To Cathy Whitty, age 11, of Ottawa 3, Ont., Canada, for her question:

How do insects breathe?

Insects are small animals, too small for us to SEE their features in detail. When we use a magnifying glass, the close up view of an insect is often very startling. He may look like a miniature monster from Mars, but he must breathe his oxygen from the atmosphere of the planet Earth.

Compared with cats, dogs, horses and other mammals, the inaects are very odd animals indeed. They,too, Must Eat, grow, breathe and hand on life, but they have their own odd ways of doing these things. They  odd because they are different

From the life processes of the animals we know well.

Insects have blood, but not red blood. If you swat a mosquito, she may ooze reddish liquid, but this is the red blood she has just sipped from her victim. As a rule, insect blood is whitish yellow, sickly green or colorless. It is liquid, and it is circulated through a system of tubes by a heart of sorts. An insect's heart is an inner tube as long as its body. Its duty is to pump blood through the system.

An insect needs a constant supply of fresh oxygen, just as you do. You have lungs and a nose with nostrils to take air into and out of your lungs. Your oxygen is dissolved in your blood and sent circulating through your system by your pulsing heart. An insect has no lungs and no heart. It has nostrils, but not where you would expect them to be. It has a breathing system that takes in oxygen and also returns waste carbon dioxide to the air.

An insect's nostrils or breathing pores are called spiracles, and he may have six or Eight pairs of them. They are along his sides. HE is a segmented animal, and as a rule he has six or Eight pairs of spiracles on the Segments of his abdomen and perhaps two pairs of spiracles on his thorax.

Fresh air seeps in through the spiracles and filters down through a network of tubes called the tracheae. The inner tissues grab the oxygen they need and pour our. Their carbon dioxide. In time, the waste gas finds its way to the spiracles and seeps out into the air. The pinhole spiracles are open doors. Through them, the fresh air seeps inside the insect and the stale air seeps outside.\

An insect has some but not much control over his intake of air. Very dry air could steal too much moisture from his inner tissues and cause him to shrivel. In most cases, he can prevent this dehydration. He can close some of his breathing pores or leave them all open to the air. When the air is very hot and dry, he Sensibly shuts up six pairs or more of his spiracles.