After 30 years in the business, I can tell you that you have drywood termites in Houston, BUT, they do not drop and spread as you show in the picture. The droppings normally form a well defined cone.   I don't think they are termites based on one picture. 
Take the droppings to a local Agricultural extension agent. They will be to ID them, using local knowledge, and then provide a recommendation for control.  Professional knowledge and advice for free.  A rare example of your taxes working well.
Good luck and keep us posted.