Do you know if they are drywood, dampwood, or subterranean termites?
My experience is with drywood termites, in Florida. A drywood termite colony begins with a single male and female who enter a crevice in a piece of wood, seal themselves inside, and mate. A couple weeks later there will be about 20 young ones, and the adults mate again. They chew on the wood, thereby hollowing out a tunnel in the wood. They obtain all the nutrients they need from the wood, digesting it, and releasing tiny fecal pellets ("frass"), that look like sand, and which they push out of the tunnels through tiny holes. This frass is the only indication humans have that there are termites within the structure. They continue doing this for 3-5 years, at which time the colony has grown to about 2000 termites. At that time, some termites begin to develop wings, and those are the ones that will fly out in the spring, looking for a mate and a new piece of wood to create a new colony. This swarming of termites can continue for a few weeks or months in the spring, usually at night, peaking around sunset and sunrise. Hundreds of the flying termites exit the colony, but the original colony remains in place. That is, 500 may fly out, but there are still 1500 inside the tunnels. The following spring, a new group will develop wings and fly out.
So, if you have drywood termites, the answer to your questions are:
Yes, when you see flying termites, they are coming from a colony has been in existence for several years already.
No, the presence of flying termites this year does not necessarily mean that the previous year's treatment was ineffective, just that it was incomplete. There are at least two explanations:
1. Last year's treatment may have destroyed part of the colony's termites, which are living in tunnels several feet long, with many branches. When poison is injected into a tunnel, it will kill many termites, but termites in a distant part of the tunnel can block off that region, and live happily on for many years in regions of the tunnel that are free of the poison. It can be difficult to completely eradicate the colony in one treatment, so I would not blame the guy if the colony is still active. Did he make only one visit last year, or did he return a few weeks later to check if the colony was still active? (by seeing new frass deposited outside the tunnels, for example)
2. Last year's treatment may have effectively destroyed the colony that you identified at that time, but clearly your house is termite heaven. If one pair found a cozy retreat in a window molding five years ago, and a second pair set up housekeeping in the basement window, and a third pair somewhere else. So the guy may have effectively destroyed several colonies, but not been aware of all of them.
Again, this is for drywood termites. Dampwood and subterranean termites have somewhat different life cycles and living conditions, and I have no experience with them. But I think my answers would generalize to them as well, that is, (a) flying termites reflect a long-term colony, and (b) the local guy should not necessarily be blamed for the reappearance of flying termites this year. They can be hard to get rid of, especially after a single treatment.
