Terminates cause billions of $'s in property damage a year in the US according to the National Pest Management Foundation. You usually don't notice them until the damage is already extensive. That is why it is important that prior to purchasing a house you have a pest inspection done by a licensed inspector.
Home owners can take some preventative measures such as keeping moisture away from their home's foundation, store mulch, firewood and wood chips away from the house, ventilate crawl spaces, eliminate gaps and cracks along roof eaves and window joints. Still the best defense is to schedule regular inspections with a termite specialist who can use special wood treatments and repellants to help prevent termites. The bottom line is don't let termites destroy your biggest investment...your home!