Well, first of all the pests themselves usually are completely hidden from view during their normal activities, and come to light only when an inspection of the hidden areas is performed, or damage is broken into and discovered during remodeling. Since the majority of termite species live in colonies in the ground it now is a mystery to you how to stop them. Termites are insects. The colony was started years ago by a Queen and King termite, that crawled or flew to that spot from some other colony, where they originated. Now, before we start to hate termites too badly, please understand their role in nature, and the importance of that role.
Nature recycles everything eventually.
Plants and animals eventually die - perhaps in several thousand years if it is a Knobcone Pine from the southwest desert mountains, or in just a few days if it is a little Mayfly. Even rocks are recycled, by water, lichens, animals, and other influences that attack the rock's structure, and this may take millions of years, eventually creating gravel or soil that is more useful for the growth of plants. When a tree dies it no longer serves to provide its intended function - shade, oxygen production, new trees from seeds. At the moment it dies recycling processes begin, and one of those is the rapid degradation by insects, termites included. Termites eat the wood, creating large pockets in the previously solid mass, allowing other animals and moisture in, and eventually the once solid tree is reduced to sawdust and humus that can be reused by the forest.