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Navigation plays an essential role for many animals leading a mobile mode of life, and for central place foragers in particular. One important prerequisite for navigation is the ability to estimate distances covered during locomotion. It has been shown that Cataglyphis desert ants, well-established model organisms in insect navigation, use two odometer mechanisms, namely, stride and optic flow integration. Although both mechanisms are well established, their mode of interaction to build one odometer output remains enigmatic. We tackle this problem by selectively covering the ventral eye parts in Cataglyphis fortis foragers, the eye regions responsible for optic flow input in odometry. Exclusion of optic flow cues was implemented during different sections of outbound and inbound travel. This demonstrated that the two odometers have separate distance memories that interact in determining homing distance. Possible interpretations posit that the two odometer memories (i) take on different relative weights according to context or (ii) compete in a winner-take-all mode. Explanatory values and implications of such interpretations are discussed. We are able to provide a rough quantitative assessment of odometer cue interaction. An understanding of the interaction of different odometer mechanisms appears valuable not only for animal navigation research but may inform discussions on sensor fusion in both behavioural contexts and potential technical applications.

Desert ants, Cataglyphis fortis, use path integration as a major means of navigation. Path integration in three dimensions requires measurement of three parameters, namely, direction, distance and slope of travelled terrain. Directional information is provided by a celestial compass, while distance measurement is accomplished by a stride integrator, or pedometer. By manipulating leg lengths in foraging desert ants we were also able to change their stride lengths. Ants with elongated legs or shortened legs, take larger or shorter strides, respectively, and misgauge travel distance. Travel distance is overestimated by experimental animals walking on extended legs, and underestimated by animals walking on shortened legs strongly indicative of stride integrator function in distance measurement. High-speed video analysis was used to examine the actual changes in stride length, stride frequency, and walking speed caused by the manipulations of leg length. The predicted changes in homing distance are in quantitative agreement with the experimental data, further supporting the pedometer hypothesis. We also examined a possible role of the hair receptors (established to function in graviception) situated between head, alitrunk, petiole and gaster in for slope detection in 3D-path integration of the desert ant. Cataglyphis judges the ground distance when travelling over hills, allowing correct homing even in uneven terrain. We eliminated the function of these hair sensors either by shaving the hairs, or by immobilizing the joints monitored by the hair plates. With that major component of their sense of graviception eliminated, one would expect the ants to disregard, or at least misgauge, the ascents and descents performed across hills during outbound journey. Surprisingly, neither shaving nor immobilization of the hair sensillae affected correct path integration, across both, uneven terrain and level surface.