Recently I have noticed a lot of caterpillars that look like bird poop. I believe they are called Papilio cresphontes. These have basically killed one of my lemon trees. How can I get rid of them organically. I have hand picked as many as I could off the leaves but I'm sure there are still a lot of them on the lemon tree. This is how they look
http://www.youtube.com/watch?v=DRfnbCno-9o
http://www.youtube.com/watch?v=DRfnbCno-9o