Category Physics

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.

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.