osmeterium
From ZooTerms (Dictionary of Invertebrate Zoology)
osmeterium (noun; plural osmeteria; Greek osme, odor): (Arthropoda: Insecta) A fleshy, tubular, eversible pouch usually V or Yshaped, sometimes arising from cephalo-dorso-meson of the prothorax of Papilionidae caterpillars, that produce a penetrating odor; also appearing elsewhere in the bodies of other forms.
