Flight and flight control by the antennae in the Small Tortoiseshell (Aglais urticae L., Lepidoptera)

Summary1.Normal Small Tortoiseshells tethered to a flight mill fly up to 5 h (Figs. 1,3). Following flagellar amputation (Fig. 2), flight speed increases significantly by about 30% (Fig. 4). Increased flight speed persists when the amputated flagella are attached to the frons (Fig. 5), but normal flight speed is restored when the amputated flagella are reattached to the proximal antennal stumps (Fig. 6).2.Progressive amputation of parts of the flagella results in successive increases in flight speed (Fig. 7). Lengthening of the flagella decreases flight speed (Fig. 8). By varying its flight speed, the butterfly keeps the torque generated by drag in the pedicel-flagellum joint nearly constant over a wide range (Fig. 9).3.A strong interaction exists between optical and aerodynamic sensory inputs. Normal butterflies lacking optical orientation make only short duration flights. However, flagellarless animals lacking optical information not only fly consistently, but show a further increase in flight speed compared to those with normal optical feedback (Fig. 10).4.Flight speed (Fig. 11) and flight behavior of normal and operated butterflies were also investigated in free flight. All operations which in tethered flight are followed by changes in flight speed, lead to either a reduction or to a total loss of free flight ability.