Excerpts from Jim Conrad's
from the June 13, 2010 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán, MÉXICO
The rainy season's advent engenders lush greenness, and caterpillars to eat the greenness. The sheer numbers and kinds of caterpillars is mind boggling. From one day to the next leaves of every kind, from the ground to the forest's canopy, grow more tattered. A gentle shower of sandgrain-like caterpillar poop falls everywhere, all the time. Birds alight in random places and there's a juicy worm right there waiting for them.
Among all the caterpillar types at hand I choose just one to admire and think about. It's the one shown above.
In that picture the top inset shows a much smaller, younger instar (instar being a stage of development between five or so skin-molts a caterpillar goes through), camouflaged rather like a bird dropping. The larger caterpillar below, maybe in the last instar, has abandoned the bird-dropping look for a more threatening one. If you unfocus your eyes and look from a distance, and if the disturbed caterpillar raises its front end (lower right) and waves it back and forth, as it does in real life, the banded coloring on the caterpillar's top looks a good bit like a yellowish snake with a big head and black eye, almost like a hooded viper with his head curved forward.
Bea in Ontario writes, "That caterpillar looks like it might be a swallowtail caterpillar, because of its large 'shoulders' and the colors and pattern." On the Internet we can't find a photo of the Dark Kite Swallowtail's caterpillar, the Dark Kite being our most common swallowtail, but Bea did find caterpillar pictures for the closely related Mexican Kite Swallowtail, which are almost identical to those in the picture.
Therefore, since I've not seen Mexican Kite Swallowtail butterflies here, but Dark Kite Swallowtails flit by every day, I'm guessing that the caterpillar in the picture is a Dark Kite Swallowtail.