Narceus americanus is a large millipede of eastern North America. Common names include American giant millipede, worm millipede, and iron worm. It inhabits the eastern seaboard of North America west to Georgetown, Texas, north of the Ottine wetlands. It has a nearly cylindrical gray body, reaching a length of 4 inches (100 mm). They can be commonly found in or under decaying logs from March to October. When threatened, they sometimes curl up or release a noxious liquid that contains large amounts of benzoquinones which can cause dermatological burns. This fluid may irritate eyes or skin. Many other millipedes secrete hydrogen cyanide, and while there have also been claims that N. americanus releases hydrogen cyanide, they are unsubstantiated. They do, however, excrete a substance that causes a temporary, non-harmful discoloration of the skin known as millipede burn.

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