![]() Butterflies spent a minimum of 30 min in the incubator before being used in trials to ensure sufficient cooling. ![]() When not in flight or used in experimental trials,butterflies were kept in a dark incubator (Termaks KB8000, Bergen, Germany) at 8☐.1☌ to minimize weight loss, reduce activity and stress level,and to facilitate handling. Butterflies were kept in the flight cages for 3 h on the capture day and for 1 h the day after capture, which was also the day that they were subjected to trials. The flight cages were placed 0.4 m from a south-facing window with additional light provided by two Philips Powertone HPI-T Plus 400 W light bulbs (Stockholm, Sweden) in the ceiling. To achieve variation in food load, half of the butterflies were also provided with a 10% sugar solution. The adult Aglais urticae (Linnaeus 1758) butterflies used in this study were wild caught between the 25th of August and 1st September, 2005, in the vicinity of Tovetorp Zoological Research Station, located in southeast Sweden (58★6′N 17☀8′E) and kept in indoor flight cages(0.65 m × 0.65 m × 0.70 m) provided with moist paper towels to prevent dehydration. Finally, this study shows that FMR affects take-off angle and sinuosity, with steeper angles and more turning in butterflies with low FMR. ![]() Furthermore, our study suggests, for the first time, that butterflies may experience impaired escape ability after feeding, which directly leads to a decrease in FMR a reduction from 0.5 to 0.3 reduced escape flight velocity by about 37% at 0.5 m from the start. The results show that butterflies that were subjected to a simulated predator attack flew at higher velocities and straighter than butterflies that were allowed to take off spontaneously. ![]() Here we tested whether the flight performance of an insect, the small tortoiseshell butterfly ( Aglais urticae), is affected by variations in body mass due to feeding by comparing flight performance parameters between individuals that (i) took flight spontaneously or after being subjected to a simulated predator attack and (ii) varied in flight muscle ratio (FMR: thorax mass/total body mass). Previous studies on reptiles and birds have revealed that gaining weight, due to for instance egg load or lipid accumulation, leads to impaired escape ability and possibly increases the risk of being caught by predators. ![]() For an animal to escape an attacking predator, speed and manoeuvrability are likely to be crucial factors. ![]()
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