Sunday, October 12, 2003		Nature

BELONGING to an ancient group of insects, cockroaches, one of nature's most efficient waste disposers, have not changed much since they appeared more than 30 crore (300 million) years ago on the floor of primeval humid and warm forests of the distant past when most of our deposits of coal were being laid. Armed with a tough, shiny shell and mouth parts well adapted for chewing these arthropods (jointed-limbed animals) can run at speed of 3km per hour.

The success of the insect's survival for such a long time and that too without any change in its body design shows that its flattened body is best suited to its habitat and the kind of life it leads. Living in the company of human beings where there is plenty of food and artificial warmth, cockroaches can smell food with their long, pointed antennae and eat almost anything that could possibly be eaten—from human food items to even papers and book bindings. Their flattened body is very helpful for crawling under floorboards, or between narrow cracks and crevices.

These arthropods are medium to large in size and most of the 3500 species known are nocturnal, keeping away from light. Species include burrowing, cave-dwelling and amphibian cockroaches too. All the members of the family have long antennae and long, spiky legs and are very hardy creatures. They have been known to live for weeks even after their heads are cut off. Usually considered as domestic pests, they are fast running insects and their ability to react with lightning speed makes them almost impossible to catch. These prolific breeders are capable of adapting easily to desert conditions and tropical rain forests without any difficulty.

They first appeared eons ago as giant-sized creatures scurrying on the forest floor, living under fallen leaves and dead vegetation in humid tropical forests. But why did they shrink to the present-day size later? Nothing is known for sure. Not much time has passed since they took humans to be their new companions and have not only invaded their dwellings but have travelled, accompanied and colonised many continents with them.

Among the many species, the so-called American cockroach Periplanea Americana, which is also said to be the true citizen of the world and is found in almost every human habitation, is a prolific breeder and its female lays more than 1000 eggs in her lifetime of about four years.

Though cockroaches are found amid filth, they keep their body absolutely dirt-free and spend all the leisure hours in grooming it. Extremely shy of light and exposure, this group of beetle-like insects, related to the mantises, do not have sharp eyesight, but are highly sensitive to changes in light conditions and sound waves that are detected by means of sensory hairs on a pair of protruding organs at the tail. Besides, they are equally alert to ground vibrations and are able to make out a movement which could be less than one-millionth of a millimeter.

Cockroaches never attack humans, but they taint everything that comes into contactwith them with their obnoxious smell and are also carriers of disease-causing agents.