Bird Poop Caterpillar

Well it looks like bird poop but I found a couple of these on our balcony citrus tree. They are of the Giant Swallowtail butterfly and are supposed to be NOT so good for citrus trees but I didn’t have the heart to destroy them since there are only two, and they didn’t appear to actually be harming the tree. Me and my boys watched them for a few days and then poof, they were gone. Have no idea where the ugly little suckers went.