An eyespot that “blinks”: an open and shut case of eye mimicry in Eumorpha caterpillars (Lepidoptera: Sphingidae)

We describe the final instars of two tropical Sphingidae caterpillars – Eumorpha phorbas and Eumorpha labruscae – from Area de Conservacion Guanacaste, northwestern Costa Rica, whose anal horn has become a posterior eyespot structure capable of rapid palpitation. When approached or harassed, the caterpillars palpitate this eyespot and produce the effect of a blinking vertebrate eye. We propose that this “blinking” is an extension of eye mimicry or at least draws attention to the eyespot, functioning to startle or intimidate would-be predators. As snakes lack eyelids and do not blink, this suggests that the blinking eye represents a more generalized (or possibly mammalian) eye. Eyespot “blinking” is probably controlled by the same musculature used to wave the anal horn in earlier instars. The extent to which this eyespot is perceived as a blinking eye, and the degree of protection from the caterpillars’ suite of potential predators, remain to be discovered.