All caterpillars start out on the straight and narrow, but fall into bad ways and develop a cocoon habit.
A great pun for David Attenborough to use in his next documentary, no doubt. Okay, fine, I like it though, so he can take it or leave it. Probably leave it to be honest. It's up to you, David (I assume he searches the internet for puns based around possibly feature animals. He's got to think outside the fox. Another one for him.