This caterpillar was found on the base of a tree along the Tiger Fern trail, Cockscomb Basin Wildlife Sanctuary, Belize. When lying on a twig or trunk, it is excellently camouflaged. When disturbed, the caterpillar is renowned for resembling a viper. It raises the anterior end of its body, rotates the front third to half about 180 degrees and flattens its thoracic legs against the body (Miller et al., 2006), expands the tip to a triangular shape (Caillois, 1964, called it the caterpillars “mask”) by contracting its first three segments and expanding the fourth, and looks exactly like a viper (purportedly an eyelash viper, Bothriechis schlegelii), replete with “eyes” (round dark spots) and krinkles in the skin that look like scales. It even sways and “strikes” at its potential predators as a snake might.
These animals, both caterpillars and adults, are rarely seen in the wild. Their favored food plants are abundant, with a known food plant for the caterpillar in Belize being yemeri trtees (Vochysia hondurensis), but their survival strategy definitely involves crypsis and presumably rarity. Their adult is a sphinx (hawk) moth that is beautifully patterned in shades of brown and black, making them cryptic in the leaf litter in which they hide during the day.
Google the scientific name (also for the related genus Hemeroplanes) for nice photos of the viper mimic form described herein.
Caillois, Roger. 1964. The Mask of Medusa. Northumberland Press Ltd., Gateshead on Tyne, UK. 127 pp.
Miller, J. C., D. H. Janzen, and W. Hallwachs. 2006. 100 caterpillars. Portraits from the tropical forests of Costa Rica. The Belknap Press of Harvard Univ. Press, Cambridge.