Archive for the ‘ANT’ Tag

TERMITES   Leave a comment

DEFINITION: any of an order (Isoptera) of pale-coloured social insects having a soft body and living in colonies composed of winged forms that mate and wingless workers and soldiers that are usually sterile or immature: they are very destructive to wooden structures and are found in the temperate zones and esp. in the tropics.

Although they are closely related to cockroaches, termites are sometimes called “white ants” because their general appearance and social organization are like those of the ants. Termites, however, are distinguished from ants by their soft bodies and lighter colour Ants have hard bodies and are usually dark. Furthermore, the termite’s mid body segment, or thorax, is broadly attached to the rear segment, or abdomen, whereas ants have a constriction where the thorax joins the abdomen. Termites belong to the insect order Isoptera.

Ground Nesters

More than 2,000 species of termite have been described, most of which live in the tropics. More than 40 species live in the United States. A typical colony lives underground in a damp, chamber like nest. The colony is organized into a caste system with four different adult forms: royalty, nobility, soldiers, and workers. The royalty consists of the kings and queens, which carry on the work of reproduction. They have well-developed wings and eyes. The kings are usually smaller than the queens, which may reach a length of 4.3 inches (11 centimetres) in some species.

Once a year pairs of young kings and queens depart from the parent nest, leaving the ruling king and queen behind. Each pair starts a new colony nearby. They then shed their wings. Within a short time the young queens may begin laying eggs at the rate of 3,000 to 5,000 a day. The nobility consists of wingless or short-winged adults. They take over the work of reproduction if a king or queen should die.

The soldiers and workers grey-white, wingless, usually blind, and less than 0.4 inch (1 centimetre) long are the most populous members of the colony. Both male and female soldiers and workers are sterile, so they cannot reproduce. The soldiers, which have large heads and jaws, guard the nest against insect enemies, chiefly ants. The workers keep the colony supplied with food, and they actually feed the queens, soldiers, and young termites.

Cellulose, complex carbohydrate consisting of 3,000 or more glucose units; basic structural component of plant cell walls; 90% of cotton and 50% of wood is cellulose; most abundant of all naturally occurring organic compounds; indigestible by humans; can be digested by herbivores, such as cows and horses, because they retain it long enough for digestion by micro-organisms present in their digestive systems; also digestible by termites; processed to produce papers and fibres; chemically modified to yield plastics, photographic film, and rayon; other derivatives used as adhesives, explosives, thickening agents, and in moisture-proof coatings.

Termites feed primarily on wood fibre, or cellulose, which they get from dead trees, rotting plant material in the soil, fence posts, house timbers, or furniture. Although some kinds of termites can destroy human dwellings, they serve a vital function in the food web by recycling the nutrients in dead wood so that the nutrients can be used by bacteria and plants.

Cellulose is indigestible to nearly all animals, large or small, including termites. The termite workers, however, have formed a remarkable partnership, or symbiosis, with micro-organisms called protozoans. The workers harbour the protozoans in their intestines. As they chew and swallow the wood fibre, the protozoans transform it into a product that termites can digest. Soldiers also have symbiotic protozoa, and they can digest cellulose after the workers have chewed it up for them. The soldiers’ enormous fighting jaws prevent them from gathering this fibre for themselves. Royalty and nobility lack protozoans and are fed on digested cellulose secreted by workers.

Worker termites may eat wood that is above ground by entering the wood where the timbers touch the ground. If a house has a stone foundation, the termites may build tubular, earthen passages over the foundation and up to the house beams. The termites thus maintain their contact with the ground and the necessary moisture. Under a porch they may erect towers more than 1 foot (0.3 meter) high to reach the wooden floor. Once inside the woodwork of a building, they tunnel in all directions, with no openings showing on the surface. Houses may be inspected for signs of termite problems by searching for hollow timbers, termite nests at the base of wood, or the insects themselves. Unfortunately, the first sign of their presence may be the collapse of a wall or some other wooden structure. Termites work in large numbers as many as 4,000 have been counted in 1 cubic foot (0.03 cubic meter) of wood.

To rid an area of termites would require the destruction of all the nests. It is more practical to “insulate” a building against the insects by treating woodwork with chemicals or by covering all possible points of attack with metal.

Ground-nesting termite, a termite (Reticulitermes flavipes) of the order Isoptera.

The scientific name of the common ground-nesting termite of eastern North America is Reticulitermes flavipes. Besides the ground-nesting termites there are dry wood, damp wood, and powder post termites. Many of these species live not in soil but in the wood that they attack. They do not require moisture from the soil because they can conserve water in their bodies. These termites can also be eliminated from infested sites by the use of chemicals.

Mound Builders

Mound-building termites live in South America, Africa, and Australia. Their brown mounds, or termitaries, often crowd together in a close group of slender towers. They are built of saliva-soaked soil particles and are as hard as concrete. Some termitaries are decades old and are more than 23 feet (7 meters) high and 43 feet (13 meters) wide at the base. The bases of some termitaries are oval, with the long axis pointing north and south, presumably so that the sun can reach both of the broad outside walls and keep them warm and dry.

Inside the walls of each termitary the social order is the same as that of the ground-nesting termites. The king and queen occupy the royal chamber. The king is small, but the queen is large and may carry as many as 75,000 eggs. Some of the larger queens lay one egg each second, 24 hours a day, during their reproductive life, which may last up to 10 years. After being laid the eggs are taken by nurses, washed with saliva to prevent mould, then carried to the hatchery, which is kept warm by decaying vegetation.

The sightless soldiers, with their strong scissors-like mandibles, guard every turn of the galleries inside the nest. Other soldiers, equipped with tough “helmets” to check any onrush of ants, guard the entrances from the outside world. The soldiers of some species have snouts through which they spray a sticky liquid that entangles the legs of their enemies and that also stupefies them. The worker caste gathers bits of wood to feed the entire community. Some termite colonies grow small mushrooms in fungus gardens for their food. Some have community “cows” small beetles called termitophiles that live only in termite nests and secrete a fluid relished by the termites.

Assisted by J. Whitfield Gibbons

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Posted 2012/09/08 by Stelios in Education

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BEES (Part 1 of 3)   Leave a comment

 

DEFINITION: any of a large super family (Apoidea) of broad-bodied, four-winged, hairy hymenopteran insects that gather pollen and nectar, have biting as well as sucking mouth parts, and often live in organized colonies; esp., the honeybee.

People have known ever since ancient times that the insects called bees make delicious honey from the nectar of flowers. There are more than 20,000 species of bees, and they are found all over the world except in Antarctica. Most people throughout the world recognize honeybees, and people in temperate regions know bumblebees as well (in some places they are called humble-bees). In Central America and South America many persons are familiar with tropical sting-less bees.

Physical Characteristics

Bees are flying insects that are related to wasps, hornets, and ants. Most bees have short, thick bodies covered with hair and, like all insects, six legs and three body parts: head, thorax, and abdomen. The thorax in turn has three segments, each with a pair of legs. A tiny waist connects the thorax and abdomen.

Ordinarily, most bees fly about 12 1/2 miles (20 kilometres) per hour, but they can fly much faster. They have two pairs of wings. One pair is attached to each of the last two segments of the thorax, but front and back wings are joined so that they may look like only one. The rapid movements of the wings make a humming sound in flight.

With three single eyes on top of their heads and two huge, helmet-like compound eyes, bees can see colour, pattern, and movement. The many facets of their compound eyes give them a total image in a mosaic of dots. Bees see all colours humans do except red, and they see ultraviolet, which humans cannot. Ultraviolet is often reflected by red flowers. Bees can also detect the polarization of light, which humans cannot. For example, in a blue sky polarized light forms a distinctive pattern around the sun, and even when the sun is behind the clouds bees can perceive that pattern and orient themselves to it.

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.

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

On the lower part of their heads bees have biting jaws (mandibles) and a mouth-tongue proboscis, of several parts, which they use for sucking and lapping. Bees can distinguish very slight differences in sweet and bitter tastes, and they can also identify sour and salty tastes. Their front legs and feelers (antennae), as well as their proboscises are used for tasting. The antennae are primarily for sensing fragrances: bees find the perfumes of flowers even more enticing than their colours and shapes. Bees have no ears, but they can sense the vibrations of the surfaces upon which they alight.

The largest bees, which include some of the leaf cutter and carpenter varieties, may be up to about 1 1/2 inches (4 centimetres) long. Bumblebees are larger than most about 1 inch (2.5 centimetres) long. Honeybees range from about 1/2 inch to 1 inch (1.3 to 2.5 centimetres) long, depending upon the species. Some of the small leaf cutter bees are only 2/5 inch (1 centimetre) long, and sweat bees are 3/10 inch (0.7 centimetre) long. The tiniest species, the mosquito bees, may be only 3/50 inch (0.2 centimetre) long.

Most bees have black bodies, many with yellow or brown markings. Others have yellow, red, brown, and metallic green or blue bodies, some with brilliant metallic red or purple markings. Honeybees are dark brown with dark yellow stripes. Bumblebees are usually black with wide yellow or orange bands.

Food from Flowers

Honeycomb, a waxy many-celled structure made by bees for holding honey.

Depending upon its size and the length of its proboscis, a bee can enter many kinds of blossoms to sip nectar, the sweet liquid secreted by the flower’s glands. The bumblebee has a long proboscis and so is better equipped than many others for taking nectar from red clover, the flowers of which are made up of clusters of tubular blossoms. The nectar is carried in a special part of the bee’s stomach. During the digestive process enzymes are added, and the nectar becomes honey. Later it is regurgitated into the cells of the comb within the hive. When full, the cells are left until the honey has dried and thickened to the right consistency. Then the bees cap the cells with wax to preserve the honey and prevent further drying.

Pollen gathered from flowers clings to special branched or feathered hairs on the bee’s body. After pollen has accumulated, the bee brushes it off and moulds it into tiny balls mixed with honey from its mouth. This is beebread, the food of the young bees. The bee pushes these pellets into a particular formation of hairs or bristles for carrying them back to the nest. Honeybees have a pollen basket of stiff hairs on their hind legs. Leaf cutting bees have a dense brush on the underside of the abdomen.

Pollination

Fascinated by both colour and shape, bees show a strong preference for flowers with elaborate embellishments and respond eagerly to patterns of colour, particularly of yellow, blue, and ultraviolet. A more deeply shaded pattern is present near the centre of some blossoms. This clearly marked area acts as a carpet of colour to guide the bee to the nectar.

Snapdragon, herbaceous plants composing the genus Antirrhinum of the figwort family with showy white, yellow, pink, or red flowers; lower lip of large tubular corolla snaps shut if opened; many beautiful garden varieties have been derived from Antirrhinum majus.

The liplike petals of many flowers provide a place where a bee can land before entering. When a bumblebee alights on the lip of a snapdragon, the bumblebee’s weight, which is greater than that of most bees, opens the flower’s mouth, letting the bee enter the inner chamber to sip the nectar.

As bees go from one blossom to another, much of the pollen that clings to their bodies is transferred to the flowers of other plants of the same species, pollinating, or fertilizing, them. This permits the plants to produce their fruits and seeds. The bees’ greatest value by far is as pollinators of plants.

The Sting and Other Defences

A female bee has an egg-laying device (ovipositor) located at the end of its abdomen; the ovipositor also serves as a weapon and can inflict a painful sting. The bee’s sting has no food-capturing function. It has come to be used for defence against animals and humans that raid their honeycombs, and against robber bees and parasitic bees attempting to enter their nests.

Most bees can sting many times, but a honeybee worker has a tiny, hook-shaped barb that is caught inside the victim. This bee cannot fly away without tearing out its ovipositor and some internal organs a fatal injury. After the dying bee has flown away, its poison sac and the muscles left attached to the ovipositor keep pumping poison into the victim. As soon as possible the sting should be removed without squeezing the poison sac.

Africanised honeybees, also called killer bees, are particularly aggressive. They are descended from African bees that were imported into Brazil in 1956. The imported bees escaped in 1957 and began to mate with European honeybees the kind found in most hives. Although the sting of one Africanised bee is no more dangerous than that of a European honeybee, the Africanised bees release a chemical when they attack that signals other bees to come and join the attack. These bees may swarm over great distances in pursuit of a raider of their hives, and they have been known to attack in such numbers as to kill farm animals and humans. Since 1957 they have been moving steadily northward, and the first swarm entered the United States in October 1990.

Bumblebees sting when their nest is disturbed, but they are not easily aroused when they are gathering nectar. Sweat bees, attracted by perspiration, may alight on a person’s skin in summer. Their stings are sharp but not as painful as those of the honeybee.

Tropical sting-less bees defend their colony by crawling into the eyes, ears, and nose of an animal or under the clothing of a human raider. They bite, and create unpleasant sensations because of their sheer numbers. Some species secrete a caustic chemical that burns the skin.

Posted 2012/02/15 by Stelios in Education

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WASPS – any of various families of winged hymenopteran insects   Leave a comment

Most people think of wasps only as bugs with bad tempers and sharp stings. Actually, wasps exhibit remarkably sophisticated behaviour and are often helpful, especially to farmers, because they help to check the population of other insects that may be harmful to crops. The many species that feed on nectar travel from flower to flower just as bees do and so are significant as pollinators of various plants. In spite of their reputation, wasps sting humans only when threatened, frightened, or provoked.

Wasps are members of the insect order Hymenoptera, which includes ants, bees, and sawflies. Besides the large and commonly known kinds of wasps, there are a wide variety of small and solitary species. In all, wasps comprise about one-third of the more than 100,000 species in the order.

Wasps characteristically have two pairs of clear, membranous wings, the back pair slightly smaller than the front. Most wasps are strong flyers, but some, such as the female velvet ants, are flightless. As with other insects, the wings and six legs are attached to the middle segment of the body, the thorax. The rear segment, the abdomen, is generally elongated, and the connection between the thorax and abdomen is usually quite narrow. The head has a pair of compound eyes, which form multiple images, and usually three simple eyes, which form single images. The antennae are straight, flexible, and usually composed of 12 or 13 segments. The mouth parts consist of mandibles and maxillae. Mandibles are great, short jaws that are toothed at the tips. Maxillae are smaller mouth parts located behind the mandibles.

Not all species of wasps have stingers. Furthermore, because the stinger is actually a modified ovipositor (a structure used for laying eggs), it is present only in female wasps. The stinger is usually tucked into the tip of the female’s abdomen and is connected to a venom gland. When the wasp stings its insect prey, it injects a poisonous substance that paralyses or kills the victim. Some wasp species that do not sting use their ovipositors to inject their eggs directly into a host insect or plant.

Most wasps are predatory and feed primarily on other insects, including other members of their own order. Their larvae are frequently voracious parasites that eat insects or spiders supplied by the mother wasp. This habit of acquiring animal food to feed their larvae distinguishes these wasps from bees, which nourish their young on plant material.

Wasps may be divided into two groups the social wasps and the solitary wasps though there are species that exhibit characteristics of both.

Social Wasps

Social insects, those living in communities and having differentiated forms or castes, as queens, workers, drones.

These species live in colonies in which responsibilities are divided between three castes: a fertilized female or queen, female workers (usually sterile), and fertile males. In the temperate regions of the world the general reproductive pattern of these wasps begins in the spring when a single queen begins to build a nest in which to lay her eggs. As she builds, other females of the same species join her but remain only as assistants that aid in the construction, food gathering, and care of the larvae. Generally only the original queen is allowed to lay eggs, and she will eat any eggs laid by the accessory females. When the first larvae have become adults, the queen drives away the other females.

This first generation of young is composed exclusively of females whose ovaries are non-functional and who act strictly as workers. They continue with the construction of the nest, care for the next generation of young, forage for food, and feed the queen and each other. It is the second generation of young, emerging in the autumn, that produces the fertile males and females. Shortly thereafter the males are driven from the nest and the young females follow them to be inseminated. Eventually all members of the colony die except for the fertilized queens. They hibernate through the winter, and in spring begin the reproductive cycle again. In the tropics some of the social wasps do not die seasonally, so colonies may persist for several years.

Paper wasp, insect (Polistes fuscatus) of the order Hymenoptera, family Vespidae.

Among the more common social wasps in North America are the hornets and yellow jackets. The female workers of these species, though small, are fiercely protective and highly venomous. Bronze coloured paper wasps are another variety of social wasp. These species and a number of others build their nests from a paper like material made by the wasps themselves. The “paper” consists of plant materials that are chewed and regurgitated by the wasps then stroked into fine strips and glued together.

The hornets are known to build extensive, elaborate nests. They select a location in the branches of shrubbery, in hollow trees, under the frameworks of houses, or in subterranean sites such as mouse nests. First the queen attaches one hexagonal cell to the ceiling by a little stalk, with the opening down. After a week she has created a small plate of five to ten cells. Later, when the numerous workers join in the construction, the nest grows to an impressive size. In subterranean nests the hole may be considerably enlarged to permit expansion. New levels of the comb are added progressively from the top down, with pillars connecting the different tiers. Then the combs are completely covered by a balloon like envelope that may be either elastic or brittle. The single opening, for entrance and exit, is located at the bottom; it also serves as the ventilation hole. The multi-layered envelope both protects the hive and assists in temperature regulation.

Temperature, degree of hotness or coldness measured on a definite scale.

Wasps also are capable of regulating the temperature of the nest themselves. Even on autumn nights when the outside temperature falls to 50 F (10 C), the interior of the nest stays within a half degree of 86 F (30 C). The females accomplish this by moving their flight muscles while keeping their wings motionless, thereby generating heat from their metabolic activity to warm the nest. If, on hot summer days, the outside temperature rises above the 86 F (30 C) optimum for the wasps and their brood, the workers cool the nest by bringing in water and causing it to evaporate by beating their wings.

Solitary Wasps

Most wasps are solitary and harmless. They do not live in colonies, and most do not defend their nests from intruders. Usually these species lay their eggs inside single cells constructed to house the larva and its store of food through the pupation stage (the cocoon phase before the larva emerges as a full adult). Most female wasps lay in a supply of paralysed insects for the larvae to feed upon when they hatch, then seal the entrance to the cell. The insect meals are usually preserved alive to ensure a supply of fresh food for the larvae. Some reports indicate that, if uneaten, these victims may remain paralysed and helpless, but still alive, for as long as four months. After the larva has consumed its ready-made meal, it pupates, and emerges the following summer as a full adult.

Many species of solitary wasps are unusually selective in their choice of the prey they feed their larvae. They may specialize in hunting one particular victim to the exclusion of all others. Surprisingly enough, it seems to make no difference to the larvae they have been known to thrive on an artificial diet. Nevertheless the females continue their single-minded pursuits. One species even hunts only winged female ants, ignoring the many female ants that have already discarded their wings. Naturalists are still at a loss to explain why this wasp then bites off the wings of the captured ants before placing them in her nest.

Representatives of almost all insect orders appear on this select list of prey of the various wasp species. For example, the ensign wasps hunt only cockroaches; the mud daubers only spiders; cicada killers only cicadas; digger wasps only beetle larvae; potter wasps only caterpillars; and the particular bee-killer wasp pursues only the honeybee.

Gall (or gall nut), abnormal growth on leaves, stems, buds, flowers, or roots of plants caused by various parasites, especially insects and mites, and more rarely by nematodes, bacteria, fungi, slime moulds, and algae; found on almost all forms of plant life, but especially common on oak trees, willows, roses, and goldenrod.

The gall wasps, which lay their eggs in the tissues of plants, select not only a particular species of tree or shrub, but also particular parts on the host plant. The developing larvae are a major source of plant galls, or tissue swellings. Those plants commonly affected include the oak trees and rose plants. However, though the galls are unsightly, they ordinarily do little harm to the plants because they are relatively small and localized.

Some species of solitary wasps prefer not to expend their energy on nest building, hunting, and child care. They are noted for smuggling their eggs into the cells of other wasps, a practice called brood parasitism. The cuckoo wasps, small, flying wasps with bright metallic green or blue colouring, are among the most beautiful of the order Hymenoptera, and they are all parasites. The female usually lays her eggs inside the nests of bees, thread-waisted wasps, or yellow jackets. If she is caught in the act and attacked, she rolls herself into a ball to protect herself from the nest owner’s stings. Finally she is thrown from the nest and left for dead; she emerges unscathed. If the cuckoo wasp is successful in laying her egg, the host does not notice the deception. When the cuckoo wasp larva hatches, it eats the host’s larvae along with any food stored for them. It then spends the winter as a pupa and emerges in the spring as an adult.

Another group of parasitic wasps, the velvet ants, are common in most parts of the world, particularly in the Southern and South western United States. Despite their name, the velvet ants are not true ants. They were mistakenly named after the females, which are wingless. Many members of the species are brightly coloured often scarlet or yellow. The largest members of the velvet ants, the so-called cow killers, are bright orange or red. They reach lengths of up to 1 inch (2.5 centimetres) and have stingers that are almost half again the length of the body. Like the cuckoo wasps, the velvet ant is a parasite that lays its eggs in the nests of other insects. Although the velvet ants generally select other wasps or bumblebees to act as hosts, a variety of other insects have been identified as their hosts, including mud daubers in North America, bumblebees in Europe, and tsetse flies in Africa.

Wasps exhibit a wide range of behaviours, not all easily categorized. Some non parasitic solitary wasps check on their larvae regularly, bringing them fresh stores of food whenever necessary and sealing the nest only when the larvae have pupated. Others lay their eggs on temporarily paralysed hosts, then leave the young to fend for themselves. In the latter case the unfortunate host, having regained the use of its limbs, continues about its business undaunted until the larvae hatch and begin to consume its body. Another species of wasp exhibits a highly unusual form of social parasitism. The parasitic queen invades the nest of a colony of social wasps, demotes the queen to worker, and assumes her throne. In this case the former queen lays no more eggs, the host wasps care for the offspring of the conqueror, and the host species dies out without descendants.

Wasps are found throughout the world on every continent except Antarctica and on all major islands. Several thousand species of wasps occur in North America, but wasps are most numerous and their species most diverse in tropical areas. Some of the parasitic wasps are the smallest insects in the world, reaching maximum lengths of less than 0.008 inch (0.02 centimetre). The largest wasps reach lengths of more than 2 1/4 inches (6 centimetres).

The stinging wasps belong to the suborder Apocrita of the order Hymenoptera, the non stinging wasps to the suborder Symphyta. The majority of the social wasps belong to the family Vespidae, and can be distinguished from most other wasps by the way they fold their wings like a closed fan along their back when at rest. Many members of the Vespidae are black with bright yellow or white cross bands or other markings. Hornets and yellow jackets belong to the subfamily Vespinae, whose members are widespread throughout North America, Northern Africa, Europe, and Asia. The paper wasps belong to the subfamily Polistinae, which contains more than 150 species throughout the world.

The families of solitary wasps are numerous and varied. The ensign wasps belong to the family Evaniidae, the mud daubers and cicada killers to the family Sphecidae, digger wasps to the family Scoliidae, and potter wasps to the subfamily Eumeninae of the family Vespidae. Other wasp families include the Cynipidae (gall wasps), Chrysididae (cuckoo wasps), and Mutillidae (velvet ants).

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

Posted 2012/01/12 by Stelios in Education

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ANIMAL BEHAVIOUR (Part 2 of 3)   Leave a comment

Orienting Behaviour

An animal orients by adjusting its posture and position in space. It does so in relation to the source of different forms of energy in its environment. These forms include light, heat, and chemicals in the air or water, pressure, electric current, air or water currents, gravity, radiation, and magnetic fields.

Tropism, involuntary turning of a cell or organism in response to a stimulus.

Orienting behaviour may take the form of a tropism an action in which the animal simply orients its body toward or away from the source of energy without changing location. Plants can also respond in this way. However, the orienting response may take the form of a taxis a movement toward or away from the source of energy by swimming, flying, or locomotion. As a rule, only animals are capable of such responses. Still another type of orienting response is called a kinesics an increase or decrease in an animal’s activity, but in no particular direction.

Prefixes are usually added to the root words tropism, taxis, and kinesics to indicate the kind of energy to which the organism is responding. For example, geotropism is response to gravity; photo taxis, response to light. Prefixes may also indicate the type of response made. Thus klinokinesis refers to turning activities. In addition, the direction or intensity of a response may be described as positive, if directed toward a stimulus, or negative, if directed away from it.

Orientation makes it possible for an animal to feed, to exhibit social behaviour, and to avoid obstacles and barriers. Some organisms, such as the bat, use sonar reflected sound to locate prey and to avoid obstacles. Some fish can navigate through tight crevices by detecting changes in their electric field. Electronic instruments enable researchers to detect and record the sound frequencies and electricity emitted by different species.

When foraging for food, the honeybee orients to the odour of flowers and the polarization of light. It also responds to cues from the sun’s position off the horizon. This type of activity is called sun compass orientation. On returning to the hive the bee performs certain “dances” a variety of motor patterns that vary with the distance and direction of the food. These dances stimulate the other bees to travel the path of the returning bee.

Fish and birds also exhibit compass orientation when homing or migrating. However, scientists are not sure that animals navigate in the same way as man. When humans navigate, they use such instruments as the sextant to find the altitude of the sun and stars and a chronometer for timekeeping. It has not yet been demonstrated that homing and migrating animals can “shoot an azimuth” and “tell time.”

Some animals are known to return to the areas where they were born or spawned. The salmon, for example, upon reaching sexual maturity responds to the chemical characteristics of the stream in which it was spawned. The hormonal changes associated with sexual maturity are a cause of this new sensitivity. The stickleback moves from salty to brackish water to reproduce. Its behaviour is related to endocrine gland responses to seasonal fluctuations in light. Similar hormonal changes in birds lead to migration and reproduction. These cyclic changes in behaviour due to hormonal regulation are considered evidence of a chronometer that might enable migrating or homing animals to correlate changes in visual cues during compass orientation with changes in internal rhythms and thus make navigation possible.

Social Behaviour

All living things relate to other members of their species. In an amoeba, the relationship occurs only during the short time it takes the animal to split into two animals. In other species, such as the social insects, the relationship is so necessary that they cannot survive as individuals. This is true also of humans, who are dependent on others until they reach maturity. Social organization of some kind is common to all animals. However, the type of organization varies with the nervous system of the species. And in true social organization, animals of the same species react to each other.

Con-specifics, or animals of the same species, may at times be close to each other without exhibiting social behaviour For example, mollusc larvae may respond to changes in the intensity of light by swimming to the water surface. The resultant grouping, called an aggregation, stems from a common response to a physical aspect of the environment. But a response is truly social only when it is a response to visual, chemical, auditory, or other stimuli emanating from a con-specific As a result of such stimuli, animals may approach each other to form a bond or to fight. Although dissimilar, both reactions are examples of social behaviour

Goby, any of numerous, widely distributed, spiny-finned fishes constituting family Gobiidae, having wide, flat head, large mouth, and ventral fins often united in funnel-shaped disk.

The type of bond formed by con-specifics is a measure of their nervous and hormonal systems. Organisms with relatively simple systems may respond to each other only as long as they give off attractive or offensive stimuli. For example, a worm will approach another worm during the reproductive state because certain chemicals are released. Once mating has occurred, they have nothing further to do with each other. A goby will remain near its eggs only as long as the hormonal state of the fish and the chemical and visual features of the eggs remain the same. Once the fry, or young, hatch, the fish responds to them as it would toward any small fish and tries to eat them. The goby does not recognize the fry as its own offspring.

Although orientation, changing hormonal levels, and other processes play a part, social bonding depends primarily on a mutual exchange of stimulation and food between animals. The give-and-take stimulation of a pair or a group is fundamental to the organization of social groups.

The Army Ant Colony – An Example of a Social Group

An army ant colony consists of many thousands of workers and a queen. The queen is capable of laying large batches of infertile eggs when she is fed sufficiently. These eggs hatch into workers, females incapable of sexual reproduction. However, at a certain stage of the queen’s development she produces a brood of males and females capable of reproducing and starting new colonies.

The colony has a two-phase cycle of activity. The nomadic phase lasts about 18 days. By late afternoon or early evening, the larger workers cluster and leave the bivouac area where they spent the previous night. They move out over many yards in the area around the bivouac. As they crawl, they lay a chemical trail. Other ants in the colony travel over the trail, and as the trail becomes more frequently travelled the concentration of chemical stimuli on it becomes stronger. The entire colony, queen and all, eventually move out from the bivouac along the trail. The ants range over large areas, preying on other insects and their young.

Army ants take in considerable food during the nomadic phase. The queen receives a good deal of it. She does not usually forage but is able to feed on the food brought back by medium-size workers. They return to the bivouac to lick the queen for the highly attractive chemicals she exudes. Chemicals that attract or repel con-specifics and heterospecifics (members of other species) are called pheromones. The exchanges of food and secretions between the queen and the workers produce a strong social bond that aids in keeping the colony together. The queen’s increased food intake enables her to lay a batch of eggs. However, this affects her relationship with the workers. She becomes less stimulating to them, and their foraging, therefore, begins to decrease. Now the colony enters the other phase of its cycle the statuary phase. The number, frequency, distance, and area of foraging decreases considerably. The level of the entire colony’s activity drops to a minimum.

After about 21 days the eggs hatch, and the larvae emerge. These squirming, active young are an intense source of stimulation to the workers. The workers are driven out of the bivouac and the nomadic phase starts again. They are now attracted by the pheromones of the larvae and the queen. When the workers return from foraging, they drop their food and feel and handle the larvae with their antennae and legs. As a result of this excitation, the number and frequency of raids again increase. The colony travels great distances, the larvae are fed, and the queen is overfed. At this point, the colony consists of the queen, workers, and larvae.

About 18 days after the eggs have hatched, the larvae enclose themselves in cocoons and become pupae. At about the same time, the queen lays her next batch of eggs. Now the colony consists of the queen, workers, pupae, and developing eggs. However, the pupae and the eggs offer little stimulation for the workers, and the statuary slowdown begins. But the queen continues to secrete pheromones that socially bind the colony.

Dominance

In communities of certain animals the ruling, or dominant, animal is the largest, strongest, or most aggressive and thereby exerts the most influence on the other animals in the group. The dominant animal enjoys the greatest and most preferential access to members of the opposite sex and control of the best territory for feeding and breeding. Many groups of animals, most notably baboons, birds, foxes, lions, and crocodiles, establish dominance hierarchies. The best-known example is the pecking order of chickens. Flock members are arranged on the “rungs” of a social ladder, with each chicken superior to those below and subordinate to those above. The top animal has primary access to the necessities of life, such as the best food, mates, and living quarters. Submissive animals are left with less-desirable food, mates, and living quarters. Such animals may even be expected to groom dominant members and to help care for the offspring of more dominant animals, because subordinates are often prevented from having offspring of their own.

In other animal groups, dominance hierarchies are more complicated. Wolf packs, for example, are led by two dominants who have three subclasses of subordinates below them. Other animals have only one dominant leader with all other animals below him or her being exactly equal. Once an animal has established dominance, challenges to the order are rarely made from within the group, since animals are reluctant to fight other animals that are bigger, stronger, or more aggressive than they are themselves. Sometimes, however, animals from outside the group can successfully challenge and overthrow a long-time leader, but this is rare.

In more intelligent species, such as baboons, factors beyond mere size and strength determine the dominance hierarchy. Age seniority, hormonal condition, maternal lineage, and personality are sometimes factors that affect dominance in more intelligent animals. In baboon groups, furthermore, hierarchies are often elaborate. Adult males are dominant over less mature males and females; yet a fully mature female can be dominant over a less mature male. A dominant baboon displays its superiority with rapid “fencing” manoeuvres, open-jaw displays, and hitting.

Close Bonds Among Animals

Animals with complex nervous systems, ranging from some fish to mammals, may form monogamous bonds. The mates of such species stay together for a breeding season or even for a lifetime. Their social ties are not restricted by the time-bound, immediate stimulation that simpler animals need. However, monogamous pairs must be able to identify their mates from other con-specifics This requires the intricate action of an advanced nervous system.

Some birds and many mammals band in large groups, such as herds and families. These groups include adult males and females and offspring of different ages. The offspring in most mammalian groups remain with the group until they reach sexual maturity. The females frequently remain until the group splits up. Some socially bonded groups of mammals consist of an older male, a number of younger males, many females, and immature offspring. Among the howler monkeys and some other mammals, the younger males band together into a marginal bachelor group until each establishes himself as the older male in a new social group.

Not all mammals maintain elaborate group arrangements. Many live fairly solitary lives, coming together only for mating. Afterwards, the female remains with the litter until the young become juveniles or are sexually mature. In some instances, the mating pair stay together until the young are born. Beavers behave in this way. In other instances, the male and the female separate immediately after mating. This is true of many other rodents.

PARASITES.   Leave a comment

Bed bug

An organism that lives on or within another organism, called the host, and that gains its sustenance from the host organism is known as a parasite. Parasites occur among all the major groups of living things. There are parasitic fishes for example, the lamprey, which attaches itself to other fishes and sucks their body fluids. There are many parasitic arthropods, including fleas, lice, biting flies, and mosquitoes.

Many worms are parasitic. Some live in their host’s digestive tract and feed on the food that passes through. Some attach to the intestinal wall and suck the host’s blood. Some, such as those that cause trichinosis, enter the host through the digestive tract and then burrow into the tissues of the entire body. Some also parasitism plants.

Many fungi are parasitic. The rusts are fungi that are responsible for many diseases of major food plants. Parasitic bacteria are responsible for diseases ranging in severity from acne and tooth decay to such major plagues as the Black Death.

The viruses are unique in that they are all parasitic. They are the smallest of the parasites and may enter the host through the respiratory system or may be spread through sexual contact.

Characteristics

 As originally defined, parasites included any organisms that live by drawing food from a host organism. Defined in this broad way, parasitism included relationships that ranged from benign to harmful and even fatal to the host. The term parasitosis was later developed to describe those forms of parasitism that injure the host, and today the term symbiosis describes benign or even mutually beneficial associations between organisms.

Effects on the host. A parasite’s effect on its host is determined by various factors. Many parasites, for example, do not reproduce in their hosts, or reproduce only to a limited degree. Such parasites, including many parasitic worms, produce eggs that enter another host before they develop. The damage done by such parasites depends in part on the number of parasites in the host, known as the host’s parasite burden. Many hosts can carry a light parasite burden that is, they can support a small number of parasites and suffer no ill effects. A heavy parasite burden, however, may cause severe injury to the host.

In the case of parasites that may undergo unlimited reproduction in their hosts for example, the protozoans, bacteria, and viruses the factors determining the final effect on the host can be quite complicated. The ability of the hosts’ natural defences to destroy the parasites often plays a major role. Very young, old, or weak hosts that have limited defences may be severely harmed by large parasite populations that are able to develop unchecked.

Varieties. Parasites are commonly described in terms of their relationships to their hosts. Parasites that remain on the outer surfaces of their hosts are called ectoparasites. Parasitic arthropods are usually ectoparasites. Endoparasites are parasites that live within the bodies of their hosts. The various parasitic worms that live within the hosts’ digestive tracts are endoparasites. Many endoparasites actually dwell within the tissues of their hosts, not just in the cavities of the hollow organs. The bacterium Mycobacterium tuberculosis, the most common cause of human tuberculosis, lives within the cells of the lung tissues.

Bedbug, a small, flat, bloodsucking insect (Cimex lectularius), of reddish-brown colour, of order Hemiptera, family Cimicidae; is parasitic on humans.

Parasites may be permanent or temporary residents in or on their hosts. The bedbug is a temporary parasite. It crawls onto its host to feed and then returns to its hiding place, where it spends most of its life. The flatworm that causes a form of human schistosomiasis is a permanent parasite. Once it enters a host’s body, it remains there until it dies.

Some organisms can live either as parasites or as free-living forms; they are called facultative parasites. For example, the free-living protozoan Naegleria fowleri, which occurs in streams and lakes around the world, can cause infection of the brain after it enters the noses of swimmers. Other organisms, called obligate parasites, can live only a parasitic existence. Plasmodium falciparum, an organism responsible for a form of human malaria, is an obligate parasite.

Autoecious parasites are parasites that complete their life cycles within a single host. Many parasites, however, have quite complex life cycles and may require more than one host. In some cases the immature stages of the parasite develop in one host, and maturation and sexual development occur in a second host. Hosts in which the immature stages of the parasite develop are referred to as intermediate hosts. Parasites that require two or more hosts to complete their life cycles are referred to as heteroecious.

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

The pattern of having more than one host can sometimes provide parasites with a means of spreading. The protozoan that causes malaria has two hosts: humans and certain other animals, and anopheles mosquitoes. Asexual reproduction occurs in infected humans and animals, and sexual maturation, fertilization, and reproduction occur in infected mosquitoes. The protozoans depend on the mosquito to transmit them from one human host to another.

Methods of transmission. An organism that transmits a parasite, as the anopheles mosquito does, is called a vector. Vectors need not transmit parasites by biting, however. Some vectors transmit parasites when they are eaten by the hosts. Certain tapeworms that infect cats and dogs use fleas as vectors. When the cat or dog swallows a flea that is caught during grooming, the immature forms of the tapeworm emerge from the flea’s body and mature in the cat’s or dog’s intestine. The mature tapeworm produces numerous eggs that then pass out of the animal’s body with its faeces and contaminate the environment. If an immature, or larval, flea ingests the tapeworm’s eggs as it feeds on the infected faeces, it becomes infected in turn. The parasite’s life cycle is completed if the cat or dog catches and eats the mature infected flea. A situation such as this, in which a parasite (the tapeworm) is parasitic upon another parasite (the flea), is referred to as hyper-parasitism

Human Parasites

Parasitism in humans is widespread, but the type of parasite varies with geographic regions and social conditions. In areas where sanitation is poor, parasites that are spread by ingestion of faecal-contaminated food and water are common. In areas where housing is inadequate, parasitic insects may be common.

In parts of the world with adequate sanitation and housing, parasites transmitted by faecal contamination and biting insects are generally rare, but those transmitted by direct contact and through the respiratory system may still be common. The parasites that cause measles, mumps, and chicken pox, for example, can spread rapidly in crowded school environments.

Plant Parasites

Arthropod, animal of the phylum Arthropoda comprising invertebrates with external skeleton, segmented body, and jointed appendages.

In many respects the parasites of plants are similar to the parasites of animals. The arthropods, fungi, worms, bacteria, and viruses that parasitic plants may either grow on the plant’s surface or invade the plant’s tissues and, in the case of arthropods that suck plant fluids, may also transmit other parasites, particularly viruses.

Some plants have become parasites on other plants. The simplest form of plant parasitism is that in which the parasitic plant uses its host only for support. The strangler fig, a tropical tree that is grown as a common house-plant, slowly surrounds its host tree until the host dies. The fig then has access to the light above the forest canopy and can grow unhindered.

Other parasitic plants, such as the mistletoe, have a somewhat greater dependence on their plant hosts. Mistletoe grows on trees and uses them for support. In addition, though it makes some of its own food, the mistletoe sends modified roots into its host to draw out nutrients.

Dodder, a leafless parasitic plant introduced into U.S. from Europe with clover seeds; now a rapidly growing pest.

The most complete form of plant parasitism is that in which the parasite relies completely on the host for sustenance. Dodder, for example, is a parasitic vine that draws all its nutrients from its host.

Special Types of Parasitism

Entomologists, scientists who study insects, have described a type of parasitism in which one insect, usually a species of wasp, uses another insect to brood its young. This type of parasitism is called parasitoidism. The parasitoid wasp lays its eggs in or on the host insect, commonly a caterpillar. The wasp’s larvae develop inside the host, feeding on its body, and emerge as full-grown adults. Parasitoidism is being used by some farmers as a means of pest control. Various parasitic wasps, for example, are used to help control agricultural pests.

Another unusual form of parasitism is brood parasitism, which is common among certain birds, particularly the cow-bird and the cuckoo. In this form of parasitism, the parasitic bird lays its eggs in the nest of another species. The host bird then raises the intruder’s young as though they were its own.

A type of parasitism called social parasitism occurs among certain communal insects. Some species of ants, for example, kidnap and enslave the workers of other ant species.

Assisted by Julius P. Kreier, Professor of Microbiology, Ohio State University, and author of ‘Parasitic Protozoa’.