text: Social insects commonly use trail pheromones. For example, ants mark their paths with pheromones consisting of volatile hydrocarbons. Certain ants lay down an initial trail of pheromones as they return to the nest with food. This trail attracts other ants and serves as a guide. As long as the food source remains available, visiting ants will continuously renew the pheromone trail. The pheromone requires continuous renewal because it evaporates quickly. When the food supply begins to dwindle, the trail-making ceases. Pharaoh ants (Monomorium pharaonis) mark trails that no longer lead to food with a repellent pheromone, which causes avoidance behaviour in ants.
  Repellent trail markers may help ants to undertake more efficient collective exploration. 
  The army ant Eciton burchellii provides an example of using pheromones to mark and maintain foraging paths. When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the colony to the new nesting site.
  Gregarious caterpillars, such as the forest tent caterpillar, lay down pheromone trails that are used to achieve group movement.