Jumping mechanisms in adult caddis flies (Insecta, Trichoptera).

Abstract

To understand the jumping mechanisms and strategies of adult caddis flies, leg morphology and movements were analysed in three species with mean masses of 3.9 to 38 mg. Two distinct jumping strategies were found. First (67% of 90 jumps), take-off was propelled solely by the middle and hind legs while the wings remained closed. Second (33% of jumps), the same leg movements were combined with wing movements before take-off. The hind legs were 70% and the middle legs were 50% longer than the front legs and represented 105% and 88%, respectively, of body length. Both hind and middle trochantera were depressed together, approximately 15 ms before take-off. The front legs apparently did not contribute to thrust in either strategy and were the first to be lifted from the ground. The hind legs were the next to lose contact, so that the middle legs alone provided the final thrust before take-off. Jumping performance did not differ significantly in the two jumping strategies or between species, in acceleration times (range of means for the three species 14.5-15.4 ms), take-off velocities (range 0.7-1 m s(-1)) and trajectory angles. A significant difference in jumps propelled only by the legs was the lower angle (9.3 ± 1.9 deg) of the body relative to the horizontal at take-off compared with jumps involving wing movements (35.3 ± 2.5 deg). Calculations from the kinematics indicated that jumps were produced by direct muscle contractions and did not require power amplification or energy storage.