Buy the 2015 Old Farmer's Almanac!
"Safer" has a spray that is"Safer" has a spray that is organic that works. It has BT (bacillus thuringiensis). I am not sure I can post a link so just do a search on Safer Brand Caterpillar spray. I have used it and it does work well :)

2015 Special Edition Garden GuideCooking Fresh with The Old Farmer's AlmanacThe Almanac Monthly Digital MagazineWhat the heck is a Garden Hod?