A strain of German cockroach is intolerant to glucose, helping the pests to avoid sugar traps and glucose-laced poisons. Scientists at North Carolina State University tested "regular" cockroaches alongside the mutated strain by giving them a choice of glucose-heavy conserve and peanut butter. While the regular cockroaches showed no preference between the two treats, the mutated insects swarmed the peanut butter. When some attempted to eat the preserve, they immediately jolted back. Magnified footage shows the cockroaches actively spitting out the glucose.
Dr. Coby Schal, who leads the appropriately-named Schal Lab at the university and co-authored a paper on the experiments, explains the mutation. "The cells that normally respond to bitter compounds were responding to glucose in these [mutant] cockroaches," Schal told BBC News, comparing the glucose-aversion to "a baby that rejects spinach." The behavior was first spotted in the mid-90s, but it's only now that we have an understanding of how it developed.