WISCONSIN:  On any given weekday in the summer, you will find me walking through fields counting bugs. In fact, it’s my job: I’m an ecologist studying the communities of insects that live in agricultural landscapes. Most days between early June and early September I drive between farms to scout crop pests and the beneficial insects that eat them, changing sticky yellow glue traps and sweeping vegetation with a canvas net.

But a single afternoon in August 2006 stands out in memory. Along one of the transects my colleague and I had set up in a cornfield, we noticed that several plants around one of our traps were missing. Strong winds or hail can knock down whole corn plants but what made this remarkable was what stood in their place: marijuana. Specifically, there were five plants, each standing about eight feet tall, in the middle of our survey plot and bursting with buds ready to harvest. While we were deciding how to proceed and what to tell the landowners, we received our next surprise; someone else was rustling through the field towards us.

When the person approaching saw us, our field gear, and our surprise, they quickly disappeared back into the dense sea of green stalks. While we never saw them (or their marijuana) again, it became clear that this was not an isolated incident. Almost every corn grower I spoke to that summer had a tale of discovering marijuana in their cornfields at harvest time. Which led me to ask: What is it about the nation’s largest crop that has made it so attractive to marijuana growers in recent years?

The answer: Growing marijuana has become possible and desirable, not to mention nearly untraceable, thanks to the very innovations that created industrial-scale, precision agriculture in the first place.