My kids don’t like wasabi very much. They’re not keen on mustard either, which is exactly what this family of plants is hoping for. The strong flavors derived from the plants in the order Brassicales, including cabbages, horseradishes, mustards and kale, aren’t supposed to taste good, particularly to cabbage butterflies (pieris rapae). The fact that humans chose to enjoy what was supposed to be a fierce defense system is just a reminder of how narrow a niche some adaptations end up being.
Brassicales’ ‘flavor-as-bug-repellant’ development started over 90 million years ago. Ancestors started growing glucosinolates, chemicals that are toxic to insects. This way the plant could grow without being completely consumed by cabbage butterfly caterpillars. Those hungry caterpillars then had to either find something else to eat, or come up with way to enjoy the dangerous plants.
The caterpillars that started producing a glucosinolate-defusing protein lead the next charge in this little arms race. The advantage was two-fold: they could not only eat Brassicales again, but they were the only insects left to do so, meaning they now had them as their own private buffet. So the plants had scared off most insects, but intensified their value to these caterpillars all the more. The response was new branches in the plant family tree, using different amino acids to make the caterpillars’ defensive-proteins obsolete.
This cycle continued over and over, leading to new, specialized species along the way. In response to their local caterpillar threats, plants ended up creating new flavors along the spectrum of “bitter” and “burning.” These defenses technically work on humans too, since that’s the source of the flavors we enjoy when eating these plants, but in application they’re not actually a threat to us.
Enjoying our position from the sidelines
My kids may still fall for kale or wasabi’s trick, and feel like it’s not safe to eat (often along with a resounding “yuck!” or “it’s spicy!”). Despite my enjoyment of these foods, I have to allow for these reactions to an extent, since bitterness is generally associated with toxins. But once you get past that, you can discover that these defensive plants have really just made themselves more delicious. Thankfully, our ability to selectively breed crops at this point should save us from the caterpillar’s struggles with potentially toxic wasabi down the line.
Source: Why You Should Thank A Caterpillar For Your Mustard And Wasabi by Jessie Rack, The Salt