If they colide with an object they will go in a go around mode and will choose at random a direction between left and right. This choice is influenced by the pheromones arround. Then they will rotate themself in this direction until they can progress. They keep the same direction as long as the object is at sight to prevent them from always changing direction all the time and follow none in practice.
The going arround object start to look nice but we have performance issues the pheromones that we are trying to solve. When it will be working properly with the pheromones the best side of the object should emmerge from the pheromones left before, since the shortest path should have more pheromones, but for now they just pick a direction at random.