Aptinus pyrenaeus belongs to the brachinini, a group of ground beetles who can spectacularly expel a cloud of chemical substance when attacked or threatened. Their very large abdominal cavities are filled with liquid consisting of hydrogenic peroxide and hydroquinone. When threatened, this liquid goes to a reservoir, wich is protected by very thick sides, and which serves as a reaction chamber. In this chamber enzymes, catalases and peroxydases, start a very quick and violent reaction. The oxygen and quinones produced by the reaction, produce a sufficient amount of heath to make the liquid boil. The whole substance is then expelled through anal glands, causing bluish or whitish clouds with temperatures of up to 100 degrees Celsius!