Novel locomotory mechanisms in caterpillars: life-line climbing in Epinotia abbreviana (Tortricidae) and Yponomeuta padella (Yponomeutidae)

Abstract. When alarmed, caterpillars of the tortricid Epinotia abbreviana (Fabricius) and the yponomeutid Yponomeuta padella (Linnaeus) parachute at the end of a single life-line spun out by the head spinnerets.Two methods are employed to climb back up the line.The first makes use of alternate movements of the left and right set of thoracic legs, aided by side-to-side movements of the body.This results in the life-line being wound in around the third pair of thoracic legs.The second method is based on the normal peristaltic rhythm used when walking on a solid substrate.Dorsoventral curling movements gradually transfer life-line from the thorax along the succession of abdominal pro-legs to the claspers at the end of the body.The life-line has similar physical characteristics to spider orb-web silk, and a breaking force equivalent to 5–8 times body weight.The holding force of the claspers when in contact with the ground exceeds the breaking force of the life-line.These studies demonstrate the flexibility of caterpillar locomotion, when confronted with a novel situation.