David Holdren, age 10, of Trout Run, Pa., for his question:

How many kinds of spiders exist? 

Scientists classify spiders according to their way of life. Web spinning spiders spin webs to trap insects. Hunting spiders run after insects or lie in wait for them. There are more than 29,000 known kinds of spiders but scientists believe there may be as many as 50,000 types. Spiders live anywhere on earth where they can find food to eat.

Cobweb is another word for a spider's web. The word comes from the Middle English word coppe, which is short for the Old English word atorcoppe, meaning spider's web.

Cobweb also means thin and gauze like.

Gossamer is another word that fits in here. Gossamer is a thin, filmy substance. Gossamer is made of fine, soft cobwebs that can sometimes be seen floating in the air on calm autumn days.

Small spiders weave gossamer webs on trees or bushes. Slight drafts tear them from their fastenings and they float in the air.

Don't think of spiders as insects. Spiders are classified as arachnids, which differ from insects in many ways. Spiders have eight legs. Ants, bees, beetles and other insects have six legs. Most insects have wings and antennae but spiders do not.

Other arachnids, along with spiders, include daddy longlegs, scorpions, mites and ticks.

Web spinning spiders have fingerlike organs called spinnerets which are used to spin silk. Most kinds of spiders have six spinnerets but some have four or two.

The spinnerets are attached to the rear of the abdomen. The tip of a spinneret is called the spinning field. The surface of each spinning field is covered by as many as a hundred spinning tubes. The tubes send out liquid silk which flows from silk glands in the spider's abdomen to the outside of its body. The silk then hardens into a thread.

Spiders as a group have seven kinds of silk glands. No species of spider has all seven kinds of silk glands but all have at least three with most species having five.

Each kind of silk gland produces a different type of silk that the spider uses for a particular purpose.

Spinnerets work somewhat like the fingers of a hand. A spider can stretch out each spinneret, pull it back in, and even squeeze them all together.

Using different spinnerets, a spider can combine the silk from different silk glands and produce a very thin thread or a thick, wide band.

Some glands produce threads that dry quickly while others produce sticky silk that stays sticky.