The hardy insects have always been attracted to sugar, which offers them an intense boost of energy, so in the 1980s, exterminators began using glucose as bait in insecticide traps. But within a decade, the traps stopped working. Now, entomologists at North Carolina State University have figured out why. Cockroaches have nerve cells on hairs all over their body that detect tastes and send electrical signals to the brain saying whether the substance they’re touching is sweet and edible, or bitter and potentially dangerous. Now, when most cockroaches taste sugar, they “jump back as though you’ve given them an electric shock,” study author Coby Schal tellsTime.com. Researchers think that when humans started killing roaches with sugar-laced poison, natural selection encouraged the survival of roaches that were repulsed by sugar because of a rare mutation. Over time, as sugar-loving roaches died off, roaches with the mutation became the norm.
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