Trail disruptions of army and leaf-cutter ants

Study by Brady Hartman, Sophia Kruger, Alyssa Risch, and Mary Thelen.

Both army ants and leaf-cutter ants are prevalent species at La Selva Biological Station in the Caribbean lowland wet forest of Costa Rica. While they differ in their traveling methods and type of nests, they both use pheromone trails to ensure everyone follows the same path. The goal of this study was to determine whether species of ant, width of the ant trail, or flux of ants moving on the trail was correlated with a faster response time when an obstruction was placed in their path. We found trails of army or leaf-cutter ants and measured the flux in ants per second. We took photos of the trails and calculated the width of the trail using the program ImageJ. We then placed an obstacle in their path and measured the time between placing the obstacle and the re-formation of a fluid path. Our results showed that army ants were significantly faster at responding to the obstacle than leaf-cutter ants. There was no significant relationship between width of the trail and response time. Nonetheless, wider ant trails could lead to stronger pheromone trails, so future research should consider this. There was also a significant interactive effect of species and ant flux on response time. While higher flux of leaf-cutter ants was correlated with quicker response times, potentially due to a stronger pheromone trail, this relationship was much weaker with army ants. Based on our results and army ants’ ability to maintain a consistent response with varying flux, we believe that army ants are more systematic in their travel methods than leaf-cutter ants.