http://www.schneier.com/blog/archives/2009/12/plant_security.html
Very cool -- apparently, when plants are being eaten by, for example, a caterpillar, they'll release chemicals that attract both dragonflies and parasites, both of which will feed on the caterpillar.
This is the entire plot of the movie The Happening. Only instead of caterpillars, it's humans, and instead of dragonflies, it's suicide.
My friend had an interesting comment: the article doesn't mention fruit-bearing plants, which *want* to be eaten (in order to spread the seeds), and that doesn't die (or get harmed) when that happens.