So here’s the deal, I’m off on my morning walk and have gotten maybe 100 yards from home when I’m stopped dead in my tracks by a small clump of fennel between the sidewalk and a phone pole. Do I pull it up, as I’ve done hundreds of times with this invasive plant, tasty though it is? I think back to the dozens of hillsides, fields and little pockets where good habitat for rare birds and butterflies was being crowded out by the stuff, and that I and other volunteers had helped clean out. Or tried to. Fennel has deep roots and is hard to get rid of. You can’t just top it and it goes away.

But no, this clump, there because of its invasive nature, was not a threat to anything. In fact, what stopped me was not the plant so much as what was crawling all over it—dozens of caterpillars. The smaller ones were little black and white tubes looking like so many bird droppings. The larger ones were lovely yellow-dotted creations with black and green bands defining each body segment, and when I stroked them, they reared back, extruding an orange Y from their heads. The osmetrium—a stink gland to drive off parasitic flies and wasps! Who would have thought? Nature at its best.

Each caterpillar was destined to become an anise swallowtail butterfly, a black and yellow beauty once it emerged from its chrysalis after a few days rearranging all its parts during its pupal phase. That change is one of the greatest wonders of nature, too. Somehow, this eating machine, the caterpillar in front of me busily munching away and digesting the tough cellulose of the fennel plant has to develop reproductive organs, grow wings, sprout long legs from the stumps it now has, and completely redo its digestive system and mouth machinery to take in and digest the sugars in the nectar of flowers. And do it quickly. It takes us fifteen or twenty years, and preferably more, to reach sexual maturity. These bugs do it in that many days. Wild stuff!

So here I am, bending over this fennel plant searching through the filamentous leaves. Ah, there’s another big caterpillar down there. And that’s a first instar, so small it’s barely visible—five more instars to go with a molted skin between each before it pupates! With people passing by on the sidewalk wondering what is that guy doing? But they don’t stop to find out. Well, maybe they’ll read this. Probably not. Hah! There’s another, and I go on looking for more.