Tiger Swallowtail: Papilio gluacus
Black Swallowtail: Papilio polyxenes
Spicebush Swallowtail: Papilio troilus
Tiger swallowtails are tricky. Even in areas where the adults fly in abundance I may fail to ever find a caterpillar. But if I really need a tiger, I can get one. Like going to a specialty store for a hard to find item, there is a row of cherries in Princeton, a sapling poplar in Gardner, and an ash tree in the blue hills, that rarely let me down.
A tour of local farm-stands and nurseries will usually provide me with black swallowtails. Most farmers welcome me as the "caterpillar guy", letting me pluck off swallowtails from carrot, parsley and dill. They usually want me to take some hornworms too. Who am I to refuse?
Spicebush swallowtails are easy if you know their trick. Sassafras is good for more than making tea. From yards away I can see the upwardly curling leaf shelters. Gently pulling open a shelter, I find New England’s premiere snake-mimic staring up at me with pouting fake eyespots.
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This image compares Massachusetts’ three native swallowtail butterflies.
At the top, a tiger swallowtail caterpillar has recently undergone a color change from bright leafy-green to dingy bark-brown. This type of color shift is performed by many caterpillar species as they prepare to leave their leafy homes and set out on a cross-country trek over tree trunk and leaf litter, in search of a suitable place to pupate.
In the middle, a black swallowtail caterpillar has extended its bright orange inflatable horns, or osmeterium, in a defensive gesture. The sudden appearance of these horns is surprising, as is the blast of noxious smells that accompanies their inflation. All three swallowtails have osmeterium, but they are often shy about using them, especially in front of my camera lens.
At the bottom, a spicebush swallowtail hides beneath the guise of its predator’s predator. The large fake eyespots are enough to make an inquiring bird nervous, but those who see past its disguise often describe this fearsome snake-mimicking caterpillar as cute.
Strip away the colors, patterns, and textures that define each swallowtail caterpillar and what remains are three remarkably similar forms. Short bodied and fleshy, with enlarged necks and downward facing heads, the basic morphology of the three species is nearly identical. It is the dress of defensive adaptations that makes each species unique, each one special.
The three swallowtail caterpillars feed upon very different host plants, live in different habitats, and face different predators and parasitoids. The differences between them have directed their evolution in independent directions. Each swallowtail species, its canvas remaining largely consistent, has been painted, sculpted, and costumed, to best fit the details of its own life history.
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