osmeterium
/ˌɑzmɪˈtɪriəm/
noun
- A forked, horn-like organ that some caterpillars (especially swallowtail butterfly larvae) push out from behind their head to release a bad smell and scare away predators.
- Kids at the nature camp learned how the osmeterium helps protect the caterpillar.
- The osmeterium releases a strong, unpleasant odor to deter ants and birds.
- When the caterpillar felt threatened, it extended its bright orange osmeterium.