Pheromone trails

In going with the insect theme something I would like to implement is a way to communicate via "pheromone" trails.  This will be something that will fade over time and can only be seen by members of ones faction or via special equipment that scouts will have. This way people can leave a trail back to useful materials when they have found them, and it will provide a "ball of string" for those exploring caves.  This will probably be accomplished by a simple line painting on the ground, or glowing footsteps.  It will also be something that you can turn on or off.  I'll have to look into what it will take to set it up.