Why is this the answer?

The answer is spider because this clever riddle describes exactly how this small, amazing creature uses its special silk to move around. Think about a bird or a bee they use wings to fly through the air. A spider is very different. It does not have wings, but it can still travel far and wide and even drop down from high places. That is the first clue: "I move without wings." The second clue, "Between silken string," points to the spider's incredible home. A spider's web is like a beautiful, sticky net made from a very strong, thin material called silk. This silk is the spider's 'string.' It is important to know that spiders make this silk right out of their own bodies, which is a very special talent. When the spider is busy catching food or just traveling across its home, it is moving right "between" all the strands of that silk web. They are always surrounded by their own special creation. The last clue is a bit sneaky and says, "I leave as you find, My substance behind." Have you ever been walking outside and noticed a single, thin, almost invisible thread of silk floating in the air, or seen one attached to a tree branch? That tiny thread is the silk that the spider makes. As it moves from a high spot to a low spot, or even just walks along, it always lets out this silk line. It leaves this silky trail the "substance" behind for you to find. The silk line is left just as it was created, even after the spider has moved on to a new adventure. This riddle uses tricky, poetic language to describe the simple, everyday actions of a busy spider. It tells a wonderful secret about one of nature's best little builders that does not need wings to travel.