What is "bombardier beetle"

Bombardier \Bom`bar*dier"\, n. [F. bombardier.] (Mil.)

1. One who used or managed a bombard; an artilleryman; a gunner. [Archaic]

2. A noncommissioned officer in the British artillery.

   Bombardier beetle (Zo["o]l.), 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.

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: ''(taxlink Carabinae subfamily noshow=1)'' (e.g., (taxlink Brachinus crepitans species noshow=1)), ''(taxlink Metriinae subfamily noshow=1)'' (e.g., (taxlink Stenaptinus insignis species noshow=1)) and ''(taxlink Paussinae subfamily noshow=1)'' (e.g., (taxlink Goniotropis nicaraguensis species noshow=1)).

n. beetle that ejects audibly a pungent vapor when disturbed

Bombardier beetles are ground beetles (Carabidae) in the tribes Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species altogether—which are most notable for the defense mechanism that gives them their name: when disturbed, they eject a hot noxious chemical spray from the tip of their abdomen with a popping sound.

The spray is produced from a reaction between two chemical compounds, hydroquinone and hydrogen peroxide, which are stored in two reservoirs in the beetle's abdomen. When the aqueous solution of hydroquinones and hydrogen peroxide reaches the vestibule, catalysts facilitate the decomposition of the hydrogen peroxide and the oxidation of the hydroquinone. Heat from the reaction brings the mixture to near the boiling point of water and produces gas that drives the ejection. The damage caused can be fatal to attacking insects. Some bombardier beetles can direct the spray over a wide range of directions.