Looking for termites when thinking about buying a house
Other than learning how to look for exterior telltale signs of termite damage, such as spent casings and holes in the wood or in the ground, you need to write in a contingency on your offer to purchase for a complete home inspection and/or an additional pest inspection. 

As mentioned above in the comments, hire your own home inspector and/or pest control specialist. DO NOT succumb to the pressure of Realtors to use their favorite inspectors. Find inspectors that truly work for the person that hires them, you! If you are not trained in building construction, inspection, or pest control, do not attempt to evaluate the condition of a home on your own. 

Some Home Inspectors, such as myself, offer screening inspections. This is a simple walk through (apx 1 hour) and initial evaluation of a house before one even makes an offer. This type of inspection is not as comprehensive as a full inspection that can take 2 to 4 hours in home and documents all the aspects of the house, rather it is an hour spent looking for obvious major flaws or situations that will help you determine if you actually want to consider placing an offer. Once you have found a house you are serious about, this screening inspection is usually much cheaper than a full inspection, but since the inspector should be acting as your advocate, can advise you if there are any major issues that would influence your decision to make an offer or not.  For the hundred bucks or so, it can be a huge time saver, allow you to make a more realistic offer, and give you a better feeling of confidence about the home you are making an offer on.   Good Luck.