I recently came across a bizarre looking caterpillar - it looked like bird poo - while looking on a wafer ash (Ptelea trifoliate) for the white, frothy "egg plugs" of the two-marked treehopper (Enchenopa binotata) and admiring some heavy potato leafhopper (Empoasca fabae) damage. I learned the bizarre looking caterpillar has an appropriately bizarre sounding common name: the orange dog.
The orange dog (sometimes called orange puppy) caterpillar is the larval stage of the eastern giant swallowtail butterfly (Papilio cresphontes). As with other swallowtail caterpillars (family Papilionidae), orange dogs sport a defense organ, called an osmeterium, that strongly resembles the forked tongue of a snake. The organ also emits a foul odor. The caterpillar normally keeps its osmeterium hidden within the segment located just behind its head (prothoracic segment). However, when threatened, the caterpillar pops out its brightly colored, foul smelling osmeterium in a dramatic display that presumably frightens predators. I've often wondered how a snake would react.
The reference guide, "Butterflies and Moths of North America" notes that eastern giant swallowtail butterflies will feed on the nectar from "lantana, azalea, bougainvilla, bouncing Bet, dame's rocket, goldenrod, Japanese honeysuckle, and swamp milkweed." However, caterpillar hosts are confined to: "Trees and herbs of the citrus family (Rutaceae) including Citrus species, prickly ash (Zanthoxylum americanum), hop tree [wafer ash] (Ptelea trifoliata), and Common Rue (Ruta graveolens). The "BugGuide" online reference notes that the caterpillars are commonly found feeding on the leaves of citrus (Citrus spp.) in the southeast U.S. Indeed, "orange dog" is in reference to the caterpillars feeding on the leaves of orange trees.
Although the butterfly is considered native to Ohio, some references note that its most commonly found in the southeast U.S. It's likely the butterfly's rarity in Ohio is a family matter: few members of the Rue or Citrus Family (Rutaceae) are native to our state. In fact, after scouring a few plant reference guides, I could find only two: the aforementioned prickly ash and wafer ash (stinking ash, hoptree, or hop tree). Perhaps readers will inform me there are others; I'd certainly like to know.
There are a number of non-native members of the Citrus family grown in Ohio landscapes including Korean evodia (Tetradium daniellii) and the Amur corktree (Phellodendron amurense). Of course, the herbaceous perennial common rue (Ruta graveolens) may also be found in our state. However, no references that I could find indicated that orange dog caterpillars will feed on these non-natives. Perhaps these non-natives are simply too foreign to the caterpillar's palate.