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J Comp Physiol A (2015) 201:645–656
DOI 10.1007/s00359-015-0999-2
ORIGINAL PAPER
Walking and running in the desert ant Cataglyphis fortis
Verena Wahl · Sarah E. Pfeffer · Matthias Wittlinger 
Received: 25 November 2014 / Revised: 4 March 2015 / Accepted: 5 March 2015 / Published online: 1 April 2015 
© The Author(s) 2015. This article is published with open access at Springerlink.com
Keywords Desert ant · Cataglyphis · Stepping pattern · 
Inter-leg coordination · Gait
Introduction
If you are in a North African salt pan in the middle of 
the day, you would probably encounter Cataglyphis for-
tis desert ants pacing around with tremendous speeds on 
their long legs, insects Rüdiger Wehner likes to call “race  
horses in the insect world” (Wehner 2009). Like race horses 
with their shiny and delicate bodies, they can doubtlessly 
exert a fascination on the observer when they attain high 
walking speeds while swiftly manoeuvring through their 
harsh environment, always on the look-out for dead insects 
that succumbed to the heat of the day (Wehner 1983). Indi-
viduals with a prey item, one can see running along an 
imaginary straight line which connects the place where 
they had encountered the food with the nest entrance. The 
kind of navigation that Cataglyphis fortis ants perform on 
their foraging excursions is an approximate form of dead 
reckoning, the so-called path integration where the ants 
are constantly connected to the nest location via an invis-
ible link (Collett and Collett 2000; Wehner and Srinivasan 
2003; Wehner and Wehner 1986, 1990). Combining path 
integration as a navigation mode and high walking speeds, 
Cataglyphis ants maximize their chances of finding food 
and returning to the nest even in the hottest times of the day 
without succumbing to the hostile conditions. To perform 
path integration Cataglyphis ants would need two inputs: 
(1) information about angles steered, that is, the direction 
and (2) information about the distance travelled. Direc-
tional information is provided by a celestial compass (Weh-
ner 1982; Müller and Wehner 1988), and distance informa-
tion is gained by means of a stride integrator (Ronacher and 
Abstract Path integration, although inherently error-
prone, is a common navigation strategy in animals, par-
ticularly where environmental orientation cues are rare. 
The desert ant Cataglyphis fortis is a prominent example, 
covering large distances on foraging excursions. The stride 
integrator is probably the major source of path integration 
errors. A detailed analysis of walking behaviour in Catagly-
phis is thus of importance for assessing possible sources 
of errors and potential compensation strategies. Zollikofer 
(J Exp Biol 192:95–106, 1994a) demonstrated consist-
ent use of the tripod gait in Cataglyphis, and suggested an 
unexpectedly constant stride length as a possible means 
of reducing navigation errors. Here, we extend these stud-
ies by more detailed analyses of walking behaviour across 
a large range of walking speeds. Stride length increases 
linearly and stride amplitude of the middle legs increases 
slightly linearly with walking speed. An initial decrease of 
swing phase duration is observed at lower velocities with 
increasing walking speed. Then it stays constant across the 
behaviourally relevant range of walking speeds. Walking 
speed is increased by shortening of the stance phase and of 
the stance phase overlap. At speeds larger than 370 mms−1, 
the stride frequency levels off, the duty factor falls below 
0.5, and Cataglyphis transitions to running with aerial 
phases.
V. Wahl and S. E. Pfeffer equally contributed to the manuscript.
Electronic supplementary material The online version of this 
article (doi:10.1007/s00359-015-0999-2) contains supplementary 
material, which is available to authorized users.
V. Wahl · S. E. Pfeffer · M. Wittlinger (*) 
Institute of Neurobiology, University of Ulm, 89069 Ulm, 
Germany
e-mail: Matthias.wittlinger@uni-ulm.de
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Wehner 1995; Wittlinger et al. 2006, 2007) which might be 
a major source of navigational errors. To better understand 
the stride integrator, we need a detailed analysis of walk-
ing behaviour and thus the inter-leg coordination across the 
entire range of walking speeds employed by Cataglyphis 
fortis. Zollikofer (1994a) demonstrated consistent use of 
the tripod gait in desert ants and suggested an unexpect-
edly constant stride length as a possible means of reduc-
ing navigation errors. During his time in Rüdiger Wehner’s 
lab, Christoph Zollikofer pioneered the work on walk-
ing kinematics in these fast running desert ants, and since 
then many details have been revealed about the locomotor 
behaviour of Cataglyphis fortis compared to other species, 
namely the influence of speed and curvature, of body mor-
phology and load (Zollikofer 1988, 1994a, 1994b, 1994c) 
or locomotion on sloped surfaces (Seidl and Wehner 
2008; Weihmann and Blickhan 2009). Nevertheless, with 
advanced high-speed videography at hand, we are now able 
to get a more thorough insight into Cataglyphis’ walking 
behaviour. Moreover, we can extend these studies not only 
by more detailed analyses of inter-leg coordination but also 
expand the range of walking speeds to where we assume its 
limits. The aim of this paper is to investigate the effect of 
walking speed on the inter-leg coordination or gait, stride 
length, walking speed and stride amplitude, duty factor, as 
well as swing and stance phase and phase relationships of 
all six legs.
Materials and methods
Ant colonies
High-speed video recordings were performed in the field 
near Maharès, Tunisia and in the laboratory at University 
of Ulm, Germany. For the laboratory recordings, several 
colonies of Cataglyphis fortis were kept and raised under 
annual temperature and daily light–dark cycles based on 
conditions in their natural habitat (20–35 °C, winter–sum-
mer; 14 h:10 h, light:dark cycle in summer). The colonies 
in the laboratory consisted of several hundred ants, with an 
active forager force of approximately 10 % of the popula-
tion size. Estimated from the number of active foragers, the 
field colonies and the colony size were comparable. The 
laboratory ants received water ad libitum and were fed with 
honey water and insects, five times a week.
Experimental procedure
Medium to large sized (2.5–3.3 mm alitrunk length) Cat-
aglyphis fortis ants were individually marked and were 
filmed with a camera placed above the channel while 
they walked in a linear channel with a width of 7 cm and 
channel wall height of 7 cm. We video filmed the run-
ning ants between 0900 and 1600 h. The highest walk-
ing speeds were usually recorded around noon, when the 
highest air temperatures were reached in the field. Channel 
floors were evenly coated with a very fine layer of firmly 
attached white sand (0.1–0.4 mm particle size) to provide 
good traction and thus to facilitate slip-free natural walking 
and running kinematics. Film recordings were made with 
a high-speed camera (MotionBlitz Eosens Mini1, Mikro-
tron Unterschleissheim, Germany) at 500 and 1000·frames 
per second (Fig. 1) and shutter times of 100–200 µs. The 
indoor laboratory video shoots were illuminated with two 
fibre optic cold light sources (Schott KL 1500LCD, 150W, 
Schott AG, Mainz, Germany) whereas videos filmed under 
open sky outdoor conditions needed no external light 
sources since the sun provided plenty light. To get videos 
of very slowly walking desert ants, the channel setup was 
cooled down to about 10–15 °C by means of cooling pads.
Data analysis
In the experiments, the ants walked through the channel 
at different speeds. Both inbound and outbound walking 
ants were considered for the walking analysis. Especially 
in the outdoor video sessions, the inbound walking ants 
sometimes carried a minute food item. Each individual was 
video recorded up to five times, consequently in the data 
of N = 388 runs up to five runs might origin from one ant. 
Only those individuals exhibiting regular straight and lin-
ear walks without de- or acceleration or abrupt stops were 
used for the tests. Each analysed walk contained at least 
three step cycles per leg. A 5 cm long black and white scale 
bar was filmed after each set of videos with the same set-
tings to calibrate the analysed videos. Tarsal footfall posi-
tions as well as times of lift-off (or movement away from 
the contact point) and touch-town of the tarsal tips were 
digitized with ImageJ (US National Institutes of Health, 
Bethesda, Maryland, USA, http://imagej.nih.gov/ij/) on a 
frame-by-frame basis. The duration of swing phases were 
calculated as the difference between the time the tarsal tip 
lifts off the ground and subsequent touchdown of the tar-
sal tip of the same leg for the swing phase or vice versa 
for the stance phase. In the hind legs, the tarsal tip often is 
dragged over the floor without being lifted off the ground. 
Here, we define the moment when the tarsal tip leaves the 
contact point on the floor as start of the swing phase (Rein-
hardt and Blickhan 2014). The onset of stance was used as 
the reference time for the analysis of temporal coordina-
tion of all legs for the phase analyses. The CircStat Toolbox 
in MATLAB was used for phase analyses and the corre-
sponding plots (Berens 2009; Wosnitza et al. 2013). Stride 
frequency is defined as the walking speed divided by the 
stride length. The stride length was calculated for each leg 
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pair (L1, R1; L2, R2; L3, R3) as the mean of each leg pairs’ 
strides in one video sequence. Stride length is specified as 
the measure from two successive footfalls of the same leg 
of one body side (Alexander 2003). A stride should not be 
confused with a step, which is the distance the body cov-
ers from the footfall of a leg pairs’ left leg to the footfall 
of the right leg or vice versa. A stride thus basically incor-
porates two steps, the left and the right. Stride length is 
therefore actually double the step length (assuming the left 
step is more or less the same as the right step and walk-
ing speed is constant). When we look at the tripod shaped 
gait in Fig. 1, one stride describes the relationship of two 
successive triangles of the same colour whereas one step 
describes the relationship of two differently coloured suc-
cessive triangles. In this account, we only employ the term 
stride as mentioned above and as it is defined in Alexan-
der (Alexander 2003). The stride amplitude is a measure 
for the swing of one leg during a stride without the addi-
tional body movement during the swing phase (Wosnitza 
et al. 2013). We calculated the stride amplitude as the stride 
length minus swing phase duration multiplied by walking 
speed. The stride amplitude (Wosnitza et al. 2013) which 
is misleadingly called “stride length” in Hughes (1951) is 
technically a body coordinate based measure for the swing 
movement of a leg. We, however, calculated the mean 
stride amplitude of a run as an indirect measure from geo-
coordinate based data, such as the means of stride length, 
swing phase duration and walking speed. We also assume a 
constant mean walking speed for all runs evaluated. There-
fore, minor errors might occur. Although a certain variabil-
ity of walking speed within a step cycle might be observed 
especially for the slow walks, we only evaluated video 
sequences with a constant mean walking speed over several 
step cycles. Mean walking speed was measured from the 
start of the first step cycle to the end of the last step cycle in 
one video sequence.
We calculated the tripod coordination strength (TCS) 
which evaluates the quality of the tripod coordination (Wos-
nitza et al. 2013; compare also Spagna et al. 2011). First, 
we calculated the time from the earliest swing onset to the 
latest swing termination. This gave us time t1, during which 
at least one of the three legs was in swing phase. Then we 
determined time t2, during which all three legs were in 
swing phase at the same time. The ratio t2/t1 then described 
the TCS. A TCS of 1 indicated perfect tripod coordina-
tion; it approached 0 when the temporal relationship of 
swing phases shifted to other coordination patterns (Wos-
nitza et al. 2013). The duty factor, a ratio of stance phase 
Fig. 1  Tripod gait of a fast running and a slowly walking Catagly-
phis individual. Six complete strides—three of each body side—cap-
tured by high-speed video are shown. Tripods formed by the right 
front and hind leg (R1, R3) and the left middle leg (L2) are drawn in 
red; tripods formed by the left front and hind legs (L1, L3) and right 
middle (R2) leg are drawn in blue. Stride length (s) was determined 
as the distance between two successive footfalls of the same leg. a 
Very fast running ant showing the typical tripod gait (s = 19.8 mm; 
v = 597.4 mm s−1). b A rather slowly walking ant also showing the 
typical tripod gait, however, with reduced stride length (s = 9.1 mm; 
v = 95.2 mm s−1). Single video frames of the ant, taken during the 
first and sixth captured steps, are pasted into the tripod analysis fig-
ure
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to cycle period can be used as a measure that describes the 
transition from walking to running (Alexander 2003). We 
measured the cycle period as the time between successive 
touchdowns of the same limbs. Thus, one gait cycle begins 
when the reference foot contacts the ground and ends with 
subsequent touchdown of the same foot. Since cycle period 
of very slow walks gets more variable and calculations of 
TCS or duty factors do not deliver appropriate, compara-
ble values, we carried out a separate evaluation of walking 
behaviour during slow locomotion (Fig. 5). We did a frame-
by-frame analysis of 76 videos within a speed range of 4.5 
to 29.9 mms−1 (five different speed groups I–V) by clas-
sifying each frame according to its gait pattern similar to 
the work of Mendes et al. (2013). Each frame was assigned 
a certain colour and a number representing the different leg 
coordination types. For the different leg combinations used 
for our gait analysis, see supplementary material. If none of 
the listed leg combinations was found, the frame was clas-
sified as ‘undefined’. For each of our five speed groups, we 
calculated a percentage distribution of different leg combi-
nations, which the ants applied during slow walks. Further, 
the frames’ gait index was averaged for each video and 
pooled according to the five speed groups to accomplish a 
more inter-individual comparison. Statistical analyses were 
performed with SigmaPlot 11.0 (Systat Software Inc., San 
Jose, California, USA). Pair-wise comparisons (Fig. 5) and 
comparisons of slope and y-intercept (Figs. 3a, 6b) were 
performed with a t test, since respective groups were all 
normally distributed. We fitted data with linear, power and 
polynomial functions and calculated R2 in Microsoft Office 
Excel 2013.
Results
The walking parameters of Cataglyphis fortis were evalu-
ated spatially and temporally over the entire walking speed 
range from 4.5 to 619.2 mms−1.
With increasing walking speed, the stride length 
increases in an almost perfectly linear fashion (Fig. 2a). 
The faster the ant runs, the longer the strides get. The stride 
length increases more than fourfold over the entire speed 
range from 3.5 mm (at 4.5 mms−1) to 19.8 mm (at 589.5 
mms−1). Stride frequency increases as a function of walk-
ing speed and levels off at a frequency plateau of around 
30 Hz beginning somewhere between 300 and 400 mms−1 
(Fig. 2b). In the desert ants, the start of the frequency pla-
teau is a first indication that the ants attain aerial phases. 
Ants that are achieving longer strides, increase stride fre-
quency to a maximum at which the frequency reaches the 
upper level while the strides are still getting larger. From 
this point on, walking speed is increased by increasing 
stride length only. To maximise stride length in spite of a 
stagnant stride frequency, the ants become “airborne” from 
footfall to footfall to cover a larger distance (Fig. 2c).
The stride amplitude (Wosnitza et al. 2013), is a body 
coordinate based measure for the swing of a leg. The stride 
amplitude of the middle leg shows a good linear correlation 
with increasing walking speed. The amplitude of the mid-
dle legs doubles, whereas the amplitudes of front and hind 
legs do not increase significantly and show only a weak 
correlation (R2 = 0.28, front legs; R2 = 0.66, middle legs; 
R2 = 0.20, hind legs) (compare Fig. 3a). For the middle leg, 
Fig. 2  General walking parameters, stride length, stride frequency 
and walking speed and their relationships. Only middle leg data are 
plotted; each data point represents one video sequence (N = 388). a 
Stride length as a function of walking speed for the entire walking 
speed range. Linear regression is indicated; y = 0.023 × x + 5.93; 
R2 = 0.93. b Stride frequency as a function of walking speed. Best fit 
regression is indicated; y = −0.0001 x2 + 0.11x + 1.63; R2 = 0.97. c 
Stride frequency as a function of stride length. Best fit regression is 
indicated; y = −0.115x2 + 4.78x − 19.77; R2 = 0.81. The grey hori-
zontal bar highlights the frequency plateau (b, c)
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this means that 66 % of the variability can be described by 
the linear regression model.
Since Cataglyphis is known to employ tripod coordina-
tion over most of the walking speed range (Seidl and Weh-
ner 2008; Wittlinger et al. 2006, 2007; Zollikofer 1988, 
1994a), we evaluated the quality and synchrony of the tri-
pods by means of the tripod coordination strength (TCS) 
(Wosnitza et al. 2013; compare also Spagna et al. 2011). 
The variability of the TCS decreases with increasing walk-
ing speed and at the same time converges towards the max-
imum levels of around 0.7 to 0.85. From a walking speed of 
around 300 mms−1, the variability is least whereas at lower 
speeds, the TCS varies between 0.02 and 0.78. Above walk-
ing speeds of around 300 mms−1, t2 and t1 of the TCS both 
remain at constant levels of 12–22 ms (t2) and 24–34 ms 
(t1). To further analyse the inter-leg coordination and the 
phase relationships of the tripods, we made footfall pat-
terns or podograms that show the swing and stance phases 
of every leg as black (swing) and white (stance) bars along 
a timeline (Fig. 4a–d). The podogram in Fig. 4a shows a 
very slow locomotion. This walk with 6.9 mms−1 is at the 
lower edge of walking speed and exemplifies that calcula-
tions used for the walking speed larger than 30 mms−1 (e.g. 
TCS and duty factor) do not provide any useful informa-
tion in this case. Therefore, slow walks were analysed and 
quantified separately in Fig. 5. In contrast, the podograms 
of the higher walking speeds (Fig. 4b–d) beautifully show 
tripod coordination. The green bar in Fig. 4b highlights the 
stance phase overlap where all six legs are on the ground 
at the same time (hexa support phase) for a relatively slow 
walk. The blue bar in a very fast run (Fig. 4d), however, 
exemplifies the swing phase overlap (aerial phase) which 
is the time where the ant is airborne—all legs lost ground 
contact—except for some cases where the hind legs 
might be dragged over the substrate. We also calculated 
phase plots of the stance phase onset of all six legs with 
respect to the left hind leg (Fig. 4e, f). Each of the three 
leg pairs shows an antiphasic relation. The legs are more 
or less coordinated as a tripod of L1, L3, R2 and L2, R1, 
R3. Figure 4e and f show that the middle leg of one tri-
pod tends to touchdown first, and then the hind leg touches 
the ground, followed immediately by the front leg, which is 
nearly in phase with the hind leg. The data points (blue) of 
slow walks (Fig. 4f) are more spread than in the fast walks 
(Fig. 4e). This also confirms what we already know from 
the TCS analysis. The tripods are never perfectly in phase 
and the TCS improves with increasing walking speed. Nev-
ertheless, we can see how a tripod is temporally formed. 
The three legs of one tripod never touch down or lift-off 
the ground simultaneously but the temporal coordination 
improves with increasing walking speed.
In a separate analysis, we focused on walking behav-
iour during slow locomotion below walking speeds of 
30 mms−1. A continuous gait transition from tripod to tet-
rapod to wavegait coordination is proposed for hexapods 
with decreasing walking speeds (Schilling et al. 2013). 
Throughout its entire walking speed range, Cataglyphis 
fortis ants predominantly walk in tripod-fashion, which is 
also true for the runs at the lower edge of walking speeds 
(Fig. 5b). However, it seems evident that with decreasing 
speed, the tripod coordination is getting more inconsistent 
and the number as well as the proportion of other stepping 
patterns increases. We observed that ants use poorly coordi-
nated or non-tripod pattern only for a short period of time. 
Almost all ants that show tetrapod, wavegait or other unde-
fined stepping patterns during more than one step cycle, 
subsequently display the transition into tripod coordination 
within the same video sequence (Fig. 5a).
To illustrate the variability of leg coordination of very 
slow walks, we not only used the podograms but also colour 
coding and indexing of stepping patterns (see examples in 
Fig. 5a, 6.9 mms−1 with the transition from tetrapod to tripod 
Fig. 3  Walking parameters of N = 388 high-speed videos. a Stride 
amplitude as a function of walking speed for all three leg pairs. 
Leg pairs are represented in green (front legs), magenta (mid-
dle legs) and blue lines (hind legs); linear regression lines are indi-
cated, front legs: y = 0.0032 × x + 4.54; R2 = 0.28; middle legs: 
y = 0.0067 × x + 4.72; R2 = 0.66; hind legs: y = 0.0026 × x + 4.33; 
R2 = 0.20. The slope of front and middle legs differ significantly (t 
test, p < 0.05) as well as that of the middle and the hind legs (t test, 
p < 0.05) while front and hind legs are not significantly different. For 
all leg pair combinations, the y-intercept is significantly different (t 
test, p < 0.05). b Tripod coordination strength (TCS, for definition see 
“Materials and methods”) as a function of walking speed
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coordination; and Fig. 5b, 6.0 mms−1 with tripod coordina-
tion). The colour coding and indexing was also applied to 
quantify the leg coordination in all (N = 76) videos below 
walking speeds of 30 mms−1. In Fig. 5c, we give a sum-
mary of percentage values of different gait patterns. They 
show that with increasing speed, the proportion of tripod 
gait increases, while tetrapod coordination and wave gait 
decreases as well as the time where all six legs have ground 
contact simultaneously (hexa support phase). To further 
compare the individual performance, we averaged the index 
that was assigned to each frame in one video (Fig. 5d). This 
shows that with increasing speed the indices also increase, 
which reflects the increasing consistency of the tripod.
Note that a large fraction of non-tripod combinations 
forms in the transitional time from one tripod group (e.g. 
L1, R2, L3) to the subsequent one (L2, R1, L3). When we 
look at Fig. 5b, we clearly notice tripod coordination in the 
podogram, though other coordinations are also present to a 
large extent (compare Fig. 5b, colour coding and indexing 
graph). Hence, our analysis shows that even slow walking 
Cataglyphis ants preferentially employ tripod coordination, 
but with decreasing speed, the tripod gets more variable 
and other leg coordination are used as well.
We will now have a look at the swing and stance phase 
durations as a function of walking speed (Fig. 6a). Both 
the swing phases and the stance phase are significantly 
reduced at the initial part of the walking speed range. 
While the stance phases are longer than the swing phases at 
lower walking speeds, this relation reverses at higher walk-
ing speeds. Interestingly, the reversal in the hind legs and 
front legs occur much earlier (hind legs: 95 mms−1) than 
in the middle legs (middle legs: 349 mms−1). The duration 
of swing and stance phases in Cataglyphis decrease with 
increasing walking speed in the fashion of a power function 
(compare Fig. 6a) and remains more or less constant from 
a walking speed of 300 mms−1 in (Fig. 6a). For a large part 
of the range, the walking speed is increased by reducing the  
stance phase while the swing phase stays rather constant. 
At highest walking speeds, the middle legs have the short-
est swing phase and longest stance phase of all legs. Hence, 
the middle legs are the first to touch the ground and the 
last to lift-off again. We define the swing phase as the time 
where the leg is in motion, that is, the time from where the 
tarsal tip of one leg leaves the contact point on the substrate 
to the subsequent contact point on the ground. The hind 
legs displayed a peculiarity in that they often moved the 
Fig. 4  Analysis of inter-leg 
coordination. (a–d) Footfall 
patterns, podograms, of all 
six legs from four runs with 
different walking speeds, from 
minimum to almost maximum 
speed. White bars represent 
stance phases, black bars 
represent swing phases; L left, 
R right body side; 1, 2 and 
3, front-, mid- and hind leg. 
Shaded areas highlight exem-
plary tripod gait patterns with 
stance phase overlap (green, 
see b) and swing phase overlap 
(blue, compare d). Shaded area 
(grey, compare c) highlights 
an exemplary footfall pattern 
with a TCS of 0.77. Walk-
ing speeds are 6.9 mms−1 (a), 
18.9 mms−1 (b), 95.2 mms−1 
(c) and 597.4 mms−1 (d). (e, f) 
Phase plots of the stance, phase 
onset of all legs with respect 
to the left hind leg; L1, L2, L3, 
left side front, middle and hind 
leg; R1, R2, R3 right side front, 
middle and hind leg. Two exem-
plary walking speed ranges are 
shown, 560–620 mms−1 (e) and 
90–110 mms−1 (f). Blue data 
from five runs; red line mean 
vector
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tarsi along the floor without being lifted off the floor. This 
“gliding phase” is part of the swing phase, although the 
gliding hind legs that are basically dragged behind the ants 
still touched the ground. This phenomenon has recently 
been observed in Formica ants as well where the tarsi of 
the hind legs were regularly dragged over the substrate 
without being significantly raised off the ground (Reinhardt 
and Blickhan 2014). In some video sequences, we were 
able to observe that the tarsal claws were retracted before 
the gliding phase and thus the swing phase started.
Another measure for the phase relationship is the duty 
factor. Besides, it is one measure that characterises the 
dynamics of when the transition from walking to running 
occurs. It is assumed that at values of around 0.5, this tran-
sition happens (Alexander 2003). With increasing walking 
speed, the duty factor decreases linearly for all three leg 
pairs. The hind legs are the first to fall below the duty fac-
tor of 0.5 at 132 mms−1, then the front legs (at 182 mms−1) 
followed by the middle legs (at 369 mms−1). The middle 
legs are the last to reach aerial phases and thus determine 
the walking speed threshold at which the transition from 
walking to running occurs. From that speed on the ants are 
“jumping” from step to step to further increase their strides 
(compare the gaps between the triangles in Fig. 1a).
Fig. 5  Quantification of gait pattern during slow walking. Gait Pat-
tern analysis for ants walking at a 6898 mms−1 and b 5959 mms−1. 
(a, b) Podogram (above), coloured coding (middle) and indexing 
(below). Illustration details of the podograms as in Fig. 4. For the 
colour coding and the indexing we used five different classifications: 
‘tripod’ (dark-blue, 4), ‘tetrapod’ (light-blue, 3), ‘wavegait’ (yel-
low, 2) or ‘hexa support phase’ (white, 0). If none of these possibili-
ties were applicable, the frame was classified as ‘undefined’ (red, 1). 
For the list of exact leg combinations representing a typical gait see 
supplementary material. c Quantification of the N = 76 slow walk-
ing speed videos were grouped into five categories: I 5–10 mms−1 
(17 videos, 8950 frames; 27, 14, 29, 6, 23 %), II 10–15 mms−1 (16 
videos, 7376 frames; 33, 14, 22, 10, 21 %), III 15–20 mms−1 (20 vid-
eos, 7116 frames, 51, 8, 15, 6, 18 %), IV 20–25 mms−1 (14 videos, 
4284 frames; V 25–30 mms−1 (9 videos, 2423 frames; 58, 7, 15, 13, 
7 %). The percentage information in brackets after the semicolon is 
rounded and is arranged as follows: tripod, tetrapod, wavegait, unde-
fined gait, hexa support phase. d The averaged index for each video 
provide a more individual analysis of the ants’ walk. Group I differs 
significantly from group II (t test; p = 0,014); the same was true for 
group IV and group V (t test; p = 0,004). The three intermediate 
speed groups (II, III, IV) do not show any statistically significant dif-
ferences to their respective neighbouring groups
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Discussion
In 1850, the long legged desert ant of the genus Catagly-
phis was described as a “most remarkable appearance 
within the insect fauna of old world desert areas” (Foerster 
1850). With its long legs that characterise all Cataglyphis 
species, Cataglyphis fortis reaches the highest running 
speeds with values of up to 0.7 ms−1 in the literature (Weh-
ner 1983). How are these ants able to reach such high run-
ning speeds? This question was already tackled by Christop 
Zollikofer when he was a PhD student in Rüdiger Wehner’s 
lab (Zollikofer 1988, 1994a, 1994b, 1994c). His work was 
the beginning and basis of our data collections and analyses 
that we present here. With more advanced techniques, we 
were able to expand the range of walking speeds to its lim-
its and to extend the analysed parameters.
Contribution and role of the leg pairs to locomotion
The variation in stride amplitude as well as in stance and 
swing phase duration of the front legs tends to be higher 
than that of the middle and hind legs. A freer and unham-
pered positioning of the frontal tarsi is possible here 
because there are no legs in front of them with which they 
could interfere and thus limit their range in frontal direc-
tion. One could assume that the front legs generate the 
smallest forces with reference to the body movement. In 
Acheta domestica (Harris and Chiradella 1980), Carausius 
morosus (Cruse 1976) and Periplaneta americana (Full and 
Tu 1991) force measurements confirm the front leg part in 
keeping the body’s stability. The longitudinal forces of the 
protarsi act against the moving direction.
Interestingly, Zollikofer (1988) observed a higher corre-
lation of the front leg stride length with walking speed than 
that of the middle and hind legs. Moreover, he describes 
that when sprinting, the front legs of Cataglyphis bomby-
cina specimens would often not leave any tarsal imprints 
on the smoked-glass plates that he used for the stride anal-
ysis. This fact made him conclude that at very high run-
ning speeds, the ant’s front legs would stop touching the 
ground, performing a form of quadrupedalism (Zollikofer 
1994b). Loss of ground contact is well known in insects 
(Periplaneta americana: Full and Tu 1991), in crabs (Ocy-
pode quadrata: Blickhan and Full 1987) and in vertebrates 
(Heglund et al. 1974).We cannot confirm this observation 
in Cataglyphis fortis, although we analysed a large num-
ber of runs from the laboratory and the field over the entire 
speed range. Sometimes, however, when ants got startled, 
they showed a short sequence where they accelerated, ris-
ing the head and prosoma and lifted the forelegs off the 
ground. They performed a movement comparable to a 
“wheelie” known from motorbikes when their front wheel 
loses ground contact during high accelerations. However, 
we did not see this behaviour in fast running ants with con-
stant speed.
The middle legs seem to play a distinctive role in the 
locomotor apparatus of Cataglyphis fortis desert ants. They 
show the longest stance phase and the shortest swing phase 
of all legs. The middle leg of the tripod is thus the first leg 
touching down and the last lifting off the ground. Hence, 
the duty factor of the middle legs is the last to underscore 
0.5 with increasing speed and thus determines the start of 
aerial phases. At high running speeds, the tarsi of the mid-
dle legs show the most distal trace of swing and are posi-
tioned at a great lateral distance reaching over the neigh-
bouring legs without interfering with them (Zollikofer 
1988). Although this overlap happens, the legs are not 
Fig. 6  Stance and swing phase duration and duty factor. a Durations 
of stance (three shades of purple) and swing phases (three shades 
of blue) as a function of speed of all three leg pairs. Graphical fits 
are represented for middle and hind legs in purple (y = 0.22x−0.38, 
R2 = 0.75; y = 0.26x−0.41, R2 = 0.77) and blue lines (y = 1.76x−0.83, 
R2 = 0.88; y = 1.58x−0.79, R2 = 0.84), respectively. Runs without 
tripod coordination with walking speeds below 25 mms−1 have not 
been considered for these graphs. b Duty factor, which is the ratio of 
stance phase duration to duty cycle, versus walking speed for all three 
leg pairs. Leg pairs are represented in green (front legs), magenta 
(middle legs) and blue lines (hind legs); linear regression lines are 
indicated, front legs: y = −0.0005x + 0.59; R2 = 0.66; middle legs: 
y = −0.0004x + 0.66; R2 = 0.61; hind legs: y = −0.0006x + 0.57; 
R2 = 0.73. The slopes of front and middle legs differ significantly (t 
test, p < 0.05) as well as that of the middle and the hind legs (t test, 
p < 0.05) while front and hind legs are not significantly different. For 
all leg pair combinations, the y-intercept is significantly different (t 
test, p < 0.05)
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1 3
hampering each other. Further, the middle legs also per-
form the largest stride amplitude. Considering all this, we 
may conclude that the middle legs exert the biggest influ-
ence on the speed and thus on locomotion.
The stance phase of the hind legs at high walking speeds 
is very short compared to that of the other legs. This might 
be due to the fact that the hind legs display something like 
an intermediate phase where the tarsi are moved along the 
floor without being lifted off the ground. This gliding phase 
is a part of the swing phase, although the gliding hind legs 
that are basically dragged behind the ants’ body prob-
ably still provide support and thus stability, while they are 
already swung. This phenomenon has also been recently 
observed in spiders and Formica ants (Spagna et al. 2011; 
Reinhardt and Blickhan 2014). Moll et al. (2013) also pre-
sent an example of a grass-cutting ant that gains static sta-
bility by sliding hind legs during transport of load.
Stepping pattern of slow and fast walking ants
Leg coordination during locomotion is flexible and can be 
adapted according to environmental circumstances (Alex-
ander 1989). Walking speed can be one of those factors 
modulating locomotor output. With changes in walking 
speed quadrupeds, like horses, adapt their leg coordination 
to achieve an energetically optimal locomotion (Hoyt and 
Taylor 1981). Thereby, the transition from one to the next 
gait occurs in a discontinuous way. In hexapods also dif-
ferent gait types are known, but the question of gait tran-
sition has not yet been resolved (Graham 1985; Mendes 
et al. 2013). After examinations in several species, the cur-
rent understanding is that the different leg patterns are part 
of a continuum with a continuous transition from tripod to 
tetrapod to wavegait coordination with decreasing walking 
speed (Schilling et al. 2013).
Stick insects (Carausius morosus) have been observed 
to use tetrapod coordination during slow locomotion but 
switch to tripod pattern with higher speeds (Wendler 1964; 
Graham 1972, 1985). The analysis of kinematics and walk-
ing behaviour in cockroaches (Periplaneta americana and 
Blaberus discoidalis) revealed two different types of tri-
pods for locomotion, a low-speed amble and a high-speed 
trot (Delcomyn 1971; Bender et al. 2011). Fruit flies (Dros-
ophila melanogaster) prefer tripod gait during the entire 
range of walking speeds, but leg coordination also gets 
more variable with the decrease in walking speed (Strauss 
and Heisenberg 1990; Mendes et al. 2013; Wosnitza et al. 
2013). Wood ants (Formica polyctena) show stable tri-
pod coordination during the entire range of running speed 
(Reinhardt and Blickhan 2014).
Our results show that the walking behaviour of desert 
ants (Cataglyphis fortis) is in close agreement with that 
described in Drosophila melanogaster and Formica 
polyctena. Desert ants employ tripod gait as their major 
coordination pattern over the entire walking speed. This 
was also the case for very slow walks, where tripod pattern 
was generally preserved. However, it also becomes appar-
ent that during slow walks, synchrony of tripod coordina-
tion could be reduced or other non-tripod combinations, 
especially tetrapod coordination could occur, as well. This 
variability shows that Cataglyphis fortis does not need to 
rely strictly on tripod coordination and is per se able to use 
different patterns during walking.
However, the still preferred use of tripod seems to be 
kind of advantageous, probably it is an option to reduce 
errors arising from the iterative processes of path integra-
tion. The preference of tripod coordination also during 
slow walks shows that Cataglyphis ants mostly remain at 
the upper end of gait continuum proposed for hexapods 
(see explanation above). Regarding the higher variability of 
leg coordination during slow locomotion, ants scale down 
slightly from this upper end. It is conceivable that ants 
might also be able to reach the lower part of the continuum, 
yet in our investigation this was never evident.
The very slow walks rarely occur in the field. We know 
from observations that the walking speed employed during 
foraging is reached within the first two strides. To make 
the ants constantly walk below 30 mms−1 speed, we had 
to chill the environment, which in this case was a walk-
ing channel in the laboratory. Very rarely did we observe 
ants in the field in late spring and on relatively chilly early 
mornings walking at very low speeds out of the nest and 
soon back into the nest. They have never been observed to 
forage under these chilly conditions.
The quality of tripod coordination can be evaluated  
by means of a simple measure of tripod coordination 
strength (TCS) (Fig. 3b) (Wosnitza et al. 2013; compare 
also Spagna et al. 2011). With increasing walking speed, 
the TCS reaches values above 0.7 but never goes beyond 
0.85. The legs of one tripod are at a minimum 15 % out 
of phase, even at highest walking speeds with maxi-
mum stride frequencies. From a walking speed of around 
300 mms−1 on t2 and t1 of the TCS, both remain at a con-
stant level of 12–22 ms (t2) and 24–34 ms (t1). This cor-
responds to the swing and stance durations that remain 
relatively constant for these higher speeds (see Fig. 6a).  
A TCS of 1.0 might increase the chance of jerky move-
ments concentrating all impact forces of one tripod into 
one instant; especially at high speeds, there are less than 
18 ms to distribute all ground reaction forces over the con-
tact phase (compare Fig. 6a). As a result, a slight cutback of 
the TCS still assures a smooth run with maximum stability. 
The ants reach a TCS larger than 0.5 (an overlap of at least 
50 %) from very low walking speeds on, while TCS smaller 
than 0.5 only occurs at walking speeds below 100 mms−1. 
If we compare TCS of Cataglyphis and Drosophila which 
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1 3
can be between 0.1 and 0.8 (Wosnitza et al. 2013), we find 
that Drosophila at top speeds displays TCS comparable 
to Cataglyphis. Due to the wide range of walking speeds, 
Cataglyphis reaches top TCS values already at one-fifth 
of its speed range. The ants never touch ground with the 
tarsi associated with one tripod at the same time but kind 
of unroll the tripod like a ‘functional foot’ tarsal claw after 
tarsal claw. Especially at high walking speeds, the legs 
seem to act in a specific sequence. This tendency was also 
observed in Drosophila (Wosnitza et al. 2013). The alter-
nating tripods are comparable to the alternating footfalls of 
bipedal walking animals (Full and Tu 1991). The big differ-
ence, however, is that tripods engage a larger area and thus 
provide more static stability especially for slower walking 
speeds whereas at higher walking speeds static stability is 
replaced by dynamic stability (Ting et al. 1994; Zollikofer 
1994c).
How do Cataglyphis ants reach high running speeds?
Stride frequency increases in a nonlinear fashion with 
increasing walking speeds. The stride frequency levels off 
at around 30 Hz and shows a frequency plateau. From this 
point on, walking speed is increased by increasing stride 
length only. Heglund et al. (1974) described that a constant 
stride frequency can be an indicator for a change in gait. 
Small animals reach a certain speed with smaller strides 
and higher stride frequencies (Heglund et al. 1974; Zol-
likofer 1988). In the desert ants, the start of the frequency 
plateau is a first indication that the ants attain aerial phases. 
Zollikofer already presumed a frequency plateau for Cat-
aglyphis, although he did not observe one. With maximum 
frequencies of 28 Hz, the plateau was not yet evident (Zol-
likofer 1988).
Aerial phases during running are also known from cock-
roaches (Full and Tu 1990, 1991) and vertebrates (Heglund 
et al. 1974). However, this is not necessarily true for all 
animals. For instance, ghost crabs, wood ants, ostriches, 
cockroaches and the American wandering spider can reach 
a frequency plateau without aerial phases by means of 
compliant legs and the employment of grounded running 
(compare Blickhan and Full 1987; Reinhardt and Blickhan 
2014; Rubenson et al. 2004; Ting et al. 1994; Weihmann 
2013). The difference is probably due to the relatively 
longer legs of Cataglyphis, which changes the biomechan-
ics of walking. Longer legs mean larger strides in terms of 
stride amplitude and stride length. This characterizes the 
desert ants as stride length maximizers (Zollikofer 1988).
The duty factor, a ratio of stance phase to cycle period, is 
a measure that describes the transition from walking to run-
ning (Alexander 1984, 2003). At values below 0.5, swing 
phases are longer than stance phases, and thus aerial phases 
occur. Horses, dogs, ostriches and lizards reach duty factors 
well below 0.5 (Alexander 1984; Fieler and Jayne 1998). 
Cockroaches as fast-running specimens in the insect world, 
however, rarely reach such small duty factors (Ting et al. 
1994). The middle legs of Cataglyphis fortis are the last of 
the three leg pairs to fall below the duty factor of 0.5 at a 
speed of 369 mms−1 (compare Fig. 6b). At speeds between 
132 and 369 mms−1, the ants are in a kind of transitional 
phase where the front and middle legs are already showing 
aerial phases while at least one middle leg has still ground 
contact. The gait transition is not abrupt at all, which means 
that the ants probably adopt a kind of grounded running 
within quite a wide range of running speeds. Thus, the 
dynamics of Cataglyphis fortis’ locomotor apparatus seems 
to be quite similar to those of Formica worker ants and 
even similar to birds, but distinctively different from those 
of human beings (compare Reinhardt and Blickhan 2014; 
Rubenson et al. 2004).
In several insect species (Wilson 1966; Graham 1972; 
Strauss and Heisenberg 1990), stance phase duration 
becomes shorter with increasing speed, while swing phase 
duration remains largely constant; at the fastest speeds, 
the durations of both swing and stance phases equalize 
(Mendes et al. 2013; Wosnitza et al. 2013). The duration 
of swing and stance phases in Cataglyphis decreases with 
increasing walking speed and remain more or less constant 
at the upper end of the range (Fig. 6a). This corresponds 
approximately with the observations Delcomyn made in 
Periplaneta americana (Delcomyn 1971). In his obser-
vations, the swing and stance phases are reduced at low 
stride frequencies. While in Cataglyphis at lower speeds, 
stance phases are longer than swing phases, at high walk-
ing speeds the swing phases are longer than the stance 
phases. This reversal occurs for the hind legs already at 
around 95 mms−1, and for the middle legs only at much 
higher speeds of 349 mms−1. The walking speed (from 
200 mms−1 on) is increased by reducing stance phase while 
the swing phase stays rather constant.
Walking speeds of up to 0.7 ms−1 have been reported 
for Cataglyphis fortis (Wehner 1983). Although we video 
filmed in the field several times at optimal conditions, we 
never measured higher walking speeds than 0.62 ms−1. 
We believe that this is the upper limit of walking speeds 
for Cataglyphis fortis ants in the field site near Maharès, 
coastal Tunisia, which admittedly never reaches such tem-
perature extremes like for instance the Chott El Cherid in 
central Tunisia.
Why is fast running important anyway? Fast running 
helps the ants to quickly cover large areas and thus to 
enhance the chance of finding food and then back home. It 
is probably also advantageous with regard to potential dan-
ger coming from predators and enemies like robber flies, 
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J Comp Physiol A (2015) 201:645–656 
1 3
spiders, fringe toe lizards and conspecific ants (Dahbi et al. 
2008; Schmid-Hempel and Schmid-Hempel 1984; Weh-
ner et al. 1992). Hence, the ants reduce the time they are 
exposed to their harsh habitat. Long legs do not only help 
to reach larger strides and thus high walking speeds. They 
can also help to minimize heat stress (Zollikofer 1994b). 
Even slightly above the hot desert floor, temperatures 
decrease to values that the ants still can tolerate (Zollikofer 
1988; Wehner et al. 1992; Gehring and Wehner 1995).
Outlook
It seems that every pair of leg contributes in a distinc-
tive way to the ants’ locomotion. The middle legs seem 
to play a major role in gaining speed and the hind legs 
contribute in supporting stability. Nevertheless, ground 
reaction force measurement of the legs would be desirable 
to further confirm our conclusions. With higher walking 
speed, the stride frequency levels off and Cataglyphis for-
tis ants show aerial phases to expand the walking speed 
range. Each tripod group is used as a functional foot liter-
ally jumping from footfall to footfall comparable to our 
human run. Consistent tripod coordination throughout 
the entire walking speed range may be advantageous for 
the stride integrator. The occurrence of very slow walk-
ing speeds, where the non-tripod stepping patterns are 
mostly observed is usually restricted to walks inside the 
nest and the immediate surroundings of the nest entrance. 
Especially on foraging excursions, where higher walking 
speeds occur—never below 30 mms−1—robust and steady 
stepping coordination might induce errors as minimal as 
possible.
Acknowledgments We express our gratitude to Rüdiger Wehner 
for sharing his outstanding knowledge of this fascinating ant. We also 
thank Ursula Seifert for editing the text, Nadja Eberhardt, for record-
ing the very slow walks. Till Bockemühl deserves a special thanks 
for providing Matlab code for the phase shift analysis plots. Harald 
Wolf provided the high-speed camera system and supported this 
study in many ways. We are much indebted to two anonymous ref-
erees for their many valuable suggestions on an earlier version of the 
manuscript. Initial Part of this investigation was supported by grants 
from the Volkswagen-Stiftung (project I/78580) and the Deutsche 
Forschungsgemeinschaft (WO466/9-1) to H. W. Financial and infra-
structural support was provided by the University of Ulm.
Conflict of interest The authors declare that they have no compet-
ing interests.
Ethical standard All experiments comply with the current laws and 
regulations of the University of Ulm and of the country where they 
have been performed.
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution License which permits any use, distribu-
tion, and reproduction in any medium, provided the original author(s) 
and the source are credited.
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Walking and running in the desert ant Cataglyphis fortis.
Wahl, Verena,Pfeffer, Sarah E,Wittlinger, Matthias