers through the 20th century in military and maritime applications where its ability to create its own electrical power was crucial. Most, however, used the Edison Berliner carbon transmitter, which was much louder than the other kinds, even though it required an induction coil, actually acting as an impedance matching transformer to make it compatible to the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument. Early telephones were locally powered, using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, "common battery" operation came to dominate, powered by "talk battery" from the telephone exchange over the same wires that carried the voice signals. Early telephones used a single wire for the subscriber's line, with ground return used to complete the circuit (as used in telegraphs). The earliest dynamic telephones also had only one opening for sound, and the user alternately listened and spoke (rather, shouted) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but were more expensive. At first, the benefits of an exchange were not exploited. Telephones instead were leased in pairs to the subscriber, who had to arrange telegraph contractors to construct a line between them, for example between his home and his shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union, already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco, and Bell was not slow in appreciating the potential. Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell, first operated over a second wire, and later over the same wire, but with a condenser (capacitor) in series with the bell coil to allow the AC ringer signal through while still blocking DC (keeping the phone "on hook"). Telephones connected to the earliest Strowger automatic exchanges had seven wires, one for the knife switch, one for each telegraph key, one for the bell, one for the push button and two for speaking. Rural and other telephones that were not on a common battery exchange had a magneto or hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator. In the 1890s a new smaller style of telephone was introduced, packaged in three parts. The transmitter stood on a stand, known as a "candlestick" for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook." Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery and magneto were in a separate "bell box." In phones connected to common battery exchanges, the bell box was installed under a desk, or other out of the way place, since it did not need a battery or magneto. Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular. Disadvantages of single wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long distance telephones, four-wire circuits. Users at the beginning of the 20th century did not place long distance calls from their own telephones but made an appointment to use a special sound proofed long distance telephone booth furnished with the latest technology. What turned out to be the most popular and longest lasting physical style of telephone was introduced in the early 20th century, including Bell's Model 102. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use sat in a cradle in the base unit. The of the Model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled, with energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate enclosure. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1-10 times for each digit, and the hook switch (in the center of the circuit diagram) permanently disconnected the line and the transmitter battery while the handset was on the cradle. After the 1930s, the base also enclosed the bell and induction coil, obviating the old separate bell box. Power was supplied to each subscriber line by central office batteries instead of a local battery, which required periodic service. For the next half century, the network behind the telephone became progressively larger and much more efficient, but after the dial was added the instrument itself changed little until touch tone replaced the dial in the 1960s. Digital telephony. The Public Switched Telephone Network (PSTN) has gradually evolved towards digital telephony which has improved the capacity and quality of the network. End-to-end analog telephone networks were first modified in the early 1960s by upgrading transmission networks with T1 carrier systems. Later technologies such as SONET and fiber optic transmission methods further advanced digital transmission. Although analog carrier systems existed, digital transmission made it possible to significantly increase the number of channels multiplexed on a single transmission medium. While today the end instrument remains analog, the analog signals reaching the aggregation point (Serving Area Interface (SAI) or the central office (CO)) are typically converted to digital signals. Digital loop carriers (DLC) are often used, placing the digital network ever closer to the customer premises, relegating the analog local loop to legacy status. IP telephony. Internet Protocol (IP) telephony (also known as Voice over Internet Protocol, VoIP), is a disruptive technology that is rapidly gaining ground against traditional telephone network technologies. As of January 2005, up to 10% of telephone subscribers in Japan and South Korea have switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing." As of 2006 many VoIP companies offer service to consumers and businesses. IP telephony uses an Internet connection and hardware IP Phones or softphones installed on personal computers to transmit conversations encoded as data packets. In addition to replacing POTS (plain old telephone service), IP telephony services are also competing with mobile phone services by offering free or lower cost connections via WiFi hotspots. VoIP is also used on private networks which may or may not have a connection to the global telephone network. Usage. By the end of 2006, there were a total of nearly 4 billion mobile and fixed-line subscribers and over 1 billion Internet users worldwide. This included 1.27 billion fixed-line subscribers and 2.68 billion mobile subscribers. Telephone operating companies. In some countries, many telephone operating companies (commonly abbreviated to "telco" in American English) are in competition to provide telephone services. Some of them are included in the following list. However, the list only includes facilities based providers and not companies which lease services from facilities based providers in order to serve their customers. |