Many caterpillars employ a "masquerade" strategy, looking like various inedible items in their habitats. Here in the tropics dead leaves are a common model. To give you a sense of why this might is the case, here are a set of caterpillar-like objects that I saw today in the forest.
One of the above photos actually does have a caterpillar hiding in it. Scroll up and see if you can find it!
Hint: the caterpillar’s frass (caterpillar poo) gives it away.
You can see the little head peeking out from the top right of the hanging dead leaf in the last photo. Actually, I found 3 different individuals on the same plant, presumably all the same species of the Prepona genus (Nymphalidae). I think these are a different species from the 2 other Prepona species I have encountered here at the ACG. I will post some shots of these new guys tomorrow.
Another thing that I observed was several paired circles in the forest that were totally innocuous. Here are a few examples:
OK, I'll admit that it is a bit of a stretch to say those look like eyes. The point I'm trying to make is that there are (implicitly) other cues involved. One of the arguments used to support the idea that eyespots are mimicking eyes is that when animals see objects that even vaguely look like eyes it usually indicates a threat. Immediate retreat from anything that looks remotely eye-like should be a must for these attackers (e.g., small birds), or else they risk death (e.g., an attack from a snake). But fleeing from everything that looks remotely eye-like must also entail a cost, either energetic (quick retreat should have some energetic cost) or opportunistic (missing out on a big meal). Obviously other cues in addition to the eyespots are critical to initiate a retreat from an attacker; things like hostile behaviour that resembles an attacking or dangerous snake.