This week I took a trip to the University of Maryland to give a talk about parasites. I waxed poetic about how sophisticated parasites are in their manipulations of their hosts, and how we might do well to learn from their wisdom about how the brain works. At dinner, I sat next to David Inouye, the incoming president of the Ecological Society of America. The waiter set down plates in front of us, loaded with plants, animals and fungi–free-living organisms, in other words. As we looked at the plates, a question came up: is there a parasite you can eat?

Obviously, no one sits down to a piping hot bowl of smallpox soup. But parasites can also take the form of plants,