Sally Neal, age 10, of Birmingham, Ala., for her question:
HOW DO SPIDERS SPIN WEBS?
Spiders as a group have seven kinds of silk glands for making webs, but no specific type of spider has all seven kinds. All spiders, however, have at least three kinds of silk glands and most kinds have five.
Each kind of gland produces a different type of silk that the spider uses for a particular purpose.
Some silk glands produce a liquid silk that becomes dry outside the body. Other glands produce a sticky silk that stays sticky.
The "spinnerets," small projections which actually spin the silk, 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 silk from different silk glands and produce a very thin thread or a thick, wide band.
The spider can also make a sticky thread that looks like a beaded necklace. A spider uses beaded threads in its web to trap many kinds of jumping or flying insects.
Spiders depend on silk. Wherever a spider goes, it can spin a silk thread behind itself. This thread is called a "dragline." The dragline is sometimes called the spider's lifeline because the animal often uses it to escape from enemies.
If danger threatens a spider in its web, it can drop from the web on its dragline and hide in the grass. Or, if it so decides, the spider can simply hang in the air until the danger has passed. Then it can climb back up the dragline into its web.
The common house spider spins a loosely woven tangled web of dry silk, held in place by long threads attached to walls or other supports. The center of the web forms an insect trap.
The platform spider spins a silk sheet below a net of criss crossed threads. Flying insects hit the web net and,fall into the sheet.
The tangled spider spins a triangular web between two twigs. The web uses both dry and sticky silk.
Orb weavers build the most beautiful and complicated of all webs. They weave their round webs in open areas, often between tree branches or flower stems. Threads of dry silk extend from an orb web's center like the spokes of a wheel. Coiling lines of sticky silk connect the spokes and serve as an insect trap.
Some webs, such as the one produced by the orange garden spider, form a large orb web that may measure more than 2 feet across. The spider spins a zigzagging band of silk across the middle of the web.
Did you know that there are more than 29,000 known kinds of spiders? Scientists say, however, that there may be as many as 50,000.
Many persons think that spiders are insects. Scientists tell us they are arachnids, which differ from insects in many ways. Spiders have eight legs. Ants, bees, beetles and other insects have only six legs.
Most insects have wings and antennae or feelers. Spiders have neither.