Here's a pure guess:
The comma's legs and antennae are the biggest giveaway. If a potential predator happens to be looking in the direction of the comma, perhaps the white mark, which doesn't spell 'butterfly' or 'food' in any obvious way, draws its eyes away from the legs and antennae, like a decoy. The predator checks out the white mark, sees nothing special to eat, and moves on.
![Image](http://www.guypadfield.com/images2007/calbum079.jpg)
Without the distraction of the comma, wouldn't all those appendages be more readily noticed?
Just a thought.
Guy