Costs of trail construction and maintenance in the leaf-cutting ant Atta columbica

Leaf-cutting ants of the genus Atta use trunk trails during foraging which may persist for months or years. The time and energy costs of trail constru ction and maintenance were estimated for colonies of Atta columbica on Barr o Colorado Island. Panama. to deter mine if these costs are likely to const rain new trail construction and promote persistence of existing trails. Lar ge workers 2.2-2.9 mm in headwidth participated in trail-clearing significa ntly more frequently than typical leaf-carriers, indicating that they may f orm a distinctive task group within the foraging force. Small litter items were carried off trails, while large ones were cut up before removal, great ly increasing the costs of removing large litter items. The average time co st of removing a kilogram of litter was estimated at 3.359 ant-hours, and e nergy costs at 4.6 kJ. Colonies maintained trail systems 267 m in length an d 16.5 m(2) in area, and built an estimated 2.7 km of trail with an area of 134 m(2) during a veer. Based on litter standing crop and estimates of lit ter fall rates, total costs to colonies averaged 11,000 ant-days of work an d the energy equivalent of 8,000 leaf burdens. These costs are small relati ve to the number of available workers and rates of mass harvest, suggesting that costs do not significantly constrain trail construction. Instead, tra ils ma! persist because thee provide access to high-quality resources or be cause only a few trails are required to fully exploit the foraging territor y.