AbstractLacewings launch themselves into the air by simultaneous propulsive movements of the middle and hind legs as revealed in video images captured at a rate of 1000 s-1. These movements were powered largely by thoracic trochanteral depressor muscles but did not start from a particular preset position of these legs. Ridges on the lateral sides of the meso- and metathorax fluoresced bright blue when illuminated with ultraviolet light suggesting the presence of the elastic protein resilin. The middle and hind legs were longer than the front legs but their femora and tibiae were narrow tubes of similar diameter. Jumps were of two types. First, those in which the body was oriented almost parallel to the ground (-7 ± 8 degrees in green lacewings, 13.7 ± 7 degrees in brown lacewings) at take-off and remained stable once airborne. The wings did not move until 5 ms after take-off when flapping flight ensued. Second, were jumps in which the head pointed downwards at take-off (-37 ± 3 degrees green lacewings, -35 ± 4 degrees in brown lacewings) and the body rotated in the pitch plane once airborne without the wings opening. The larger green lacewings (mass 9 mg, body length 10.3 mm) took 15 ms to accelerate the body and the smaller brown lacewings (3.6 mg and 5.3 mm) 9 ms, to mean take-off velocities of 0.6 and 0.5 m s-1. During their fastest jumps both green and brown lacewings respectively experienced accelerations of 5.5 or 6.3 g, required an energy expenditure of 5.6 or 0.7 μJ, a power output of 0.3 or 0.1 mW and exerted a force of 0.6 or 0.2 mN. The required power was well within the maximum active contractile limit of normal muscle, so that jumping could be produced by direct muscle contractions without a power amplification mechanism or an energy store.