title: Foraging grass-cutting ants (Atta vollenweideri) maintain stability by balancing their loads with controlled head movements.
abstract: 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.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK. km498@cam.ac.uk
authors.forename: Karin
authors.initials: K
authors.lastname: Moll
authors.forename: Flavio
authors.initials: F
authors.lastname: Roces
authors.forename: Walter
authors.initials: W
authors.lastname: Federle
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001000:Ants / Q000502:physiology*; D001522:Behavior, Animal; D019416:Head Movements / Q000502:physiology*; D008124:Locomotion / Q000502:physiology; D008297:Male; D004856:Postural Balance / Q000502:physiology*; D011601:Psychophysics; D014892:Weight Perception / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*
references.citation: Arthropod Struct Dev. 2004 Jul;33(3):273-86
references.pmid: 18089039
references.citation: J Exp Biol. 1994 Jul;192(1):119-27
references.pmid: 9317463
references.citation: J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2009 Nov;195(11):1011-20
references.pmid: 19756648
references.citation: Anim Behav. 2000 Dec;60(6):781-788
references.pmid: 11124876
references.citation: Physiol Rev. 2000 Jan;80(1):83-133
references.pmid: 10617766
references.citation: Oecologia. 2002 Apr;131(2):319-324
references.pmid: 28547700
references.citation: J Exp Biol. 1994 Dec;197:251-69
references.pmid: 7852905