A lot of people ask me, "How did I get these termites in my home?" Well, there is an answer, but it is a long one. Without explaining the habits of Subterranean Termites, it is difficult for a homeowner to understand how and why they are inside the house.
If I could give a one-word answer though, one that would define the nature of a termite colony that allowed it to get where it got, is the word "Foraging". "What is that?", You ask. Foraging is the natural habit of Subterranean Termites that drives them into anything that has wood fibers. It could be your tree stump in the back yard, a wood pile up against the house, or simply wood siding that is too close to the soil. All these conditions will encourage a termite colony already present in the ground to be tempted to check out your house. By "check out", I mean look for any accessible wood. I do not mean exposed wood necessarily. Even though your foundation sill is not exposed to the outside, it is accessible to a termite who needs only 1/32 of an inch to get in!
Termite foraging is the process that termites use to find their food. It may not just be wood that they are looking for, but moisture. Subterranean Termites need lots of moisture, so wet conditions around your home will contribute to foraging near your foundation. Damp crawl spaces could also be a problem that can encourage foraging termites to check out your house. If you do not have a concrete floor in a crawl space, you might have termites tunnel under the crawl space foundation and come right in. I have seen termites built "shelter tubes" (dirt tubes that they use to keep moisture when traveling out the ground itself) right out of the dirt in a crawl space and go straight up into a joist. What is amazing, is that the moisture guided them in; the joist was the pot of gold.
Do not ever let a foraging colony of termites fool you, just because they are outside, does not mean they can not get in. Given enough time, along with natural settling that a home has, can allow for termites to wait until the opportune time, and bam-there in! When it comes to Subterranean Termites, foraging can be a problem for your home unless you are aware that they are already there.