Is that a snack or a snake? To small tropical birds foraging on the rainforest floor, those two scowling eyes peering back at them from between the leaves could be a predator. But they also could belong to one of the hundreds of caterpillar species that have evolved eyelike spots and patterns to trick feasting birds. By impersonating a snake or other predatory reptile emerging from the shadows, these caterpillars startle their adversaries into fleeing.
The caterpillar patterns don't need to be highly detailed to work. Even the mere suggestion of eyes is enough to shoo a bird away, suggesting the birds are reacting to hard-wired, predator-avoidance instincts, researchers report  online today in the Proceedings of the National Academy of Sciences.
In this slideshow, you can view a selection of some of the images the researchers collected  as part their 30-year survey of more than 5000 rainforest caterpillars in the Area de Conservación Guanacaste in northwestern Costa Rica. The pictures highlight the many tactics that caterpillars use to steer clear of ending up in someone's belly.
A previous version of this slideshow stated that the first image featured a caterpillar's back end when it was actually its front and that the second image featured two caterpillars when it actually featured a single pupa. The captions have been corrected.