Subterranean termites search for food and moisture and will squeeze through cracks as narrow as 1/32 of an inch to get to it! They can make their way through expansion joints, foundation cracks, very small gaps around plumbing, and service entries. Once they penetrate into your home, if unnoticed, the damage can be quite significant.
Drywood termites can survive without any contact with soil. Entry points into your home include your attic and any floor in your home.