Nutan Shukla T HERE are many animals who use sense of touch to find food. Under the sea, starfish and sea-urchins creep about on the sea floor and use touch, together with a sense of smell, to find and to examine a prospective meal. At the bottom of the deep sea, bright red prawns with exceptionally long feelers and deep sea fish with long, under-chin barbels, many times the length of the body, are thought to use these structures, not only to find their way about like a blind man with a stick, but also to make contact with food. All these creatures are in close contact with the surface film and are able to locate prey, trapped in the surface tension, by the tell-tale ripples that emanate from their struggling bodies.
Sense of sight has no meaning for the animals living in dark caves.
It is inappropriate to the extent that many of these creatures have lost their eyes altogether, and can range from blind crickets and cave-fish to blind salamanders. Some of the cave-dwelling creatures depend on smell, whereas many of them have adaptations of parts of the body to afford a better sense of touch. Waiting for the prey, garden spider sits at the side of its circular web with its one leg on a tension line. If the vibrations are too great, the spider will ignore the signal because they could be either created by large animal or wind. They could also be due to a large insect which will work itself free and fall out The spider knows if the insect caught in the web is small its struggling legs will create the just right kind of vibrations and the spider will dash out and immobilise the prey with a single, poisonous bite.