Many animals have a fake eye — or eyespot — or two that they can use for protection from predators, often by frightening or distracting the hungry creature. Eyespots are especially common among tropical caterpillars. And researchers conducting a caterpillar inventory in Costa Rica have documented two species (Eumorpha phorbas, above, and E. labruscae) in which the eyespots can sort of blink. They report their findings in the Journal of Natural History.
How can an eye that’s not real blink? To find out, Thomas J. Hossie of Carleton University in Ottawa, Canada, and colleagues collected and reared caterpillars of the two species. When each species reaches the last instar before turning into a moth, it takes a form that has an eyespot on a tentacle that pops up from its butt; this is known as the anal horn. For the study, the researchers would remove a caterpillar from its rearing bag, let it acclimate for a minute, and then prod its rear three times. The result was a “blink,” such as the E. labruscae captured in the video below:
“Both caterpillars can ‘blink’ their posterior eyespot upon perceiving a threat,” Hossie writes on his blog Caterpillar Eyespots. “That is, they can move the skin around the eyespot such it either conceals/reveals the eyespot or flashes (i.e. reflects light) conspicuously towards an onlooker.”
Being able to blink the eye would make it look more like a mammal or bird eye, which is a little odd because scientists had thought that the eyespots on caterpillars were supposed to look more like snake eyes. Snakes can’t blink because they don’t have eyelids. Unfortunately Hossie and the other researchers haven’t been able to test how predators respond to these distinctive eyespots — including whether they might interpret them as mammal, bird, or snake — because these are really rare species.
But Hossie notes on his blog that these caterpillars have another defensive trick that is truly snakelike: “Interestingly,” he writes, “both Eumorpha caterpillars also inflate their thoracic body segments, while pulling their head into their body, to form a diamond shape which appears similar to the head shape of dangerous co-occurring snakes (at least to human observers).”
Image copyright CAPEA, used with permission under Creative Commons license