Pheromones are chemical factors that trigger a social response in members of certain organisms, like the Hymenoptera, the order to which ants belong along with bees and wasps. Pheromones can help ants retrieve food, sound an alarm, find a mate and affect other behaviors as well. This question really depends on what species of ant you are referring to. In the big-headed ant, when a scout locates a dead insect, the pheromone it lays back to the nest results in multiple individuals coming to retrieve the dead prey. The trail is strongest when freshly laid but has a rapid rate of decay - after 6 minutes, it has no effect. This reduces competition with other ant colonies living in the area. Some trails of pheromones may cover a long distance and last a long while. For example, in the Texas leaf cutting ant, they need to travel as far as 100 m or more to a source of leaves for their fungus gardens. Their pheromone trails may persist for months at a time. In contrast, fire ant trails are very short lived and may only cover a distance of 1 m or less to a trail of food and then fade out rapidly once the food has been used up.