This is a simulation of artificial ants foraging from a nest, discovering a food source in the face of obstacles, and then establishing a trail between the nest and food source. The model uses two pheromones which set up gradients to the nest and to the food source respectively. The pheromones evaporate and diffuse as well.
A two-pheromone model is likely not biological; but it has led to a series of nice papers dynamic-programming-ish artificial trail creation, which you can find at http://cs.gmu.edu/~eclab/