A Caterpillar Executing a Recoil and Backward Roll
Image J. Brackenbury
Caterpillars move slowly and inefficiently. They typically have all they need in front of them (food) so no need to hurry. Caterpillars that are attacked or provoked may wish to retreat more rapidly. John Brackenbury* observed the escape tactics used by caterpillars of the Mother of Pearl Moth. If poked in the head, the caterpillars would rapidly retreat using a “reverse gallop. To reverse gallop (B below), the terminus of the abdomen is planted on the ground and the body arched. All the caterpillar legs and prolegs leave the ground. The thoracic legs plant on the ground a step back from the original caterpillar position and posterior segments telescope backward in a wave. The motion can be repeated. Typically the backward movement is faster than forward movement.
Alternatively, the caterpillar may plant the terminus of its abdomen and push back strongly and rapidly. Rather than relaxing and planting the thoracic legs, the caterpillar rolls past the planted abdomen and forms a wheel that can roll backward up to five body lengths. This can be an effective escape mechanism to roll the caterpillar away from danger.
Cartoon of caterpillar movement
Left: Forward Movement
Middle: Backward Gallop
Right: Recoil and Roll
Stippling inidicates that the segmental legs are not in contact with the ground
*Brackenbury, J. 1997. Caterpillar kinematics. Nature, 1997, Vol.390(6659), pp.453-453
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