Papilio zelicaon Cannibalism

Today we learned just what a confused newly molted anise swallowtail (Papilio zelicaon)  larva can be capable of. . .

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We have always noted that in insect species where cast off cuticle is routinely eaten, there is some sort of psychological change that occurs immediately after molting that prompts them to look for the skin, recognize that it is skin, and eat it. The behavior seems purely instinctive. We have found, with observational experimentation, that putting skins at the mouth of these newly molted insects creates an automatic response to feed on it. The skins need not be its own. 

Today, we were playing around with a newly molted anise swallowtail (Papilio zelicaon) fifth instar that had not yet eaten its skin. We carefully placed the skin at its mouth to prompt it to start feeding on it while it was still in the "skin-eating mode". After it finished the skin, we continued to place more skins left behind by a few of the other larvae that molted. As long as we kept putting more skin there, it continued to feed, thinking that it still had not finished. It appeared to like the stuff very much. . . it is probably quite nutritious. 

Eventually, after finishing its fourth skin, we got a sick idea to try to see if it would be also willing to feed on larvae. We had a lot of first instars on hand that we thought couldn't be much different than the skin that it was already eating. The main other constituents are blood, which is obviously edible (in fact, injured larvae instinctively look for the blood to try to drink it up), and gut which contains partially digested food matter and fluids (which disturbed larvae sometimes regurgitate and then drink back up) and is also edible. Both of these things should actually be in more easily digestible forms than eating leaves and would probably be more efficiently assimilated by the body. This and many other reasons are why cannibalism is so great among meat-eating organisms and why meat is more nutritionally viable than plant matter. 

We put the first instar onto a skin and got it to start eating the skin first. When it got to the first instar, the first instar started thrashing around violently as it was getting attacked and the fifth instar backed off. Eventually, however, it started biting through the first instar from its end (the head capsule is difficult to bite) and ate the whole thing happily. . . We're not sure if it even realized. After that, we gave it another one, along with a sixth skin, which is also ate. Perhaps it will have some strange poops after this meal. 

After the second first instar, it started to lose its appetite and we put it back onto the fennel. Obviously, it would not be a good idea to try to sustain it only on skins and larva and it would most likely reject them once it gets out of the skin-eating mode. But this was still an amusing (okay, maybe more disturbing than anything else) experiment. Perhaps this larva will perform better than it would have if it hadn't eaten all this stuff.

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Authors
Brian Liang

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