Foraging ants trade off further for faster: use of natural bridges and trunk trail permanency in carpenter ants


Trail-making ants lay pheromones on the substrate to define paths between foraging areas and the nest. Combined with the chemistry of these pheromone trails and the physics of evaporation, trail-laying and trail-following behaviours provide ant colonies with the quickest routes to food. In relatively uniform environments, such as that provided in many laboratory studies of trail-making ants, the quickest route is also often the shortest route. Here, we show that carpenter ants (Camponotus rufipes), in natural conditions, are able to make use of apparent obstacles in their environment to assist in finding the fastest routes to food. These ants make extensive use of fallen branches, twigs and lianas as bridges to build their trails. These bridges make trails significantly longer than their straight line equivalents across the forest floor, but we estimate that ants spend less than half the time to reach the same point, due to increased carriage speed across the bridges. We also found that these trails, mainly composed of bridges, are maintained for months, so they can be characterized as trunk trails. We suggest that pheromone-based foraging trail networks in field conditions are likely to be structured by a range of potentially complex factors but that even then, speed remains the most important consideration.

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We are grateful to Camila Moreira, Farley Silva, Felipe Prado and Lucas Paolucci for the assistance in the field and José Henrique Schoereder for the help with the statistical analyses. RGL was funded by CNPq, and SLE was a recipient of a CNPq productivity grant. We also thank the anonymous reviewers for their helpful suggestions.

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Correspondence to Raquel G. Loreto.

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Communicated by: Sven Thatje

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Loreto, R.G., Hart, A.G., Pereira, T.M. et al. Foraging ants trade off further for faster: use of natural bridges and trunk trail permanency in carpenter ants. Naturwissenschaften 100, 957–963 (2013).

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  • Foraging trail
  • Trunk trail
  • Carpenter ant
  • Optimal foraging