Eastern damp-loving termites are essential to forest ecosystems as decomposers, yet not welcome munching on your house. They move in if any wood in your house is in contact with the soil and/or you have moisture problems anywhere else. Crawlspaces are especially vulnerable because they are close to dirt and are warm in the winter, if not properly ventilated or contain a furnace. (Termites normally have to chill out during the winter and not eat.) Porches that are built over earth are other usual entry points for the tiny pests.
Main evidence of infestation include the presence of mud tubes (that the insects use to avoid drying out away from the soil—none are usually more than two feet long), regular channels eaten along the grain of the wood (lined with saliva adhering mud), and swarming. Ants also swarm, but termites have two sets of equally sized wings and thick bodies.
New treatments, that are less invasive than flooding all the soil around the foundation with termiticide, include baits that can be placed in the ground away from the house. Encouragingly, 60,000 termites only eat the equivalent of a one foot 2x4 in six months, so you can take your time to find the right treatment plan.