Archive for the ‘INSECT’ Tag

CATERPILLARS   Leave a comment

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DEFINITION: the worm like larva of various insects, esp. of a butterfly or moth [C-] trademark for a tractor equipped on each side with a continuous roller belt over cogged wheels, for moving over rough or muddy ground.

The larvae, or young, of butterflies and moths are called caterpillars, from the Latin catta pilosa, meaning “hairy cat.” Although people usually recognize the hairy kinds, many caterpillars with bare skins are popularly called worms, such as the cabbage worm and army worm

A caterpillar’s body consists of a head followed by 12 or 13 segments. Like all insects, it also has three pairs of permanent or “true” legs one pair on each of the first three segments directly behind the head. These true legs are usually hard, jointed, and tipped with tiny claws, but in a few caterpillars they are not developed. To support the rest of its long body, the caterpillar also has from two to five pairs of soft, thick prolegs that disappear when it changes into a moth or butterfly.

A caterpillar has six eyes like tiny beads on each side of the head, just above the strong upper jaws. It breathes through nine pore like openings, called tracheae, on each side of its body.

When a caterpillar hatches from the egg laid by a female butterfly or moth, it is usually very small. But it grows rapidly and soon gets too large for its skin. Thereupon the old skin splits, and the caterpillar wriggles out of it, revealing a soft new covering. This skin-shedding is called moulting and occurs four or five times. Some caterpillars eat their old skins. The hawk moth caterpillar, one of the largest, may grow 4 inches (10 centimetres) long; the clothes moth caterpillar, one of the smallest, seldom exceeds a quarter of an inch. Some caterpillars may take only a few days before they turn into butterflies or moths, but most last throughout the warm season. A very few may live as long as four years in the caterpillar form before they change.

Cocoon, envelope, often largely of silk, which an insect larva forms around itself.

The change that caterpillars undergo is called metamorphosis. The first step for many moth caterpillars is to build cocoons. They spin them with threads of sticky fluid that flows from an opening in the lower lip and hardens in the air.

Some caterpillars form bags of silk that entirely enclose them. Others roll up a leaf, fastening the edges with the silk. Many of the hairy kinds pad the cocoons with their own hair.

Some caterpillars do not build cocoons. Many of the moth caterpillars take shelter simply by burrowing in the ground or under a stone or fallen leaf. Butterfly caterpillars may suspend themselves from leaves or twigs by their tails, or spin a button of silk on a twig or leaf and hang from it by a silk girdle.

Pupa, quiescent stage between larva and adult in insect metamorphosis.

Whether protected by a cocoon or not, the caterpillar becomes ready to shed its last skin, and in place of it grows a tough flexible shell or case. When this happens it has become a pupa. The moth pupa is usually dull brown and mummy like The butterfly pupa, sometimes called a chrysalis, is shiny and often brilliantly coloured

Inside the pupal, or chrysalids, case, the rudimentary wings and other organs enlarge to make the moth or butterfly. This transformation from the larval to the adult stage may be completed in a few days or take several months.

To grow and prepare for this period of change, caterpillars eat enormously, causing widespread damage to trees, flowers, and crops. The larva of the Polyphemus moth, a species of the American silkworm, has been estimated to eat as much as 86,000 times its own weight during its 56 days as a caterpillar.

Caterpillars are the prey of many birds and insects, especially parasites. To avoid their attacks, caterpillars have various natural protections. Some are coloured to blend with their surroundings. Others have gaudy dots or stripes to make them look fierce or very large. A few give off unpleasant smells, and a very few grow poisonous nettle like hairs.

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Posted 2012/08/19 by Stelios in Education

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WATER BUGS   Leave a comment

 

DEFINITION: any of various hemipteran insects that live in fresh waters, including the back swimmers and the water boatmen.

Even though they breathe air, several kinds of insects can also live underwater and are able to fly, crawl, or swim at will. Called water bugs, such insects belong to the order of true bugs Hemiptera.

One of the most common water bugs is the water boatman, the only water bug that can take flight directly from the water. It usually stays anchored to the bottom feeding on algae and organic debris and keeps a supply of air stored under its wings.

The back swimmer is named for its habit of rowing itself through the water upside down. It stores air in two grooves on its under surface. Each of its three pairs of legs serves a different purpose. The front pair captures small creatures for food; the middle pair holds on to objects; and the long, flat hind pair, fringed with stiff hairs, acts as oars that row with powerful sweeping strokes. Before it can take flight, the back swimmer must crawl onto the land, turn over, and wait for its wings to dry.

The grasping forelegs of the water scorpion resemble scorpion claws, and its scorpion like tail is used as a breathing tube. It seldom swims, preferring to hunt for small fish and insects from a fixed station. A bubble of air trapped underneath sensory hairs on its abdomen imparts stimuli that tell the bug whether it is walking down deeper into the water or heading upward.

The water strider, or pond skater, has a long narrow body and six spidery legs. Unlike the other water bugs, it never ventures underwater. Its underside is covered with a water-repellent coat of hair that keeps it afloat. Its middle legs propel it across the surface, its hind legs act as rudders and brakes, and its short forelegs are used exclusively for catching prey.

American cockroach (or water bug), insect (Periplaneta americana) of the family Blattidae.

The giant water bug is the largest species and can grow up to 4 inches (10 centimetres) long. These bugs have two retractable appendages that, when held together, form a breathing tube. The bugs are strong flyers and formidable hunters. They paralyse their prey by injecting a poison through the beak, and in this manner they can overpower fish twice their own size. The American cockroach (Periplaneta americana), a large insect in the order Orthoptera, is often called water bug.

Water boatmen belong to the family Corixidae; back swimmers, Notonectidae; water scorpions, Nepidae; water striders, Gerridae; giant water bugs, Belostomatidae.

Posted 2012/05/16 by Stelios in Education

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MOSQUITOES   Leave a comment

DEFINITION: any of a large family (Culicidae) of two-winged dipteran insects, the females of which have skin-piercing mouth parts used to extract blood from animals, including humans: some varieties are carriers of certain diseases, as malaria and yellow fever.

More than just annoying insects, some mosquitoes are responsible for transmitting diseases that can result in serious illness and even death. Mosquitoes were once viewed merely as a nuisance because of the itching and irritation that resulted from their bites. In the early 1900s, however, they were recognized as carriers of yellow fever, malaria, and other diseases.

The mosquito is in the family Culicidae and belongs to the same order of insects as flies and gnats the order Diptera and has the same anatomical structure. Its soft body is covered by an exoskeleton (an external supportive covering) and divided into three parts: the head, thorax, and abdomen. It has two narrow wings and a pair of knob-like structures, known as halters, that are present in place of a second pair of wings. Unlike other Diptera, the wings of the mosquito have tiny scales on the veins.

The mosquito’s head is rounded and supported by a slender neck. It has large compound eyes, complex mouth parts, and two antennae, usually divided into 15 segments. The antennae of the male are more feathery in appearance than those of the female. The major body segment behind the head is called the thorax, to which the wings and six legs are attached. The legs are long, slender, and segmented. The final segment of the mosquito’s body is the soft, cylindrical abdomen. It has ten segments, the last ones bearing the openings for the anus and reproductive organs.

Proboscis, snout, trunk, or other tubular organ projecting from the head of an animal.

The most dangerous parts of a mosquito’s anatomy are the female’s mouth parts These are modified into a proboscis for piercing and sucking. The proboscis looks like a single thin tube and is straight in most species. It actually consists of a sheath (the labium) that encloses saw-tipped daggers (the mandibles and maxillae), an injection tube (the hypopharynx), and a sucking tube (formed by closing the labium against the hypopharynx). The construction of the proboscis is ideal for removing blood from beneath the skin of animals. The mouth parts of the male mosquito are modified for feeding on plant juices; male mosquitoes do not bite.

Mosquito Bites

Not all species of mosquitoes suck blood. However in some species a blood meal by the female is essential to the reproductive cycle. In most species the females, like the males, suck nectar and other juices from plants for nourishment. The bloodsucking species feed primarily on mammals or birds, though some mosquitoes will feed on reptiles and amphibians. Some species are particular in their choice of host species, whereas others appear to be less selective. The feeding periods of many types of mosquitoes are restricted to particular times of the day or night.

To obtain a blood meal, a female mosquito selects a likely spot on her victim, brings her labium against it, and begins sawing through the skin with her mandibles and maxillae. Through her hypopharynx she injects saliva into the wound to prevent the blood from clotting so that it flows freely into her labro-hypopharyngeal tube. She then sucks up a supply of blood, stores it in her abdomen, and flies away.

The itching of a mosquito bite is caused primarily by the saliva that has been injected. If the mosquito completes her withdrawal of blood before being driven away, much of the saliva will be removed and the itching may be less severe.

Life Cycle and Habitats

A mosquito’s life cycle is one of complete metamorphosis it consists of four distinct stages: egg, larva, pupa, and adult though the pattern of development may vary between species. The female mosquito typically lays her eggs in standing water, where they float on the surface in a tiny cluster. The eggs may also be deposited singly or attached to vegetation, depending upon the species of mosquito. Some mosquitoes lay their eggs in the vicinity of water rather than directly in water, and the eggs develop when the area becomes flooded.

During warm weather the eggs develop into larvae within two or three days. Mosquito larvae are long, transparent, and constantly wriggling as they move up and down in a water column. They feed on organic matter, including small animals, bacteria, dead plant material, and algae. Some species feed on other mosquito larvae.

Pupa, quiescent stage between larva and adult in insect metamorphosis.

As the larvae grow, they periodically shed their skins (called moulting) in order to accommodate their larger bodies. Mosquito larvae normally moult four times. After the final moult the animal emerges as a pupa. The pupa has an enlarged anterior portion, composed of a head and thorax, and a curved, elongate abdomen. The pupa is aquatic but does not feed. Both the larvae and pupae of most species must come to the water’s surface to breathe. After two or three days the pupa develops into an adult, emerges from its pupal case, and flies away.

Mosquitoes vary in their courtship and mating habits. Many species mate while in flight. The males of some congregate in huge swarms, to which the females are then attracted. The humming sound made by mosquitoes is often a signal to attract mates.

In cooler temperate regions, adult mosquitoes hibernate, emerging in the spring to lay eggs. In some species mating occurs before the approach of winter and the males die, leaving only fertilized females. In others, eggs are laid in the fall and survive the winter without harm to hatch in the spring.

Mosquitoes are found almost everywhere in the world except open ocean areas, the most arid deserts, and the polar regions. Because of their dependence on water for development during their first stages of life, mosquitoes are most abundant in wet regions of the world. Nevertheless, of the more than 150 species of mosquitoes that inhabit the United States, many persist in arid regions of the South west Some species thrive in the extremely cold climates of Canada and Alaska, where vast swarms can sometimes be seen around some of the larger lakes and marshes.

Mosquitoes live in a wide variety of aquatic habitats. Besides lakes, ponds, and marshes, some mosquitoes lay their eggs in small depressions where water has collected temporarily. For example, many species use tree holes or fallen leaves, where water has accumulated after rains. In urban areas, common egg-laying sites for mosquitoes are empty containers that have collected water. Furthermore, mosquitoes are not restricted to fresh water for egg laying salt marshes are also a common habitat of many species.

1902: Cure for yellow fever. Walter Reed was a physician and bacteriologist in the service of the United States Army when he proved that yellow fever is transmitted by mosquito bites. Throughout the 19th century the general assumption was that yellow fever was transmitted by contact with such articles as clothing or bedding touched by someone who had the disease.

A Cuban doctor, Carlos Juan Finlay, theorized that the disease was carried by insects, but he had not been able to prove it. In 1896 an Italian scientist, Giuseppe Sanarelli, isolated the organism Bacillus icteroides from yellow fever patients. Reed, along with physicians James Carroll and Aristides Agramonte, was assigned the task of investigating the bacillus. At the same time, a yellow fever outbreak started in the American military garrison in Havana, Cuba. The three travelled there in the summer of 1900 and, by 1902, proved that mosquitoes were the carriers of the disease.

Shortly afterwards an insect extermination program was undertaken, and Havana was freed of yellow fever within 90 days. Colonel William Crawford Gorgas of the U.S. Army Medical Corps later used Reed’s techniques to rid Panama of yellow fever, making way for the construction of the Panama Canal.

Mosquitoes and Disease

Mosquito-transmitted diseases differ in their geographic distribution, specific causes and effects, and in the types of mosquitoes that transmit them. Yellow fever is caused by a virus that is transmitted primarily by the mosquito species Aedes aegypti, found in tropical and warm temperate regions of Africa and the Americas.

The primary mechanism of transfer of the yellow-fever virus (as well as other disease-causing organisms) is the mosquito bite specifically, when a mosquito bites an infected person and then bites a healthy one. The virus is thus passed from one person to another through the fluids from the mosquito’s mouth. The yellow-fever virus can also be present in other mammals, including monkeys, armadillos, and rodents, and a mosquito can transmit the disease to humans after biting an infected animal. Yellow fever attacks the liver, kidneys, and digestive tract, producing high fever and jaundice, a yellow skin colour from which the disease gets its name. More than half of the victims of yellow fever die within a few days. Those who recover are immune thereafter.

Malaria, disease consisting usually of successive chill, fever, and “intermission” or period of normality.

Malaria is another disease transmitted by mosquitoes. It is caused by microscopic protozoan parasites of the genus Plasmodium. The transmission of malaria is more complicated than that of yellow fever because the parasite must spend a portion of its life cycle inside a mosquito and the other part inside a human. (Yellow fever is dependent on the mosquito only as a transmitting agent.) Malaria is transmitted by mosquitoes in the genus Anopheles.

When an Anopheles mosquito bites a person infected with malaria, it may ingest blood that contains parasites in the sexually reproductive stage, called gametocytes. These gametocytes unite in the mosquito’s digestive tract and produce egg-like cells that burrow into the intestinal wall. They then hatch into free-swimming forms that travel to the mosquito’s salivary glands.

When the mosquito bites an uninfected human, the free-swimming parasites are transmitted to the victim through the mosquito’s saliva. These tiny parasites then enter the victim’s red blood cells and begin to divide to form new parasites. Eventually, the affected blood cells burst, and the parasites are released to enter new blood cells within the host and repeat the process of growth and division.

Within one to two weeks millions of these parasites are being released from burst blood cells, resulting in the characteristic symptoms of malaria: periodic chills and fever. Within ten days to two weeks after the initial infection, a new generation of sexually reproductive parasites develops in the blood of the victim. These parasites produce gametocytes, and victims can then infect any Anopheles mosquito that bites them. In this way the cycle of the disease is perpetuated.

In many areas of the world, including North America, mosquitoes of the genus Culex are transmitters of viral encephalitis (sleeping sickness) and other diseases. Dengue, or “break bone fever,” is a common tropical disease that results in muscular pains and eruptions of the skin. It is transmitted by Aedes and Anopheles mosquitoes.

Filariasis, disease caused by roundworms and transmitted by mosquitoes.

Roundworm, worm of the phylum Aschelminthes and the class Nematoda.

Filariasis, a disease that affects the lymph glands, is caused by parasitic roundworms and is transmitted by several different mosquito species in tropical regions.

Mosquito-transmitted diseases can be controlled through the elimination of mosquitoes or their egg-laying sites, medical treatment of victims, and prevention of mosquito bites through the use of insect repellent or protective clothing. As early as the 1700s South Americans recognized that quinine, an alkaloid obtained from the bark of the cinchona tree, alleviated the symptoms of malaria, though they did not know how the disease was transmitted.

In the late 1800s mosquitoes were implicated in the transmission of yellow fever in Cuba, and in the transmission of malaria in India. The United States Army initiated the first major effort to eradicate a mosquito-transmitted disease when it launched its campaign to quell the Cuban yellow-fever epidemic. Once the relationship between mosquitoes and yellow fever was understood, major projects were undertaken to eliminate the egg-laying sites of the Aedes mosquito. Similar measures were taken in malaria-infested areas of the world.

In addition to eliminating mosquito habitats, large-scale production began of chemical products that would kill mosquitoes or their eggs. Aerial sprays have been developed to kill adult mosquitoes. Toxic chemicals and oil products have been used in aquatic habitats to kill mosquito eggs, larvae, and pupae. Such chemicals must be used with caution because of their potentially damaging environmental effects. Mosquito bites can be prevented effectively with the use of a wide variety of insect repellents.

Assisted by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

Posted 2012/04/29 by Stelios in Education

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MANTIS   Leave a comment

 

DEFINITION: any of an order (Mantodea) of slender, elongated insects that feed on other insects and grasp their prey with stout, spiny forelegs often held up together as if praying.

The predatory mantis is well adapted for catching the living insects on which it feeds. It is often called the praying mantis because of the way it holds its prehensile front legs while waiting to make a kill. The mantis remains motionless or sways gently back and forth, with head raised and front legs outstretched in an apparent attitude of praying.

The lively colouration of the mantis may serve as camouflage or as a lure. It lies in wait among leaves while its large compound eyes search for prey. To better blend with its surroundings, it sometimes spreads its wings like a skirt. When an insect appears, the spiny forelegs jerk out to seize the victim. The prey is caught by the sharp, curved hooks at the end of the mantis’s legs and is held firmly by the rows of spines. Within about one twentieth of a second from the time the mantis has spied its prey, it has retracted its front legs and is feeding on its catch. Although mantises hunt primarily insects, some larger species can overcome small vertebrates such as lizards, frogs, and young birds.

Mantises often devour one another, and it is common for the female to consume the male after, or even during, mating. The female then lays her eggs in a frothy mass, which, when dry, becomes a brownish, papery case. The mantis lives in tropical regions and also in temperate parts of the world. Many scientists classify it in the Dictyoptera order with cockroaches. They call the suborder Mantida from the Greek mantis, meaning “diviner” or “prophet.” Some scientists place the mantis in the separate order Mantodea. Its popular names include mule killer, soothsayer, and devil’s horse.

About 1,500 species are known. The most widespread in Europe and North America is Mantis religiosa. M. religiosa and Tenodera aridifolia sinensis were introduced into North America. The latter is often called Chinese mantis. It is native to many parts of Eastern Asia and is the largest mantis in North America. It grows up to 4 inches (10 centimetres) in length.

Posted 2012/03/08 by Stelios in Education

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FLIES   Leave a comment

DEFINITION:1 a) any dipterous insect; esp., the housefly b) any of several four-winged insects from various orders, as the mayfly or caddis fly 2 a hook covered with feathers, coloured silk, etc. to resemble an insect, used as a lure in fishing: a wet fly drifts below the surface of the water, and a dry fly floats on it 3 Printing a device on a flat bed press for removing and stacking the printed sheets.

While some flies are beneficial to humans as parasites of insect pests or as scavengers and many others are important as plant pollinators, flies are also known to be carriers of such serious diseases as cholera, typhoid, and dysentery. In most species of fly the body and padded feet are covered with bristling hairs and the tongue is coated with sticky glue. Under a powerful microscope, samples of the dust and dirt clinging to these hairs reveal bacteria that cause a wide variety of diseases. Flies get the germs from garbage and sewage. If they touch food later, it too may become contaminated.

Flies can multiply at an incredibly fast rate. Between the months of April and August one female fly could have more than 190 quintillion descendants if all her female offspring and their descendants lived. Although this does not happen, plenty of flies will be produced every summer if only one female in a hundred escapes death long enough to lay eggs. The only effective way to keep down the number of flies is to prevent breeding.

Long exposure to freezing weather kills flies. In cold climates only a few fertile females hibernating in sheltered places survive the winter. Warm weather awakens them and they seek moist spots such as manure piles or garbage in which to lay their eggs.

Maggot, larva of an insect; term most often applied to larva that lives in decaying matter.

The eggs look like tiny white grains of wheat, about 1/20 of an inch (0.13 centimetre) long. The female lays up to 250 eggs in several clusters. Within 24 hours the eggs hatch into white larvae, or maggots. These feed and grow for about five days, then become pupae. Some five days later an adult fly emerges from the pupa case. In two or three days each new female is ready to lay eggs. The entire life cycle takes about two weeks to complete.

The Right Way to Get Rid of Flies

Once flies are established in a locality, they can be suppressed only by eliminating the places in which their eggs can hatch and the maggots can feed. If manure and garbage are removed from a location and destroyed regularly and if garbage cans are kept covered the population of houseflies in that location can be kept to a minimum. If this regular removal schedule is not possible, garbage can be kept in fly-proof containers of sheet metal or screening while awaiting collection. Manure piles can also be treated with suitable chemicals for example, calcium cyanamide and calcium super phosphate (acid phosphate) to keep them from attracting flies.

People can protect themselves from any surviving flies by putting screens on their doors and windows, by swatting, or by applying any of various chemical sprays or dusts, particularly those containing pyrethrum. Insecticides should be used with care to avoid contamination of food, dishes, and utensils.

The Physical Characteristics of Flies

The adult fly is about one-quarter inch (0.64 centimetre) long and about half an inch (1.27 centimetres) across the outspread wings. A thousand adults weigh less than an ounce. Each foot on its three pairs of legs is equipped with claws and two hairy pads called pulvilli. These pads secrete a sticky liquid that enables the fly to cling to almost any surface and run upside down along a ceiling.

A fly has five eyes. Two of these are huge compound structures that cover most of the head. Between these are three tiny simple eyes, set in a triangle. A flys vision, however, is not sharp. It relies more upon its acute sense of smell to locate its food.

The mouth parts are adapted for sucking up liquid food. A long “tongue” has two pads, or lobes, at the end, which act as funnels for drawing in liquid. The fly can also turn soluble foods such as sugar into liquids by spreading saliva on them. Unlike the bloodsucking sand flies, or stable flies (Stomoxys calcitrans), which they resemble, houseflies have no equipment for biting.

Some Relatives of the Housefly

Most two-winged insects (Diptera) are properly called flies. In place of the second pair of wings possessed by bees, dragonflies, and many other insects, true flies have club-shaped balancers (halteres). About 45,000 members of the order Diptera are known; some 11,000 are found in North America.

Stable fly, bloodsucking fly inhabiting stables; often enters houses.

Next to the housefly (Musca domestica), the most widespread and annoying members of the order are probably the mosquitoes. Some of these rank also among the deadly disease carriers. Sand flies, usually found in wet regions, transmit disease by biting. Another dangerous biter is the tsetse fly of central Africa.

Mediterranean fruit fly (or medfly), destructive insect (Ceratitis capitata); attacks fruit, nuts, and vegetables; yellow, black, and white markings; lays as many as 500 eggs in citrus fruits (except lemons and sour limes); larvae tunnel into the flesh of the fruit making it unfit for human consumption; discovered in Florida in 1929; thought to have been eradicated in the United States by 1930; reappeared in 1956 and in the early 1960s and again, in California, in 1981; worldwide quarantine laws were formed because of this pest to regulate the entry of fruits into countries; heavy U.S. infestation in 1981 set off heated controversy between fruit growers and environmentalists; the aerial-spraying program that was finally adopted sparked renewed debates worldwide about the eradication of costly insect pests.

Much damage is done by fruit flies in tropical and semitropical climates. Especially harmful is the Mediterranean fruit fly (Ceratitis capitata). The fruit fly called Drosophila melanogaster has proved extremely useful in studies of heredity. It passes through its life cycle in a few days. The results of selective breeding, of diet, and of other influences can be observed within a short time.

Midges, group of flies belonging to the order Diptera, family Chironomidae; mosquito like in form but more delicate.

Horsefly (also called gadfly), a two-winged fly of the order Diptera, family Tabanidae; usually about 3 times size of housefly; has pointed proboscis; only females suck blood; males sip plant sap or nectar.

Flesh flies breed and lay their eggs in stored meats; bot flies, or heel flies, torment cattle, sheep, and horses; gall gnats damage fruit. Other annoying or vicious flies are the tiny midges, including the “punkies,” or “no-see-ums” (Ceratopogon guttipennis), of the northern woods; the swarming black flies (Simulium hirtipes), which have been known to drive animals into fatal frenzies; horseflies, which also bite humans; and the so-called bee lice, bat ticks, and sheep ticks, which are parasites and so have lost their wings.

More useful members of the order are the syrphus flies, which resemble bumblebees and wasps and destroy plant lice; drone flies, whose larvae live in foul water, eating decaying vegetable matter; and robber flies, which consume other insects. Less-known members of the group are the louse flies, the nimble flies, the humpbacked flies, the March flies, and the false crane flies.

Flies are among the oldest of insects. Their fossil remains are found in rocks of early geologic ages and may also be preserved in ancient amber.

Posted 2012/02/08 by Stelios in Education

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BEETLES (Part 1 of 2)   Leave a comment

 

Giraffe beetle. Also Giraffe weevil.

DEFINITION:1 any of a large order (Coleoptera) of insects, including weevils, with biting mouth parts and hard front wings (elytra ) that cover the membranous hind wings when the hind wings are folded 2 any insect resembling a beetle.

There are more species of beetles than of any other kind of insect. They constitute the largest order of insects Coleoptera which includes almost one third of a million recognized species. About 20 percent of all known species of animals in the world are beetles.

Beetles are found throughout all continents except Antarctica. Although most species are terrestrial, many such as the whirligig, water scavenger, and true water beetles have become adapted to aquatic environments. Some beetles are only about 0.01 inch (0.025 centimetre) long, whereas tropical rhinoceros beetles and Goliath beetles may reach lengths of 4 to 6 inches (10 to 15 centimetres).

Beetles display a remarkable array of colours, forms, and habits. Some are plain black or have brownish patterns that help to camouflage the insects against certain types of wood or soil. Some beetles are brilliant orange, red, or yellow; others are iridescent green or blue or have a metallic sheen. The antennae of some beetles are large and ornate. Some stag beetles have enlarged, hooked mandibles, or lower jaws, that are almost as long as the beetle itself. Male rhinoceros beetles have huge horns projecting over their heads. The shapes of beetles’ bodies vary from round to elongate. Some are flattened; others are domed or cylindrical.

Some beetles are of great significance to humans. Members of the family of beetles known as weevils, or snout beetles, are notorious agricultural pests. They have specialized, elongated heads and down-curved snouts with mouth parts at the end. Some beetles feed on plant materials such as wood, paper, and fabrics. The larvae of some dermestid beetles are destructive pests of clothing and carpets and even of plant and animal specimens in museums.

Many beetles are valuable because they prey on destructive insect pests. Ladybugs, for example, destroy untold numbers of aphids each year and so protect a wide variety of flowers and vegetables. Many other beetles play more subtle but equally important roles in various ecosystems. Dung beetles, or tumble bugs, eat vast quantities of dung in livestock areas. Carrion beetles are scavengers whose larvae feed on dead animals. Many beetles pollinate flowers.

Physical Characteristics

Mandible, from Latin mandere, to chew; term applied to: (1) chewing jaws of insects and other arthropods; (2) the lower jawbone of mammals; (3) the upper or lower part of a bird’s beak.

Like other insects, beetles have three major body segments: the head, with a single pair of antennae and a pair of compound eyes; the thorax, which bears two pairs of wings and three pairs of legs; and the abdomen, where the reproductive organs are housed. Beetles have chewing jaws called mandibles and paired structures known as maxillary and labial palpi (singular, palpus) that are used for feeding or handling food. The bodies of beetles and other insects are covered by a usually hard layer known as the cuticle that supports the internal organs and protects the body. The cuticle is hard because it contains a substance called chitin. Each defined, plate like area of the cuticle is called a sclerite.

A distinctive feature of beetles is their front pair of wings, which are thick, hard, and opaque, without the veins characteristic of most other insect wings. These fore wings, called elytra (singular, elytron), serve as protective wing covers for a second pair of functional wings underneath. The hind wings are membranous and translucent. These are ordinarily used for flying, while the heavy elytra are held out of the way. When the beetle is at rest, the elytra fold over the back and form a straight line down the centre where they meet. Some beetles have shortened wings, and a few species are entirely wingless.

Life Cycle and Behaviour

Like other insects, beetles reproduce sexually by means of internal fertilization. The ovaries of the female and testes of the male are enclosed within the abdomen. In some species, such as the stag beetles, males engage in combat with one another for the right to mate with the females. After mating, the females lay the fertilized eggs in a location suitable for development of the larvae.

Beetles undergo a complete metamorphosis: they develop from egg into active larva into inactive pupa and finally into an adult. The larva, or grub, does not resemble the adult in structure. The pupal stage though soft, pale, and immobile does have the body form of an adult. The life spans of beetles range from a few months in some species to more than four years in others.

Feeding habits. Most beetles feed on living or dead plant materials, but some are scavengers of dead animal matter and some prey on other insects. A few are parasites.

The adults and larvae of a number of beetle species feed on various plant roots, stems, fruits, seeds, and foliage. Some beetles feed only on certain plant species and plant parts, whereas others are less particular in their choice of foods. The adults and larvae of many beetles feed on decaying wood and help break down dead trees and other vegetation in forest habitats.

Some beetles, such as tiger beetles, are voracious predators. Adult tiger beetles search for prey that they can subdue with their powerful mandibles. The larvae are sedentary; they live in small tunnels where they wait to capture passing insects. Water scavenger beetles are predators as larvae but are plant eaters as adults. Some species of beetles have highly selective feeding habits: they may eat only mites, ant larvae, aphids, or zoo plankton

Defences Although most beetles are protected by their heavy armour, some species have developed additional methods of defence Blister beetles secrete an oily, blister-causing substance that deters predators. Beetles may also discourage or avoid predators by making a startling noise (see below, “Light and sound production”), secreting or ejecting an obnoxious fluid, biting, hiding (using their natural colouring as camouflage), or simply fleeing on foot or on wing.

Luminescence, emission of light resulting from causes other than high temperature.

Light and sound production. Many beetles are capable of producing light and sound, primarily for the purposes of attracting a mate or for frightening enemies. The familiar fireflies, or lightning bugs, are beetles that have special light organs on the underside of their abdomens. These beetles usually the males flash their lights rhythmically as a signal that they are ready to mate, and the females return the signal. The kind of signal system used by the two fireflies allows males and females of the same species to recognize and locate one another. Some tropical click beetles have large, luminescent eye spots on the back of the thorax that presumably are also used in courtship.

Many species of beetles make sounds by rubbing together hard parts of their bodies a practice called stridulation. The vibration created by the friction of these parts produces a shrill creaking noise. Beetles may stridulate by rubbing the two elytra together, by rubbing a hind leg against an elytron, or by rubbing the head against the front of the thorax. In some species, even the immature grubs can produce sounds. Although stridulation is often used by adult beetles as a mating signal, its purposes in other instances by juveniles, for example are not fully understood.

A wood-boring beetle known as the death-watch beetle strikes its head against the sides of its burrow as a mating signal. The name death-watch is derived from the superstition that the sound was an omen of death. One explanation is that the ticking sound of a death-watch beetle that had made its burrow in an old piece of furniture was most often heard late at night by someone sitting at a sickbed.

When threatened by a predator, bombardier beetles squirt, with a loud popping sound, an unpleasant-smelling liquid from the rear of their abdomens. The noise and the ejection act together to startle and repel the predator and give the beetle time to make its escape. When click beetles fall on their backs, they right themselves by snapping their bodies in such a way that they are tossed into the air with a loud clicking sound that can startle a predator.

Kinds of Beetles

There are many families of beetles about 135, according to some experts. The beetles discussed below represent a sampling of some of the most commonly known as well as some of the most unusual beetle families in the order Coleoptera.

Tiger beetles and ground beetles are the most common beetles in North America. The fierce, long-legged tiger beetles are fast-running, fast-flying, often brightly coloured beetles that capture and eat other insects. Species of tiger beetles occur throughout the world but are especially abundant in the tropics.

Ground beetle, one of a group of the order Coleoptera, family Carabidae; especially the fiery searcher (Calosoma scrutator), one of the largest beetles; if held carelessly will discharge quantities of “fiery” juice.

Ground beetles are also abundant in most parts of the world. Many species are black and shiny; some are iridescent. Like the tiger beetles, ground beetles have long legs. Some have enlarged, pinching mandibles that are used to capture prey. Many are nocturnal.

True water beetles (also known as diving beetles or predaceous diving beetles) are oval-shaped insects that can swim, dive, and fly. They are found in most freshwater habitats worldwide but are most common in northern temperate regions. The hind pair of legs of the true water beetle are long, flattened, and fringed to provide a greater surface area that helps the insect float. The beetle breathes through spiracles openings on the abdomen just under the tips of the elytra. Before diving, the beetle collects an air bubble beneath its elytra and then breathes from the bubble while it is underwater. It is carnivorous, preying on insects and other aquatic organisms, including fish larger than itself. The larvae of the true water beetles are sometimes called water tigers because of their voracious appetites. True water beetles often fly from one aquatic habitat to another and may be seen around outdoor lights at night.

Whirligig beetles, like the true water beetles, are oval-shaped aquatic predators that can swim, dive, and fly. They are known for their gregarious habits they are usually seen in groups, spinning and whirling around on the surfaces of quiet ponds or lakes. They have distinctive, divided eyes a top pair for seeing above the water’s surface and a bottom pair for seeing below.

Posted 2012/01/25 by Stelios in Education

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PROTECTIVE COLOURATION   Leave a comment

 

Monarch butterfly

DEFINITION: (or colouring) natural colouration of certain organisms allowing them to blend in with their normal environment and escape detection by enemies.

As animals evolved, most of them developed body colours and markings that improved their chances of surviving. This adaptive mechanism, known as protective colouration, may serve any number of functions. Colouring can help protect an animal by making it hard to see. For an animal that spends much of its life trying to avoid dangerous enemies, this is the most useful function. Thus protective colouration is often found among the most helpless creatures those who have little or no other means of defence A white snow hare, for example, blends into its white surroundings and so becomes less visible to predators.

Conversely, colour can help an organism by making it more conspicuous the bright colours of a poisonous snake may warn off intruders, for example. In general, the purpose of protective colouration is to decrease an organism’s visibility or to alter its appearance to other organisms. Sometimes several forms of protective colouration are superimposed on one animal.

Types of Protective Colouration

There are a variety of protective colouration schemes. Each works in a slightly different manner.

Cryptic colouration helps disguise an animal so that it is less visible to predators or prey. One of the most common types of cryptic colouration is background matching, which may take various forms. Many helpless animals have developed colours and markings that match their surroundings in order to hide from predators. Fish eggs and microscopic zoo plankton, for example, are transparent and nearly invisible as they drift in the upper layers of oceans and freshwater lakes. A fawn’s spotted coat camouflages the animal against the speckled forest floor. Some animals attempt to camouflage themselves physically. The decorator crab, for example, cements bits of algae, seaweed, and other ocean debris onto its shell so that it resembles the ocean floor.

Grasshoppers and other insects that live among green plants are often green, and insects that live in the soil, such as ants, are often earth-coloured. The pepper moth has coloured patches that camouflage it against the tree on which it lives. The Sargasso sea dragon lives amid masses of floating algae. The fish is not only coloured to match the plants, but its fins and scales are even shaped like algae. The oriental leaf butterfly, which lives on leaf-littered forest floors, is so intricately and completely camouflaged that its markings include leaf veins and a stem.

Sometimes it is the predator that is camouflaged. Certain predatory fish, for example, blend in with harmless schooling fish and then prey on members of the school. Some species of groupers are camouflaged against the ocean floor as they lie motionless, waiting for prey to swim by.

Certain animals can change their colour in response to different environments or situations. Certain lizards are well known for their ability to match their colour to their surroundings. Varying hares change colours with the season: through the winter their fur is white, and as the snow disappears, their fur turns brown. Thus they remain camouflaged throughout the year.

Another form of cryptic colouration is called disruptive colouration, a scheme in which spots, stripes, or other colour patterns visually break up an animal’s outline. Such patterns may mask the animal’s true shape or make it difficult for a predator to visually resolve it from a colourful or similarly disruptive background. Predators, such as the cheetah, tiger, and leopard, may use their disruptive colouration to avoid being seen. The spots or stripes on their fur allow them to get close to their prey before being observed, improving their chances of getting food. Many fishes and certain birds exhibit disruptive colouration, as do some snakes. The boa constrictor, a tree dweller that grows to several feet in length, is marked with a complex pattern of spots and stripes so complete that a stripe even extends across its eyes. Some patterns of disruptive colouration operate on the same principle to conceal movement. Snakes that are concentrically banded, for example, are difficult to detect when they move between long blades of grass.

A third form of cryptic colouration is counter shading, designed to mask an organism’s three-dimensional form. Many animals, particularly vertebrates, are counter shaded, or shaded lighter on their lower surfaces and darker on their upper surfaces. This colouration counteracts the effects of overhead light, which accentuates an animal’s three-dimensional form by lightening the animal’s upper body and casting its lower body into shadow.

Counter shading gives the body a more uniform darkness and less depth relief so that the animal is less conspicuous.

Many marine animals are counter shaded so that they will not appear as silhouettes when seen from below. A silhouetted organism would be conspicuous and thus attract predators. When viewed from above, counter shaded marine animals blend into the darkness of the sea bottom; when viewed from below, their light lower bodies match the appearance of the water’s surface.

Alluring colouration Some animals are coloured so that a predator’s attention is drawn to a non-vital part of the animal’s body. The lizard known as the blue-tailed skink has a bright blue tail that the animal can shed at will with no harm to itself. Potential predators are attracted to the tail; if they attack the tail, the skink sheds it and darts away unharmed.

Monarch butterfly, insect (Danaus plexippus) of the order Lepidoptera, family Danaidae; breeds on milkweeds.

Warning colouration is intended not to camouflage an organism but to make it more noticeable. Such colouration is found among animals that have natural defences that they use to deter or fend off predators. These defences can take many forms. An animal may simply cause a disagreeable smell (such as a skunk’s odour), or it may actually cause pain (as from bee’s sting) or even death (as from snake’s venom). Many of these animals are brightly coloured, presumably as a warning to potential aggressors. The monarch butterfly, for example which bears a conspicuous pattern of bright orange and black has such a disagreeable taste that a bird will often regurgitate after eating it. Behavioural biologists believe that predatory animals learn to associate such brightly coloured animals with unpleasant or painful experiences and therefore are likely to pass them up as potential prey in favour of a more drab animal. Common warning colours are red, black, and yellow.

Dewlap, in reptile anatomy, a hanging fold of skin under the neck.

Some organisms can change their colour from drab to bright when threatened. The octopus, for example, turns white when agitated and red when it is suddenly frightened. Certain chameleons, usually camouflaged, display a brightly coloured throat sac, or dewlap, as a warning signal to invaders. Furthermore, when a male chameleon enters another’s territory, the dewlap display of the territory’s “owner” serves as a warning to keep out.

Fin, in zoology, external membrane used for propulsion in water.

Other forms of protective colouration Some animals are coloured in such a way that they draw attention to themselves only when they are in motion. Certain birds have light-coloured feathers that are visible only during flight. When the bird comes to rest, these feathers are tucked under darker feathers, so that the bird is once again inconspicuous. Similarly, many fishes have colourful dorsal fins that are extended while the fish is swimming then folded down when the fish is at rest.

In both cases, the animal can use its colouration to perform a sort of disappearing act. It can draw a predator away from a certain area, perhaps a nest of vulnerable offspring, by catching the predator’s attention and moving to another location. If the predator pursues the decoy, the bird or fish can disappear by coming to rest.

Some organisms imitate the protective colouration of others. This phenomenon is known as mimicry. A harmless animal may display the same warning colouration as a dangerous or inedible one in order to deceive predators into reacting as though the benign animal had the same defences as its model. In other cases, several noxious species will share a similar warning colouration so that potential predators will generalize and avoid all species with such colouring

Evolution of Protective Colouration

The intricate schemes of protective colouration are the results of long-term evolution. Through aeons of adaptive changes, certain organisms have acquired patterns of colouration that have helped them survive and reproduce.

Effective forms of protective colouration have been passed on to following generations. The processes of mutation, natural selection, and reproduction have combined to produce many organisms with colourations that are fine-tuned to their individual environments and their individual protective needs.

Assisted by Elliot Mitchell, science teacher, Latin School of Chicago.