Some people are hungry when they’ve missed a meal or eaten too little of one. Some people get “hangry.” That’s when your blood sugar dips too low and makes you seriously irritable. (Hangry = hungry + angry.)
Humans aren’t the only animals who feel hangry. New research from scientists at Florida Atlantic University shows that monarch caterpillars do, too. When these normally gentle, two-inch-long insects don’t get enough of their main food — milkweed — they turn into jerks. They butt heads. They lunge at each other. They knock each other out of the way.
“Our brains are set up to control our functions. And one of the most important functions, whether you’re a caterpillar or a human, is to find food,” says Alex Keene.
Keene is a neuroscientist and the lead author of the study. He says that the urge to fight when food is scarce may be the same for people and insects. The difference: “We can process that we shouldn’t hit people. But caterpillars can’t.”
Keene says he’s always loved monarchs — some populations of which, in the butterfly stage, migrate thousands of miles. When they’re caterpillars, “they’re so charismatic, they look like they have two heads; they’re huge for caterpillars, and they interact socially,” he says. He was inspired to study them after seeing them shove each other in his garden. He looked for information on the Internet. “But I couldn’t find a [scientific] paper on caterpillar aggression,” he says. “Then I went on YouTube and found lots of videos.” That convinced him that caterpillar aggression is real.
Keene and fellow scientists captured monarch caterpillars in the wild and placed them on milkweed leaves in their lab. Groups that had plenty to eat were calm. Groups that didn’t turned aggressive. The most aggressive caterpillars were the oldest ones, which were almost ready to metamorphose into butterflies. (They don’t eat for eight to 12 days while they’re in a chrysalis.)
Habitat loss across the United States is leading to a loss of the milkweed that monarchs need to survive. Even outside Keene’s lab, the caterpillars are probably getting hangry. But that’s not the primary reason he wants to study them. He hopes to gain a better understanding of how hunger affects aggression in humans. It’s a lot easier to study it in caterpillars.
“The human brain has billions of neurons,” Keene says. (Neurons are sensory cells that take in information, then send signals to our brains.) Insects have only “100,000 or 200,000 neurons, so we can get to a point where we can understand what each cell does. That would be completely impossible” in humans’ larger brains.
Share this articleShareThis study was the first step. Next,Keene will set up cameras in a garden on campus so he can film monarchs. He’ll also start to study their genes in the lab to see which ones are involved in hunger-related aggression.
Many nonscientists, it seems, are eager to help. Since his paper was published, he said, “I’ve gotten videos from people all over the country, showing monarch fights.”
Correction: An earlier version of this story incorrectly stated that monarchs are in a cocoon during the stage between caterpillar and butterfly. They are in a chrysalis. The story has been updated.
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