bombardier beetle

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various beetles of the genus Brachinus and related genera that expel an acrid, volatile secretion from the abdomen when disturbed, making an audible sound.

Century Dictionary and Cyclopedia

1. n. The common name of many coleopterous insects, family Carabidæ and genera Brachinus and Aptinus, found under stones. When irritated, they are apt to expel violently from the anus a pungent, acrid fluid, accompanied by a slight sound.

Wiktionary

1. n. A beetle whose defence mechanism enables it to eject a hot aqueous mixture of chemicals at predators. They come from a number of subfamilies: Carabinae (e.g., Brachinus crepitans), Metriinae (e.g., Stenaptinus insignis) and Paussinae (e.g., Goniotropis nicaraguensis).

GNU Webster's 1913

1. n. (Zoöl.) a kind of beetle (Brachinus crepitans), so called because, when disturbed, it makes an explosive discharge of a pungent and acrid vapor from its anal glands. The name is applied to other related species, as the Brachinus displosor, which can produce ten or twelve explosions successively. The common American species is Brachinus fumans.

WordNet 3.0

1. n. beetle that ejects audibly a pungent vapor when disturbed