Mark Raymond, age 11, of St. Catherine, Ontario, Canada, for his question:

How many spider species are there?

Some people would shudder to hear that we share our world with more than 30,000 spider species. These folk abhor all spiders and regard them as creepy crawly little horrors. True, some spiders inflict deadly wounds    when molested. But it's hardly fair to give them all a bad name. After all, they devour insect pests, which qualifies them as our allies.

A few people still think of spiders as fat furry insects, with long legs and no wings. True, they are classified in the huge Phylum Arthropoda, which also includes the insects and crustaceans. But the spiders are different enough to merit a class and order of their own. We call them arachnids because they belong in the Class Arachnida and the Order Araneae. These names were borrowed from a legendary maiden of ancient Greece, who was famous for her spinning.

All spiders are born spinners, though some species spin only one silken thread. Others weave elaborate linings for their nests and many species spin strong, gauzy webs to trap insects. Every spider has a two part body, separated by a waist. Eight spidery legs are attached to the front section, which includes the head and thorax. The hind section is a bulging abdomen, with spinnerets built into the tail end.

The Araneae Order is subdivided into many families, numerous genera and more than 29,000 known species. This does not include the unknown species, which may increase the list of spider species to 50,000. Some spiders are no bigger than pinheads. Giant tarantula spiders are as big as a man's hand. Most of the ones we see are females because usually the males are eaten early in life. Let's face it, lady spiders and baby spiderlings are cannibals.

Each species, of course, has her own life style. Most of her activities are centered around trapping her insect food and producing offspring. The average spider lays 100 or so small soft round eggs. A large tarantula may lay 2,000 or more. In most cases, special silk is used to enfold the eggs in a cozy, protective cocoon. The wolf spider fixes her egg sac to her tail and totes it around until the mini spiderlings hatch from their little pearly eggs.

Water spiders live in streams and ponds. They weave bell shaped webs to trap and hold bubbles of air below the surface. Fisher spiders slide on top of the water in pursuit of water insects and even tadpoles. Some of the stocky crab spiders can change color to match the flowers among which they live. All spiders can spin at least three and usually as many as five different threads, thick or thin, dry or sticky.

All spiders have jaw pincers with poisonous glands to stun their victims. Only six species have venom that is dangerous to humans. One of these is the deadly brown recluse spider. Another is the long legged black widow spider, who wears a scarlet triangular sign on the underside of her abdomen.