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First published online May 1, 2009
Journal of Experimental Biology 212, 1455-1462 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.025783
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Kinematics of horizontal and vertical caterpillar crawling

Linnea I. van Griethuijsen* and Barry A. Trimmer

Department of Biology, Tufts University, Medford, MA 02155, USA


Figure 1
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  		Fig. 1. (A) Forces acting on Manduca sexta in a vertical position. The caterpillar has to counteract its weight (=mg: mass times gravitational acceleration) by moving upward as well as avoid turning (torque) by pulling its body towards the substrate with the legs above the centre of mass (COM) and pushing it away with those legs below the COM. The COM is estimated to be located between segment A3 (abdominal segment three) and A4 (abdominal segment four). As the thoracic legs are believed to contribute little to gripping the substrate, the mg x/y vector on the upper body is expected to be located posterior to the thoracic legs. (B) A full crawl starts with the TP (terminal prolegs) lifting away from the substrate. Each proleg is lifted and placed forward. The proleg on abdominal segment three (A3p) touching down is defined as the end of the crawl. In this individual, a crawl lasted 2.8 s. Midswing indicates the time point at which the velocity of a proleg along the substrate is maximal. The swing phase of a proleg overlaps with the swing phase of its predecessor and its successor. (C) The swing phase for the proleg on abdominal segment A6 (A6p), starting with the start of the swing phase and ending with the start of the stance phase. (D) Anatomy of a second day fifth-instar of the Manduca sexta larva.

 

Figure 2
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  		Fig. 2. Data for A3p (prolegs on abdominal segment three) in one individual caterpillar in the horizontal orientation. (A) Velocity of A3p in the x-plane and displacement of A3p in the y-plane versus distance moved along the substrate. The timing of the maximum in velocity was used to calculate stride length. (B) Velocity of A3p in the x-plane and displacement of A3p in the y-plane versus time. The timing of the maximum velocity was used to calculate the duration of stride. (C) The displacement of A3p away from the substrate over several steps (thin gray lines) was averaged (thick dark gray line) and smoothed (black line). Proleg lift is the maximum lift of the smoothed curve. (D) The velocity of A3p along the substrate over several steps (thin green lines) was averaged (thick dark green line) and smoothed (black line). The duration of the swing was calculated at 10% of the maximum velocity.

 

Figure 3
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  		Fig. 3. A comparison of proleg lift for each proleg during horizontal and vertical crawling. The maximum proleg lift distance away from the substrate is shown for prolegs A3p (prolegs on abdominal segment three) to TP (terminal prolegs) (A–E) for caterpillars crawling horizontally (points at the left) or vertically (points on the right). Each line joins data points for an individual caterpillar. The boxplots show quartile 1 (Q1), median and quartile 3 (Q3) for all caterpillars (N=25). Outliers, indicated by dots, are 1.5 interquartile range or more removed from Q1 or Q3.

 

Figure 4
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  		Fig. 4. Timing of swing, midswing and stance of each proleg within a crawl. Onset of swing in TP (terminal prolegs) is considered to be 0% and onset of stance in A3p (prolegs on abdominal segment three) is considered to be 100%. For each proleg, the relative timing of (from left to right) the beginning of swing, midswing and beginning of stance were calculated and displayed as boxplots [quartile 1 (Q1), median and quartile 3 (Q3) for all caterpillars (N=25, 3–7 crawls averaged for each animal)]. Outliers indicated by dark gray triangles for the start of swing, light gray dots for midswing and black triangles for the start of stance, are 1.5 interquartile range or more removed from Q1 or Q3. Swing duration is indicated by the blue (horizontal crawl) and red (vertical crawl) boxes. A4p, prolegs on abdominal segment four; A5p, prolegs on abdominal segment five; A6p, prolegs on abdominal segment six.

 

Figure 5
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  		Fig. 5. Stride length (distance covered per crawl = distance covered per swing phase) as measured for A3p (prolegs on abdominal segment three) in caterpillars crawling horizontally (points at the left) or vertically (points on the right). Each line joins data points for an individual caterpillar. The boxplots show quartile 1 (Q1), median and quartile 3 (Q3) for all caterpillars (N=25). Outliers, indicated by closed dots, are 1.5 interquartile range or more removed from Q1 or Q3.

 

Figure 6
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  		Fig. 6. Timing of midswing of A3p (prolegs on abdominal segment three) within one stride of TP (terminal prolegs). Midswing TP was considered to be 0% and the next midswing of TP was considered to be 100%. The timing the midswing of A3p is displayed as a boxplot [quartile 1 (Q1), median and quartile 3 (Q3) for all caterpillars (N=25, 2–7 crawls averaged for each animal)]. Outliers, indicated by closed dots, are 1.5 interquartile range or more removed from Q1 or Q3. Horizontal crawl is indicated in blue, vertical crawl is indicated in red.

 

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© The Company of Biologists Ltd 2009