Diane Amati, age 10, of Philadelphia, Pa., for her question:

IS IT TRUE THAT SPIDERS ARE NOT INSECTS?

This is true, quite true. The leggy little spiders tend to remind us of the leggy little insects, but they are classed in separate groups. The differences between our sizable cows and horses are plain to see. Actually there are greater differences between the spiders and insects. We just do not notice them so much because these creatures are quite tiny.

Scientists, as we know, have sorted all the animals into groups. To do this tricky work, they do not judge much by size, otherwise they might class the spiders and insects together. Instead, they go by certain body features, such as legs and wings. For example, in order to qualify as an insect, a little creature must have six legs  no more and no less. Every spider has eight legs  and right away this disqualifies her from being an insect. And this is not all. An insect may or may not have wings, either one pair or two pairs. No spider has wings of any sort. Every qualified insect has a body in three parts, with a thin neck division and a skinny waist between his chest and tummy section. A spider has a two part body. You cannot see any neck division because her head and chest are joined to form one section. However, she definitely has a skinny waist between her tummy section and her united head and chest section.

Actually these are very outstanding differences. After all, cats    and dogs, cows and horses all have a bulky body with four legs and a tail  and no wings. Yet we can tell at a glance that they do not belong in the same animal groups.

When classifying the animals, scientists also look for differences in their way of life. For example, insects dine mostly on plant food, though some eat a little meat. Spiders eat only meat  and their favorite food is insect meat. Both spiders and insects lay eggs. But many insects go through a hungry caterpillar stage before they hatch into the adult stage. All baby spiderlings are minicopies of their mamas  and they molt their skins as they grow.

True, the spiders and insects are alike in certain ways. They are small critters. They all have boneless bodies held together inside a tough skin of some sort. But their differences are so outstanding that it would be unfair to class them all together in the same group.