Watson's Dutchman's Pipe or Southwestern Pipevine (Aristolochia watsonii) grow along desert washes and in upland areas here in Tucson. These sprawling vines are not easy to find because they are fairly small, have dully-colored leaves and flowers, and are often hidden in a tangle of other plants. The easiest way to find Watson's Dutchman's Pipe plants is to look for the orange and black Pipevine Swallowtail (Battus philenor) caterpillars that eat them.

After I discovered a Pipevine Swallowtail caterpillar crawling around in Molino Basin Campground, I knew that Watson's Dutchman's Pipes must grow there because these caterpillars only feed on plants in the genus Aristolochia, and this is the only one found here in Arizona. I found this Watson's Dutchman's Pipe at Molino Basin Campground thanks to the caterpillar.

Watson's Dutchman's Pipes have strange looking brown and green flowers, and their method of pollination is even stranger. The flowers have a peculiar musty smell, similar to that of the inside of a rodent's ear. Like a rodent's ear, the open flower mouth is elongated and lightly haired. The flower's rodent ear smell and appearance attracts small, bloodsucking flies that like to feed on the tender, exposed skin on the inside of a rodent's ear. When the flowers close for the night, some of the flies are trapped inside. The trapped flies buzz around inside the flowers and become covered in pollen. If those pollen-covered flies are fooled again by a different Watson's Dutchman's Pipe flower, they will pollinate it.

Although these plants have been used medicinally in the past, they are extremely poisonous with potentially dangerous side effects. The Pipevine Swallowtail caterpillars that feed on them absorb the toxins, and they themselves become highly toxic. These voracious caterpillars will not only eat the leaves, they will also chew into the fruits, which are also toxic.