Many caterpillars are camouflauged very cleverly as bird poop:

The giant swallowtail: http://www.ragamuffin.com/GST%20harness.jpg

spicebush swallowtail: http://muskogeephoenixonline.com/blogs/MollyDay/uploaded_images/spicebush-swallowtail-butterfly-caterpillar-744344.jpg

eastern tiger swallowtail: http://www.duke.edu/~jspippen/butterflies/cat070826-1710millis.rdz.jpg

viceroy: http://www.frw.ca/albums/Insects/P1030414_RJ_03_Beare_Borrowpit.jpg