I see termites a lot. When I am splitting wood for my wood heater I find them in the wood. It is a natural part of the process of the decomposition process of wood that has been in contact with the ground. The termites consume the wood and return it to the soil. In nature it is a good thing. When they get into the wood in your home it is bad. They can destroy a board in just a few days. If left alone, they will move from the first board to the next and beyond. They are very sneaky in their approach. Termites need water and they need food. If they have both then there is nothing to stop them from destroying a home. We use pressure treated lumber in areas that are exposed to the elements and/or the ground. The treatment in the lumber makes it undesirable as food to the termites. We also use masonry products such as block or brick in areas that contact the ground. This is a good deterrent to the destructive bugs.
A good pest control company can treat the ground around your home in order to set up a perimeter barrier to keep them out. Regular inspections around the foundation of the house is a good practice also. Look for the signs of termite activity. They have to get to the ground in order to get water. Below you will see a picture of a dirt tunnel that they build in order to get back and forth without being exposed. Non-treated wood in contact with the ground can be a route also. Call in a professional if you suspect that they might be in the woodwork.