This week I had the unique chance to observe the monarch caterpillar in its natural habitat, which is to say the massive combination nursery-buffet of the milkweed leaves they hatched on. Monarchs are in this part of the world one of the quintessential butterflies of popular knowledge, in part because of the beauty in their seemingly unmistakable orange and black colors, in part because of their commonality in the region, and in part because of the notable physiological niche they’ve created in the butterfly world. Poison caterpillars are not terribly uncommon; it’s one of the big three ways the butterfly family stays off the menu – poison, pretending to be something inedible (bird droppings, anyone?), and good old-fashioned hard-to-spell camouflage. The monarch and a few of its evolutionary relatives eat exclusively milkweed leaves because the milkweed is poisonous, and they can store the poison inside their bodies through the rest of their life cycle, dissuading birds from coming for dinner. But there are also other butterflies in the family – namely the queen and the viceroy butterfly – that wear the orange and black “don’t chew on me” badge of their royal cousin. They’re mimics, and for a long time were textbook examples of Batesian Mimicry, wherein a harmless creature evolves to look like a not-so-harmless creature to fool predators. It’s since been elucidated that viceroys and queens can also be unpalatable, making theirs an example of Müllerian mimicry instead. That the viceroy probably tastes like an aspirin due to its diet of willows and poplars was such a bitter pill to swallow for the entomological community that the tale is still recounted in Ecology textbooks today, or at least two years ago, if my somewhat informed opinion didn’t give it away. At any rate, the monarch is the one who consistently eats the foul stuff, where as its relatives have a bit more range to their appetites. So when it comes to giving predators upset stomachs, the monarch is the genuine article.

A vertebrate also spoke to me about bodily poison this week, one Scott Russell Sanders, in his essay on growing up on a military base. There was some (perhaps intentional) irony in a man who played in an ammo dump insinuating I may develop cancer from living on the same planet as a working nuclear device, but if a child of the Cold War wasn’t generously wary of nuclear weapons I’d be concerned he wasn’t paying enough attention. However: there was one point I must admit I disagreed with Mr. Sanders on. He bemoans the fence locking both him and nature inside the stifling atmosphere of one of the most abhorrent times to be an American citizen. But he only lightly acknowledges the fact that the fence is the only reason the nature is still there. For what was his childhood playground if not a crudely rendered national park, a wildland where interlopers faced federal prosecution? That the chain-links and machine guns were there to protect stores of death didn’t stop the fact that they also protected the life inside. Behind the walls of the arsenal the trees and animals were able to recolonize their stolen land from the farmers that came before. His home offered him a chance to view nature’s slow victory over humanity, a “terrifying comfort” my generation no longer has the chance to feel due to the inaction of the previous one.

This brings me back to the caterpillars. It may seem like a miserable existence, but those 60 square feet of leaves that comprise the monarch’s world here at the farm are a haven. In that field they are protected from further habitat destruction. In this case it’s a rare upside to habitat fragmentation, in that there’s still any habitat left at all. The fence goes both ways.