Watch: Monarch caterpillars fight for limited milkweed

Caterpillars fight for space on the same milkweed leaf. Credit: Alex Keene

Exhibiting anger while hungry is a common phenomenon — humans have even come up with the term “hangry” to describe it. In monarch (Danaus plexippus) caterpillars, when they can’t get their favorite food, milkweed, researchers have found that the usually docile creatures become aggressive, lunging at other larvae to knock them aside. After viewing this behavior in his own backyard, researcher Alex Keene, a professor at Florida Atlantic University, decided to look at the caterpillars’ behavior more scientifically. Keene and his colleagues built an open milkweed garden behind their lab. Then, back in the lab, they placed caterpillars into groups with different amounts of milkweed. They found that when there was less food, the caterpillars were more likely to push each other out of the way. This is important as at some point, caterpillars will likely encounter resource limitation. The team hopes to learn more about this aggressive response to limited food. “One of the fundamental problems with work like this is that we’re testing animals in a very derived setting. And that’s not what brains evolved to do,” Keene said. “So now that we have this invertebrate model in a relatively controlled setting, but doing an ecologically relevant behavior, that becomes important in terms of looking at the mechanism and function of this behavior in more complex organisms.”

Read the study published in iScience and watch a video of the behavior below.