蓝蝶猿尾木（学名：Stachytarpheta cayennensis）为马鞭草科木马鞭属下的一个种。

Stachytarpheta cayennensis is a species of flowering plant in the verbena family known by many English language common names, including blue snakeweed, Cayenne snakeweed, dark-blue snakeweed, bluetop, nettle-leaf porterweed, rattail, rough-leaf false vervain, blue rat's tail, Brazilian tea, Cayenne vervain, false verbena, joee, nettleleaf velvetberry, and Cayenne porterweed. Names in other languages include honagasō (Japanese), gervão-urticante (Brazilian Portuguese), piche de gato, rabo de zorro (Spanish), herbe á chenille, herbe bleue, queue de rat (French), ōi, ōwī (Hawaiian), and tiāki (Māori). It is native to the Americas, from Mexico south through Central and South America to Argentina, as well as many islands of the Caribbean. It is known in many other parts of the world as an introduced species, including regions in Africa, India, Indonesia, Australia, Florida in the United States, and many Pacific Islands. Its distribution is now considered pantropical. In many places it has become an invasive species.