Janet Wilks, age 13, of Arab, Ala., for her question:

Why do people claim that a spider is not an insect?

There was a time when ordinary folk classed the spider along with the bugs and the beetles. Nobody argued about it. But we live in the age of science and more folk tend to listen to the experts. And according to the experts, the spider is not classed with the insects.

There are so many different creatures in the world that even an expert biologist could not count them one by one. What's more, the wearisome job would not teach him very much. He is, however, helped by finding relationships and similarities. He sees important relationships between animals and plants and their surroundings. He wants to know how living things get along together and adjust to the problems of their world.

Naturally, he needs to identify the different creatures. He uses an international system of classification and fellow experts of different languages can understand each other. All the world's insects axe grouped together in the scientific class called insecta. The class is subdivided into about 25 separate orders. The different insects outnumber by far all the other different animals in the world. But the spider is not among them.

In order to belong in the class insecta, an animal must have certain very definite physical features. His body must be built in three well defined sections, a head and a thorax and an abdomen. He must have six legs, three on each side of his thorax. He is allowed one pair of antennae, one or two sets of jaws plus simple or compound eyes, or both. He also may have two pairs of wings.

The spider is the same size as many insects and at a glance she seems to be somewhat bug shaped. But a closer inspection shows that she cannot qualify as a member of insecta. If you count them, you will find that she has eight spidery legs. She also has two instead of three sections to her body. Her head and thorax are fused together to form the front section and her abdomen forms the tail section. The abdomen of an insect is circled with stiff segments. The spider's abdomen is soft and unsegmented. And she never has wings. These features disqualify her from insecta and along with 30,000 other spiders experts classify her in the class arachnida.

There are spiders with one or two, three or four pairs of eyes and some have no eyes at all. There are spiders with four, six or eight spinnerets for spinning silken thread. All spiders catch and eat fresh meat and most of them have poisonous fangs. Each species has its own way of coping with the problems of its little world, its own special story for those who are interested.