I found this beauty when I pulled most of my bolting fennel out of the garden. Fortunately I found it before I pulled all of the fennel out so it still has something to dine on. At the rate it's eating it may run out of food before it pupates.
You can watch a much better quality video here, click on the gear wheel at them bottom of the video and chose one of the HD files.
Be sure to catch both ends in action at about 5 seconds into the video, it can eat and poop simultaneously. It's fascinating to me how it reaches for the very end of a frond segment and then munches down to where that segment joins another segment, then it reaches to the end of another segment, and so on until it munches all the way to the main stem. Not one segment of the leaf falls and goes to waste.
This baby is one of the larval stages of an Anise Swallowtail butterfly. It can eat all the fennel remaining in my garden. I just hope that I can watch it emerge as a butterfly one of these days.