Foraging grass-cutting ants (Atta vollenweideri) maintain stability by balancing their loads with controlled head movements
- 326 Downloads
Grass-cutting ants (Atta vollenweideri) carry leaf fragments several times heavier and longer than the workers themselves over considerable distances back to their nest. Workers transport fragments in an upright, slightly backwards-tilted position. To investigate how they maintain stability and control the carried fragment’s position, we measured head and fragment positions from video recordings. Load-transporting ants often fell over, demonstrating the biomechanical difficulty of this behavior. Long fragments were carried at a significantly steeper angle than short fragments of the same mass. Workers did not hold fragments differently between the mandibles, but performed controlled up and down head movements at the neck joint. By attaching additional mass at the fragment’s tip to load-carrying ants, we demonstrated that they are able to adjust the fragment angle. When we forced ants to transport loads across inclines, workers walking uphill carried fragments at a significantly steeper angle, and downhill at a shallower angle than ants walking horizontally. However, we observed similar head movements in unladen workers, indicating a generalized reaction to slopes that may have other functions in addition to maintaining stability. Our results underline the importance of proximate, biomechanical factors for the understanding of the foraging process in leaf-cutting ants.
KeywordsTerrestrial locomotion Load Static stability Adaptation Atta
This study was funded by a Dissertation Grant from the UK Biotechnology and Biological Sciences Research Council, by the German Academic Exchange Service (DAAD), by the Cambridge European Trust, by the Balfour Fund of the Department of Zoology (University of Cambridge), and by the German Research Foundation (DFG, Sonderforschungsbereich SFB 554/TPE1). We thank Martin Bollazzi for helpful discussions and Thomas Endlein for technical support. We are much indebted to Alejandro G. Di Giacomo and the Götz family for allowing the collection of the ant colony at the Reserva Ecológica El Bagual (Alparamis SA - Aves Argentinas) in Eastern Chaco, Province of Formosa, Argentina.
- Abdel-Aziz YI, Karara HM (1971) Direct linear transformation from comparator coordinates into object-space coordinates in close-range photogrammetry. Proceedings of ASP symposium on close range photogrammetry. Urbana Illinois, USA, pp 1–18Google Scholar
- Fowler HG, Forti LC, Pereira-da-Silva V, Saes NB (1986) Economics of grass-cutting ants. In: Lofgren CS, Vander Meer RK (eds) Fire ants and leaf cutting ants—biology and management. Westerview Press, Boulder, pp 18–35Google Scholar
- Hölldobler B, Wilson EO (1990) The ants. Harvard University Press, CambridgeGoogle Scholar
- Jonkman JCM (1976) Biology and ecology of the leaf-cutting ant Atta vollenweideri. Z Angew Entomol 81:140–148Google Scholar
- Jonkman JCM (1980) Average vegetative requirement, colony size and estimated impact of Atta vollenweideri on cattle raising in Paraguay. Z Angew Entomol 89:135–143Google Scholar
- Lighton JRB, Bartholomew GA, Feener DH Jr (1987) Energetics of locomotion and load carriage and a model of the energy cost of foraging in the leaf-cutting ant Atta columbica Guer. Physiol Zool 60:524–537Google Scholar
- Lutz FE (1929) Observations on leaf-cutting ants. Am Mus Novit 388:1–21Google Scholar
- Roces F, Bollazzi M (2009) Information transfer and the organization of foraging in grass- and leaf-cutting ants. In: Jarau S, Hrncir M (eds) Food exploitation by social insects: ecological, behavioral, and theoretical approaches. Contemporary topics in entomology series. CRC Press, Boca Raton, pp 261–275Google Scholar
- Schmitz J (1993) Load-compensating reactions in the proximal leg joints of stick insects during standing and walking. J Exp Biol 183:15–33Google Scholar