I'd find a jar and poke air holes in the lid, put it and a few leaves in the jar and take him home as a pet! I'd call him Bobby and he'd be my best friend! We'd play games and I'd tell him about everything I did that day, soon he'd make his cocoon and I'd wait till he turned into a beautiful butterfly! I'd then let Bobby go so he could live out his life in freedom.
No, I could never kill such an adorable, defenseless bug. But if my life depended on it for an example, I'd give it an old fashion "DEATH BEAM!" attack, shoot a laser from my fingertip at it, between the eyes.