For insects, flexibility in the performance of terrestrial locomotion is a vital part of facing the challenges of their often unpredictable environment. Arthropods such as scorpions and crustaceans can switch readily from forward to backward locomotion, but in insects this behaviour seems to be less common and, therefore, is only poorly understood. Here we present an example of spontaneous and persistent backward walking in Cataglyphis desert ants that allows us to investigate rearward locomotion within a natural context. When ants find a food item that is too large to be lifted up and to be carried in a normal forward-faced orientation, they will drag the load walking backwards to their home nest. A detailed examination of this behaviour reveals a surprising flexibility of the locomotor output. Compared with forward walks with regular tripod coordination, no main coordination pattern can be assigned to rearward walks. However, we often observed leg-pair-specific stepping patterns. The front legs frequently step with small stride lengths, while the middle and the hind legs are characterized by less numerous but larger strides. But still, these specializations show no rigidly fixed leg coupling, nor are they strictly embedded within a temporal context; therefore, they do not result in a repetitive coordination pattern. The individual legs act as separate units, most likely to better maintain stability during backward dragging.
The authors declare no competing or financial interests.
The experiments were planned by S.E.P. and M.W., and carried out by S.E.P., V.L.W. and M.W. The data were analyzed by S.E.P. and V.L.W. The paper was written by S.E.P. and M.W.
The University of Ulm provided basic financial support and infrastructure.
Data are available from the authors on request. Videos are available from the Dryad Digital Repository at http://dx.doi.org/10.5061/dryad.7k82t.
Supplementary information available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.137778/-/DC1
- Received January 21, 2016.
- Accepted April 29, 2016.
- © 2016. Published by The Company of Biologists Ltd