immune to these insecticidal compounds is the zebra swallowtail butterfly (Protographium marcellus), whose larvae feed on the leaves of various species of Asimina, conferring protection from predation throughout the butterflies' lives, as trace amounts of acetogenins remain present, making them unpalatable to birds and other predators. Historical uses The tough, fibrous inner bark of the pawpaw was used by Native Americans and settlers in the Midwest for making ropes, fishing nets, and mats, and for stringing fish. Pawpaw logs have been used for split-rail fences in Arkansas. The hard, brown, shiny lima-bean-sized seeds were sometimes carried as pocket pieces in Ohio. Cultural significance Old song A traditional American folk song portrays wild harvesting of pawpaws; Arty Schronce of the Georgia Department of Agriculture gives these lyrics: He notes that "picking up pawpaws" refers to gathering the ripe, fallen fruit from beneath the trees, and that the "pocket" in the song is that of an apron or similar tie-on pocket, not a modern pants or blue-jeans pocket, into which pawpaws would hardly fit. A "pawpaw patch" refers to the plant's characteristic patch-forming clonal growth habit. Place names The pawpaw is the basis for various place and school names in the United States, almost all using the older spelling variant "paw paw". The Paw Paw Tunnel on the Chesapeake and Ohio Canal in Maryland is a 3118-foot (950-m) canal tunnel completed in 1850 to bypass about 5 miles of the 6-mile-long Paw Paw Bends of the Potomac River near the town of Paw Paw, West Virginia, all ultimately named after the pawpaw tree. In Michigan, the Paw Paw River is named for the pawpaw trees that grew along its banks. Paw Paw Lake and Little Paw Paw Lake are both tributaries to the river. The town of Paw Paw, Michigan, is located at the junction of two branches of the Paw Paw River. The Paw Paw Railroad (1857–1887) operated a 4-mile (6.4-km) rail line between Lawton and Paw Paw, in Van Buren County, Michigan. The village of Paw Paw, Illinois, was named after a nearby grove of pawpaw trees. The community of Paw Paw, Indiana, in Miami County, and Paw Paw Township in DeKalb County and Paw Paw Township in Wabash County are all named after groves of native pawpaw trees. Paw Paw, Kentucky, a community in easternmost Kentucky, was named after the native fruit tree. The (now empty) town of Paw