A spider's silk-making organ. has hundreds of small openings. Silk comes out of these openings as a liquid, and, as it reaches the air, it becomes thread-like. These tiny threads combine to form a single, solid thread. The spider can make many different kinds of thread. The threads can be thick or thin, wet or dry sticky or wooly Each kind has a different purpose Some webs create an egg case others provide hiding places. The most common purpose of a spider web, however, is to catch food.