In the field of medicine, there’s a saying that, “If you hear hoofbeats, think horses, not zebras.” This means that although medical students will learn of a great many odd diseases, some of them are quite exotic (“zebras”), but that most patients’ complaints will resolve to common causes (“horses”).
Which of course does not mean that one won’t encounter “zebras”. Once a very great while there will be someone with the rare genetic disorder or unusual psychological glitch. Mayhap even someone with several rare genetic disorders and unusual psychological glitches! This insect profile post is dedicated to all you readers out there who are “zebras”. (Wave to the crowd folks; let them know that “rare” is not synonymous with “you’ll never meet them”.)
Like medical zebras, Zebra Swallowtails (Papilionidae: Eurytides marcellus) are rare amongst butterflies. They are not endangered, but unlike Monarchs, Cabbage Whites or Painted Ladies, you don’t see these zebras very often. This is a big butterfly, about 6-9 cm (2.5-3.5″) wide. They live in the eastern half of North America, and can be found wafting around the borders between fields and woods or streams. The reason such a large and striking butterfly lives in such obscurity is not for limitations in ecotone; it will live most anywhere but montane and alpine zones. It’s not even limited by breeding season; there are two broods in northern populations, and four broods in southern.
Rather, they are rare because the larvae are monophagous (a fancy word for “only eats one kind of thing” — a parent might lament, “My child is seemingly monophagous upon Goldfish crackers”). Well, plenty of catepillars out there are picky. But Zebra Swallowtail ‘pillars will only eat the leaves of pawpaw trees (Asimina triloba) and other species of the genus. Unlike the ubiquitous callery flowering pear trees or purple barberry shrubs, homeowners and parks managers do not go around planting pawpaws. Unacommodated by the lack of host plants, the butterflies spend their lives beyond the outskirts of the developed world. Only butterfly enthusiasts and rare fruit fanciers who go around planting pawpaws Just Because, or residents of diversified country wilds will have much hope of seeing zebras.
It’s not that medical or butterfly zebras don’t exist, but that you have to know where to find them. You also have to be willing to support their particular needs to have the opportunity to get to know them. But either one of those conditions requires understanding that zebras even exist. Yes, you might even (gasp!) have one in Your Back Yard! It’s true. And now that you have a better search image, I guarantee that you will be much more likely to meet them.