Kids say the darndest things. Janet Braam from Rice University was talking to her teenage son about her research on plant clocks. She had found that Arabidopsis, a commonly studied laboratory plant, produced more defensive chemicals at times of the day when insect pests were most likely to attack them. She told him that the levels of these chemicals probably rise and fall over the day, driven by an internal clock like the ones that dictate our own daily rhythms.

He said, “Well, I know what time of day I’m going to eat my vegetables!”

It was a joke, but it got Braam thinking. Shop-bought vegetables also make their own defensive anti-insect chemicals. If Arabidopsis manufactures these substances