As milkweed supplies dwindle, the insects turn up the aggression, lab experiments show
When food and space get scarce, competition can bring out the worst in monarch caterpillarKeene usually studies fruit flies and cavefish, but he decided to adapt his laboratory to study monarchs after a chance observation. “My wife pointed out in the backyard that these two monarch caterpillars were fighting with each other,” says Keene, of Florida Atlantic University in Jupiter. “I went on YouTube, and there were videos of this behavior,” he says, but for monarchs, “it wasn’t documented anywhere in the scientific literature.”
Going from a self-proclaimed “simple fly biologist” to monarch researcher, however, was a challenge. Not only did Hurricane Dorian in 2019 blow over the plants in the lab’s monarch garden, but also finding pesticide-free milkweed plants that the caterpillars would eat was harder than expected. Once the researchers overcame these challenges, though, they were able to film caterpillars competing with one another when the researchers limited the amount of available food.
