Caterpillar of the day: Caligo atreus

Caligo atreus (Nymphalidae)

I observed this species when I was at the San Gerardo station in the ACG. Until this one I had never seen anything like it. This specimen was a 6 cm long pre-ultimate instar. 

Late instar Caligo atreus caterpillar
Late instar Caligo atreus caterpillar

Late instar Caligo atreus caterpillar
The head almost looks like a tribal mask doesn't it? The caterpillar body seems to match the leaf of its host plant fairly well. I suspect that it uses those menacing-looking spines on its head as a club to swing towards attackers when it is harassed. But, the most interesting part of this species is its pupa. I would love to see the pupa of this species becasue it may be protected by a form of snake mimicry too. Here are some photos of the pupa from the ACG caterpillar database:

Close up of Caligo atreus chrysalis. Photo: ACG caterpillar archive 
Caligo atreus chrysalis, side view  Photo: ACG caterpillar archive 
Caligo atreus chrysalis, dorsal view. Photo: ACG caterpillar archive 
The pupa of this species can be over 5 cm long! The pupa's shape does resemble the head of a viper, and the white spots are roughly in the right place if they were mimicking snake eyes. But could just a head be enough to intimidate predators from attacking? Probably, especially if attackers do innately avoid things that looks like a dangerous snake. Further, the head and eyes are probably the most salient cues used by other animals to indicate that they are dealing with a threat. If the little spots don't increase the pupa's conspicuousness much and ward off attackers even part of the time then it is at least conceivable that these spots evolved as a form of eye mimicry.

Most of the other instars look like my photos above, but as in many species the ultimate instar has darker colouration. Here is a photo again from the ACG caterpillar archive:

Photo: ACG caterpillar archive


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