WHY INSECTS ARE SMALL.

Auckland Star, Volume LX, Issue 146, 22 June 1929, Page 3 (Supplement)

WHY INSECTS ARE SMALL.

Why are insects small? If you come to think of it, even the largest of them do not grow very big. "A stick insect" may be a foot in length, but it is very skinny in proportion to its length. The main reason for this seems to be that insects have no lungs. Vertebrates (creatures with backbones, such as fish and animals) take oxygen into their bodies through the lungs or gills, and then it is carried to all parts of the body by the blood. Insects take oxygen in by means of tiny tubes, called tracheae, which open to the air at many different points on the surface of their bodies. By their breathing movements they can renew the air in the outer parts of the tracheal system, but the oxygen has to penetrate the finer branches by means of diffusion. This is a very slow business. If an insect had any part of its body more than a-quarter of an inch from the air it would always be short of oxygen. If you look at insects you will see that whatever their length may be they are hardly ever more than a-quarter of an inch thick. Crustaceans, such as f rabs and lobsters, are built on somewhat the same general plan as insects, but they carry the oxygen in their blood. And they grow much larger than any insects. Perhaps it is just as well. How would we get on with mosquitoes or March flies as big as a lobster ? We are sometimes surprised by the activity of insects. A grasshopper is a wonderful jumper, and the much smaller flea can leap two feet into the air. It is easy to imagine that if a fiea were as large as a man it could jump to the height of a thousand feet. As a matter of fact, the height to which a creature can jump is by no means in proportion to its size. For one thing the resistance of the air is greater for the larger animal. For another, to jump a given height requires an expenditure of energy which is in proportion to the weight of the jumper. The smaller the jumper the smaller the amount of energy required. Indeed, it has been calculated that the jumping muscles of the flea, though they can contract more quickly than our own, are really less efficient in proportion to jveight. Otherwise a flea ought to be able to jump six feet instead of two.