I've worked on a lot of old houses in my carpentry career.  The oldest was built in the 1830s.  Very old for Texas.  Supposedly it was owned by the mother of Texas, Jane Long, although they're not 100% sure of that.

They used a lot of long leaf pine and cypress for their houses back then and that's what we found in the houses we were restoring.

Long leaf pine has a tight grain to it.  That means that the annual rings are close together.  It's a very pretty wood.  After 50 years or so it becomes so hard that you can't pound a nail into it.  You have to pre-drill the hole. 

Cypress is a beautiful wood to work with.  Even in age it doesn't become real hard.  Two of its properties are resistance to rot and bugs.  Recently I met a man whose daughter has a house in New Orleans.  When the house was checked after Hurricane Katrina it was pronounced repairable.  The reason is that the house was built of cypress. 

I've also worked on a lot of houses built in the last 40 years.  The major difference is that the wood is southern yellow pine or a species similar to it.  This is a fast growing tree with annual rings that are wide apart, as least compared to long leaf pine.  It's also soft, perfect for termite food and it can rot easily when it gets wet and doesn't dry out.

Most of the time I've seen termites go into a board and stay between the harder, darker ring in the wood.  The first piece of wood they go into gets a lot more eaten up.  Then once they have tunneled into the next board, there doesn't seem to be any desire to eat everything before going on to the next.  They get into the softer part of the grain, then go to the end of the board and into the next one.  Most of the damage I've ever seen has usually only required one or two boards to be replaced.

Now I have heard that Formosan termites are very different than this, but I don't have any experience with them.

I am working from Silverton, Colorado this summer.  Once the mines shut down in the early 1990's, 80% of the town moved out.  The result is that there are a number of houses with repairs needed on the siding and trim. 

As I looked at the areas needing repairs, I realized that there is a major difference between here and the Texas coast.  Humidity.  When it rains up here and the wood gets wet, it dries out within a few hours.  In the humid parts of Texas it could take days.  Lots of time for rot to start its course.

The times have changed.  The economies of house building dictate what goes into the house.  Few of us could afford long leaf pine or cypress.  The best thing is to repair areas as soon as you know there is a problem.  If you can't take care of it right away at least cover it from the rain.  Then on sunny days, uncover it so you know it has dried out.  Then recover it before it rains.