bombardier beetle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various carabid beetles of the subfamily Brachininae that eject a hot, acrid spray from the abdomen when disturbed, making a popping sound.

from The Century Dictionary.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun beetle that ejects audibly a pungent vapor when disturbed