Archive for the ‘PROTECTIVE COLOURATION’ Tag

BUTTERFLIES AND MOTHS (Part 1 of 2)   Leave a comment

DEFINITIONS:

BUTTERFLY:1 any of various families of lepidopteran insects active in the daytime, having a sucking mouth part, slender body, rope like, knobed antennae, and four broad, usually brightly coloured, membranous wings 2 a person, esp. a woman, thought of as flitting about like a butterfly and being frivolous, fickle, etc. 3 a) short for BUTTERFLY STROKE b) a contest in which each contestant uses a butterfly stroke.

MOTH: 1 any of various families of four-winged, chiefly night-flying lepidopteran insects, similar to the butterflies but generally smaller, less brightly coloured, and not having the antennae knobed.

Lepidoptera, the order of scaly-winged insects including butterflies, moths, and skippers.

To a poet butterflies and moths are like fluttering flowers. Scientists know them as a group of insects that make up the order Lepidoptera, meaning “scale wings.” They are so named because their wings and certain portions of their bodies are covered with a fine dust. Under a microscope the dust is seen to be made up of millions of finely ridged scales that are arranged in overlapping rows. Each scale has a tiny “stem” that fits into a cup like socket. The beautiful colours and markings of the insect are due to the scales, which come in a remarkable variety of colours.

Butterflies and moths look very much alike. The best way to tell them apart is to examine their antennae, or feelers. Butterfly antennae are slender and the ends are rounded into little clubs or knobs. Moth antennae lack these knobs. Many of them look like tiny feathers, and some are threadlike.

Most butterflies fly and feed during the daytime. Moths fly at night. Butterflies rest with their wings held upright over their backs, and moths with their wings outspread. These are not safe rules to follow, however, for some moths are lovers of sunshine and some fold their wings. The honours for beautiful colouration are about evenly divided. The pale green luna moth and the rich reddish brown cecropia moth are as handsome as any of their gay cousins.

Different kinds of butterflies and moths live throughout the world in temperate regions, high in snowy mountains, in deserts, and in hot, steamy jungles. They vary in size from the great Atlas moth of India, which is 10 inches from tip to tip of the spread wings, to the Golden Pygmy of Great Britain, which is only 1/5 inch across. In North America north of Mexico there are 8,000 kinds of moths, but only 700 kinds of butterflies.

Like all insects, the butterflies and moths have three pairs of legs and a body that is divided into three sections head, thorax, and abdomen. On the thorax, or middle section of the body, are two pairs of wings. The pair in front are usually the larger. The scales on the wings contain a pigment that gives the insect some of its colour.

Certain colours, however, and the iridescent shimmer come from the fine ridges on the scales. The ridges break up the light into the various colours of the spectrum. The beautiful blues, for example, are due to the way in which the light strikes the scales.

These insects feed on the nectar of flowers and on other plant liquids. The mouth is a long slender sucking tube. When it is not in use it is coiled up like a delicate watch spring. By uncoiling the tube, the insect probes deep into the flowers and sucks up the nectar. Some kinds of insects have spines on the tip of the tube that tear the plant tissues of ripe fruits and start the juices flowing. Certain kinds have imperfectly developed mouth parts and do not feed at all. Soon after they become adult insects they mate, lay their eggs, and then die.

As the adults visit the flowers in search of nectar, they rub against the stamens and pistils, and so help in the process of pollination. The pronuba moth that pollinates the desert yucca is particularly interesting in this respect.

The Life Cycle Metamorphosis

Butterflies and moths go through a life history known as complete metamorphosis. (The word means “change of form.”) The female lays many eggs. From these hatch tiny larvae called caterpillars. At this time of their lives they become pests, devouring the food plants of man. The female always lays its eggs on the kind of plant that the caterpillars will use for food.

After several moults (skin shedding) the full-grown caterpillar is ready to turn into a pupa. At this stage the butterflies and the moths differ. Butterflies spin a button of silk that adheres to a twig, leaf, or other solid support. They then cling to the button by a sharp spine at the end of the body and moult for the last time. As the old caterpillar skin peels off, there appears a naked pupa called a chrysalis. It is an “insect in the making,” encased in a tough, flexible shell.

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

Some moth caterpillars spin silken cases called cocoons inside which they pass the pupal stage. Others burrow into the ground, about six inches below the surface. There the caterpillar moults for the last time. The pupa is covered with a hard, dark, sticky substance that protects it from cold and moisture and from attacks of other insects.

The time spent in the chrysalis or cocoon varies with the kind of insect and with the time of year. It may be weeks or months. The pupa does not appear to be alive, but marvellous changes are taking place. Most of the organs and other tissues of the caterpillar break down, turning into a semi liquid.

From this material are formed the wings, legs, and other parts of the adult. At last the adult is ready to leave the pupa case. If it is an earth-burrowing kind, the pupa, before it opens, is raised to the surface by means of thrashing movements of the insect on the inside. After the insect has freed itself it is wet and its wings are soft and limp. It slowly fans the wings to pump air into the veins. Gradually the wings expand and harden. In a few hours the adult is ready to fly and to seek a mate. Most adults live from four to six weeks. Some live only a few days, some can live as long as ten months.

Enemies and Defences

Butterflies and moths have many enemies. Birds are among the worst. Various kinds of flies and wasps lay their eggs on or in the bodies of the caterpillars, so the larvae dig in and feed on the tissues.

Sphinx moth (or hawk moth), any of the order Lepidoptera, family Sphingidae; especially the tomato-worm sphinx (Protoparce quinquemaculata); moths are excellent pollinators of plants.

Both caterpillars and adults have ways of defending themselves. Stinging hairs and spines that may be poisonous protect some caterpillars. The woolly bear caterpillars are covered with a fuzz that makes them an unpleasant mouthful. “Frightfulness” is a defence of quite harmless creatures, such as the hickory horned devil with its red horns, the ugly tomato worm, and the caterpillar of the sphinx moth.

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

The monarch butterfly has a foul taste and odour that birds have learned to avoid. The tasty little viceroy butterfly looks exactly like the monarch, only smaller, and for this reason is also avoided by birds. In addition, many butterflies and moths at rest resemble dead leaves or the twigs and bark of trees.

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Posted 2012/03/14 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.