The Spider's Silk and Web
On the tips of its spinnerets are many fine tubes through which the spider draws out a fluid produced in glands in the abdomen. The fluid hardens into individual strands. By bringing the tips of the spinnerets together, the spider unites the strands into a single thread.
Spider's silk is extremely strong and has a great deal of elasticity. It is extremely thin and lightweight; a thread long enough to reach around the world would weigh less than six ounces (170 g). The term cobweb is often used to describe one or more individual threads. It is also used as another term for a spider's web.
Spider silk is similar to, but not identical with, the silk produced by the silkworm and similar caterpillars. Spider silk, however, is of little value commercially. It does not stand up well to the weaving process, and attempts to weave fabric from spider silk have resulted in fabrics lacking luster and other desirable qualities. It was once used extensively for cross hairs in telescopic sights and other optical instruments, but has been largely replaced for this purpose by platinum wire and glass etching.
Besides using silk to build webs, nests, and cocoons, spiders also use silk for traveling. To lower itself a spider fastens a thread to a twig or other object and then swings off, paying out thread as it falls. This type of thread is called a dragline. The spider often uses the dragline to escape danger, quickly climbing on it to get back to its point of attachment. Many spiders spend their entire lives attached to a dragline.
Many spiders, especially young ones and very small ones, use their silk for a method of travel called ballooning. In ballooning, a spider releases silk threads from its spinnerets. As the wind blows, air currents take hold of the silk and carry the spider along. By this method spiders can be carried for great distances—some have been found more than 50 miles (80 km) out to sea.
There are many kinds of web-building spiders and many kinds of webs. Some spiders build funnel-shaped webs, some build webs that are flat or curved sheets. Some webs are messy jumbles of threads, while others, called orb webs, have a beautiful spokelike pattern.
Spiders spin many kinds of webs. But all webs are used for the same thing—to capture prey.
The threads in a spider web are thin and hard to see. If an insect comes along, it may not see the web until it is too late. Its legs and body get stuck on the sticky strands of silk. The more the insect struggles, the more trapped it becomes.
Some spiders sit and wait in the middle of their webs. The spider may not see a trapped insect. But the spider can feel it tug and pull on the web. The spider knows that dinner has arrived.
Other spiders sit on the edge of their webs. When they feel tugs, they use draglines to swing down onto their prey.
Many people think that orb weavers spin the prettiest webs. These webs are especially beautiful when they are wet with morning dew or covered with frost.
Orb webs are large and round. The main threads look like the spokes on a bicycle wheel. These threads are made up of dry silk. Threads of loose, sticky silk connect the spokes. The sticky threads are the ones that trap the spider’s prey.
Why doesn’t a spider get caught in its own web? There are two reasons. First, a spider knows where the sticky threads are in its own web. It can avoid these threads. Second, spiders have special claws on their feet. The claws keep a spider from losing its grip and falling onto the sticky strands.
Orb weavers are fussy builders. A spider may tear down its web each night and build a new one. It may even eat the old web to recycle the silk.
Some spiders spin tangled webs with threads that go every which way. Others spin sheet webs that hang like hammocks between leaves and branches. Still others spin funnel webs.
A funnel web is shaped like a funnel—wide at one end and narrow at the other. The funnel-web spider hides in the narrow end. It waits for an insect to fly or to crawl into the wide end of the web. As the prey struggles to free itself, the spider runs out and kills it.
Funnel-web spiders are sometimes called grass spiders. This is because they usually build their webs in the grass or along the ground.
Spiders spin webs to capture prey. They wrap their prey in silk. They spin nests to live in. But most female spiders also spin silk sacs to hold their eggs.
The number of eggs a female lays depends on her size. An average-sized female lays about 100 eggs at a time. A large spider may lay as many as 2,000 eggs at one time.
After laying her eggs, a female spider wraps them in a silk cocoon called an egg sac. Then she puts the egg sac in a safe place. Some spiders hang their egg sacs in their webs. Others attach them to leaves or plants. Still others carry their egg sacs with them.
Spiderlings, or baby spiders, hatch inside the egg sac. But they don’t come out right away. They need to be able to spin their own silk before they can leave the safety of the sac.