My Science School

A thin coating of oil on the surface of the spider's legs prevents them from sticking to their own web.

Spiders have 3 pairs of spinnerets (silk spinning apparatus) located beneath the hind tip of their abdomen. Silk, made up of proteins, secreted by the silk glands, and are made into fibres as thin as a thousandth of a millimetre. The threads we see are actually a bundle of these fibres. The proteins are water soluble when secreted, but when made into a fibre, some Physical and chemical changes take place, and so, after a while the fibre becomes tough and does not dissolve in water. In fact, it becomes stronger than a steel wire of the same thickness. Hence, the spider silk is also used to make bullet proof vests.

To construct a web, the spider first lays the radical threads. These resemble the spokes on a wheel and they radiate from the centre or hub of the web. The radial fibres are then connected by spiraling threads. There may be 10-60 turns in a web. To capture the insects, spiders scatter small glue droplets throughout. The glue droplets remain sticky by absorbing moisture from the air. They also increase the capacity of the web to resist wind forces.

While some spiders do not place glue droplets around the central area of their web so that they can wait there for the prey, a few others attach a separate 'signal thread' from the web’s centre to a nearby place (not on the web) where it can conveniently relax. When the insects get stuck to web, spiders sense the vibrations and leap on the prey.

To help avoid being caught in their own webs, the spiders secrete oil and coat it on their toes. One can test this by dipping a spider’s legs in ether, an organic solvent, which dissolves the oil. If the spider is returned to the web after the dip, it will be caught in its own web.

Snakes are stone deaf, yet they respond to charmers’ mahudi. Though this appears a contradiction the fact is that snakes actually respond to vibrations produced on the ground and not to the sound waves produced by the mahudi, in the air. Snakes do not have ears; instead they have a long bony rod called columella auris that extends from fenestra oval is to the quadrate bone. It is this bone which helps the snake to detect the vibrations.

One would have noticed that charmers first hit the ground with the pipe before playing it. The snake picks up the vibrations on the ground thus caused and comes out. When the snake charmer sways his pipe as he plays, up, down and forward, the snake too sways its body in the direction of the mahudi, only considering it as an object to be targeted and not because it follows the music. In some experiments, snakes have responded even without the ground tap because in these cases the tin in which the snake is housed is made to vibrate by the music (air waves) generating from the pipe. 

Stings of insect group animals like mosquito cause skin lesions by direct effects of the insect parts or secretions which cause irritation. When the insect parts or secretions are retained for some time they tend to cause hypersensitivity responses. The immediate itching effect on the site of the bite is the appearance of urticaria or inflamed papules. Histologically the lesion shows a wedge shaped per-vascular infiltrate of the lymphocytes, histocytes and eosinophils within the dermis. The first event of the inflammation is an increased blood flow to the bite area. This results mainly due to the arteriolar dilation. Another event is the increased vascular permeability which results in the accumulation of protein rich extra vascular fluid.

The major chemical mediator of inflammation is the histamine. It is widely distributed in the tissue, the richest source being the mast cells that are normally present in the corrective tissues adjacent to the blood vessels. Preformed histamine is present in mast cell granules and is released by mast cell de-granulation process which in response to the stimulus caused due to irritation at the site of the bite. This histamine causes dilation of the arterioles and increase vascular permeability of venules. This in turn causes venular endothelial contraction and widening of the interendothelial cell Junctions, where the extra-vascular fluid accumulates causing, inflammation.

 There are more than 1,200 species of mosquitoes but all of them do not feed on the blood of mammals. The three important blood feeders found throughout the world are Culex, Anopheles and Aides. Even in these species, only the female mosquitoes suck blood, while the males thrive on plant sap and honey from flowers. The blood when drawn enters the highly dilatable stomach of the female which uses it for reproductive purposes. At least one-fifth of a drop of blood is sucked at a time. If these female mosquitoes are killed, they bleed.  Unfed females and males do not bleed when killed.

Some sleep out of the water, and some may not sleep at all. The furred or hairy aquatic mammals in the Pinniped order (like seals) have a variety of interesting adaptations that permit them to spend a comparatively long time under water sometimes at considerable depths, according to the Encyclopedia of Mammals.

            However they rise frequently to breathe and emerge from the ocean to sleep, relax, molt, mate and reproduce on a sandy beach or rock above the water.

            The situation is less clear for cetaceans (whales) and sirenians (sea cows and manatees). The whales evolved from land animals that returned to the sea, millions of years ago.

Though whales come to the surface to breathe air into their lungs, they can spend a long time between breaths, up to an hour in   some species, and spend nearly all their lives under water. However, whales learned to hold their breath so well that they lost their involuntary breathing mechanism and must be conscious to continue to breathe. Not only would a reflex have to take care of breathing, he said, it would have to take them to the surface for air.

Also, the blow hole automatically closes and must be opened voluntarily by the whale. Whales would drown if they fell asleep or were knocked unconscious. Sea cows and manatees tend to live in warm, calm, shallow, vegetation-rich waters where they can float lethargically at or near the surface.   They have an extremely low metabolic rate, do not expend much energy to regulate body temperature and require little oxygen.

Manatees may sleep or rest supported by the bottom. When they hold their breath, large blubber deposits and natural buoyancy let them float at the surface and engage in a resting behaviour, though not an unconscious sleep. 

    Firefly also known as lightning bug is the common name for about 100 species of insects found throughout the tropical and temperate regions. Fireflies are soft-bodied insects measuring` from a few centimetres to about a few tens of centimetres. They have generally dark brown sheath-like front wings covering the flying wings at rest, yellow or orange markings and luminescent glands located on the underside of the rear abdominal segment. Both sexes emit intermittent light signals often seen in meadows on late-spring and summer nights, to attract mates. The luminescent larvae and females of some species are also called glowworm. The firefly emits light by allowing oxygen, breathed through its abdominal tracheae, to combine with a substance called luciferins. The fly also controls the timing and duration of the flashes, for example, to attract its mates. The unique characteristic of the fly is that it emits light without producing heat.

            The process of emission of ‘cold’ light by living beings by various enzymatic reactions is termed bioluminescence or chemiluminescence. The glowworms, Lampyris noctiluca, are bioluminescent insects. The light produced may either be extracellular (outside the cells) or intracellular (inside the cells). Luciferin, a substance present in glowworms gets oxidized in the presence of an enzyme called luciferases to give light and carbon dioxide. Emitted light may be blue, green, yellow, red, orange or a combination of these colours.

            The intensity of the colour also differs among various animals. It is said that when 10 Phyrophorus noctilucus are kept in a glass bulb, one can read printed pages comfortably.

            The animals use this cold light to procure food, to escape from predators, as warning signal and as mating signal. During photosynthesis radiant energy (light) is converted into chemical energy (starch) by plants. But during bioluminescence the chemical energy in the body is converted into radiant energy, without raising the temperature in the process.

            In glowworms, a combination of adenosine tri phosphate (ATP) and oxidative energy is used in a set of reactions that convert chemical energy into light energy. Generation of light flash requires activation of luciferins by an enzymatic reaction with ATP in which a pyrophosphate cleavage of ATP occurs to form luciferyl adenylate. This compound is then acted upon by molecular oxygen luciferases to bring about the oxidative decarboxylation of luciferins to yield oxyluciferin. The intermediate step of this reaction is accompanied by emission of light. Luciferin is then regenerated from oxyluciferin subsequently.

 The object of blinking of our eyelids is to keep the front of the eyeball clean. Blinking is done by means of muscles in the eye lids and the cleansing by tears. The tears are secreted in a little gland and carried along to the eye and when our eyelids open and close the tears are poured over the front of the eye and they wash away any particles of dust or any other harmful substances.

            Some animals like the snake for example, do not have eye lids and hence cannot blink. But there is a hard film or scale over the eyes to protect them from dust and injury.

         

 

 

 

 

 

  The energy is gathered from nectar, and the butterflies that make the trip, those born in the early fall, are able to convert nectar into fat.

            “Those born in September know to tank up on nectar,” said Dr. David Marriott, founder of the Monarch Program, a nonprofit research and education organization based in Encinitas, Calif. “Their abdomens get really large.”

            Unlike the other generations, these monarchs, he explained, have a little area of fatty tissue where the sugar of the nectar is converted into fat. They can live off this cushion in winter and need only water to rehydrate their bodies.

            Monarchs born in September or late August live seven or eight months, sometimes nine, Dr. Marriott said. Their children, grandchildren and great-grandchildren live just a month.

            “By the time you get to the great-great-grandchildren it puts us back to September again,” Dr. Marriott continued. The butterflies also feed while migrating, he said.

 

The snakes are the only vertebrates which have efficiently overcome the handicap of absence of limbs making them survive with relatively long, slender body and a cosmopolitan habitat bestowed on them by nature. This achievement was basically by adapting different modes of locomotion fulfilling the need of the environment (terrestrial, water and arboreal) in which the animals lives.

The most common mode of progression which is generally employed by all species and is characteristic to them is the ‘serpentine type of locomotion’ better named as ‘undulatory motion’ in which the animal forms a zigzag track.

The basic necessity and attribute of this motion is some form of maximum provided by any projections or depressions on the substratum like rocks, branches, twigs, dust, sand or pebbles. This roughness in real sense resists the long, slender body to move on a straight line owing to which the body assumes a position of a series of s-shaped horizontal loops or curves.

 Each loop or curve which faces some resistance in turn delivers an equal and opposite thrust against the resistance leading to the formation of a series of  lateral or horizontal waves produced by a flow of muscular  contraction and relaxation passing from head to tail, resulting in the , propulsion of the  body in the forward direction.

 This kind of a zigzag motion is undergone only when the surface is rough enough to offer maximum resistance. It is of no use when they move on a really smooth surface, where they are offered least resistance. 

 

            Fireflies are not really flies and glow worms are not really worms. Fireflies are soft bodied beetles in the family of Lampyridae and glow worms are actually young fireflies (larvae).

            Although the luminescent molecule in many organisms is yet undetermined, in most organisms the light producing reaction is mediate by the action of a class of enzymes called luciferases on their substrate called luciferins.

            Some organisms do not make use of luciferases but instead use calcium activated photo proteins in their bioluminescent reaction involves the oxidative decarboxylation of luciferins in the site of special cells called photocytes present on their lower abdomen segments to attract mates. It appears that male fireflies flashing patterns are mating signals and females seem to prefer the most rapidly flashing males.

            Since glow worms do not mate, no one knows exactly why they glow. But glow worms are carnivorous and probably use the light to lure or locate its prey.

            There are over 2000 species of fireflies inhabiting the tropical and temperate regions. Fireflies of the same species recognize each other by number of flashes used the frequency of flashes and colour of the light. Fireflies’ eggs are also reported to glow.

     Ants are social insects. Many ant species go out of their nests in groups in search of food. Initially, a few worker ants, called scouts, go out of the nest in search of food. Once an abundant source of food is found to the nest, it presses its abdomen to the ground and at frequent intervals extrudes its sting, the tip of which is drawn lightly over the ground surface, much like a pen drawing a thin line.

            As the sting touches the surface, a volatile chemical (trail pheromone), flows out of a gland (Dufour’s gland), associated with the sting. In this way the worker draws an invisible chemical line from the source of food to the nest. As soon as it returns to the nest, it contacts a couple of workers, antennates them and makes quick looping movements on the line for short distances. This excited movement attracts the attention of more workers and they start following the scout, which leads, initially, to the food. These workers return to the nest with more samples, and reinforce the chemical line while returning.

            This results in recruitment of more and more workers and soon one will find a never ending line of ants moving up and down the line bringing back food. Since the chemical is highly volatile, the trait remains only for a short time. Hence, all the worker ants constantly draw the line over and over again.

 

            Ants manage to float on water due to an interesting property, known as surface tension, of liquids. In any liquid, the constituent molecules are in constant motion. They slide over one another, maintaining some freedom of motion while exhibiting enough attractive force to hold the molecules close to each other. This enables the liquid to flow.

            But the attractive forces in a column of liquid are not the same at all points. Molecules at the centre of the liquid are subjected to uniform forces all around. But a molecule at the surface is subjected to unbalanced forces. Strong attractive forces exerted by the molecules amongst themselves pull the liquid inwards. That means, the molecules at the surface feel an excessive force pulling inwards. The net result is that the liquid behaves as though it has an invisible elastic ‘skin’ which always tries to contract and decrease the surface area. This contractive force on the surface of the liquid is called surface tension.

            Now let us come to the actual question: Ants are so light that their weight is not sufficient to overcome the surface tension and break the contracting forces. If the weight of an ant is, then it will break the elastic membrane and sink. Similar observations can be made by placing a greased needle on a blotting paper which in turn is placed on water. The blotting paper will absorb the water and sink. But the needle floats.

            The fall of a body is controlled mainly by gravitational attraction of the Earth. The gravitational force depends on the mass of the falling object-a heavier object is attracted more than a lighter object. This attractive force is opposed by an upward thrust (resistance) offered by air on the body. This resistance also depends on the surface area of the object. That is, if the surface area is more, the resistance is also more. Thus in any falling object, these two forces compete with each other.

            In the case of an ant, the force of gravity is almost balanced by air resistance and so it is able to land safely. If there is a wind blowing, ants also float away. However, if a cluster of ants or a big ant is forcibly hurled to the ground, they will get hurt. Anyway, it will be difficult to know whether the ant gets hurt or not.

            Antennae, the two hair-like structures on the head of the ants, help them in locating sweets. These chemoreceptor’s help them to perceive smell and taste through minute sensilla, or sensory cells.

             These sensilla can detect accurately the smell in the air. It points towards the origin of the smell by detecting accurately the changes in the concentration of the odoriferous particles. If the sweets are wrapped in paper bags or any other wrappers having minute holes, the odour carried by the air will be sensed by the sensilla. If the antennae are removed, ants cannot identify the smell and distinguish them from other foods.

           

 

 

 

 

 

 Birds have nifty tendon arrangement in their legs. The flexor tendon from the muscle in the thigh reaches down the leg, round the ankle and then under the toes. This arrangement means that, at rest, the bird’s body weight causes the bird to bend its knee and pull the tendon tight, so closing the claws. Apparently this mechanism is so effective that dead birds have been found grasping their perches long after they have died.

            Yes, birds do sleep. Not only that, some do it standing on one leg. And even more surprising, may be hypnotized into sleep at will. To try it, we will have to bring our eyes close to the cage, and use the hypnotist’s principles on our eyes. If we act as if we are gradually falling asleep the bird will follow us, finally holding one leg up under its belly, tucking its head under its wing and falling into a deep sleep.

            What’s more most pet bird owners know that all we need to do make the pet fall asleep is to cover the cage with a blanket to simulate night.

            Birds do sleep, usually in a series of short ‘power naps’. Swift are famous for sleeping on the wing. Since most birds rely on vision, bedtime is usually at night, apart from nocturnal species, of course. The sleeping habits of waders, however, are ruled by the tides rather than the Sun. some other species are easily fooled by artificial light. Brightly lit city areas can give songbirds insomnia.