The leaf cutter ant, Atta columbica, must collect a continuous supply of leaves to maintain their fungus gardens, the primary source of food. To move leaves efficiently, the ants clear trails leading from the nest to good foraging sites. These trails can be blocked by branches, stems and other litter falling from trees. When foragers returning to the nest with a leaf piece encounter a large obstacle, they typically drop their burden. The obstacle disrupts the flow of food and must be removed.
The obstacle will be removed from the trail by workers with large obstacles taking from 20 to 30 minutes to move. The ants appear to keep the largest workers in reserve for trail clearing activity. These workers are a cost to the colony, but critical to the colony when needed.
Human roads are subject to the same types of interruptions. A car crash or snow storm can halt traffic until the road can be cleared. We keep tow trucks and snow plows in reserve that are called upon as needed. Most of the time, this investment is idle. They are a cost to human society when idle, but critical when needed.
Jerome J. Howard. (2001) Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica. Behav Ecol Sociobiol 49:348-356
DOI 10. 1007/s002650000314