Қорғаныс шашыратқыш қоңыздар

Beetles that emit a spray when threatened

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 the abdomen with a popping sound. The spray is produced from a reaction between two hypergolic 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" (Eisner's word), catalysts facilitate the decomposition of the hydrogen peroxide and the oxidation of the hydroquinone. They typically live in woodlands or grasslands in the temperate zones but can be found in other environments if there are moist places to lay their eggs.

Most species of bombardier beetles are carnivorous, including the larva. The beetle typically hunts at night for other insects, but will often congregate with others of its species when not actively looking for food.

There are two large glands that open at the tip of the abdomen. Each gland is composed of a thick walled vestibule which contains a mixture of catalases and peroxidases produced by the secretory cells that line the vestibule. Both glands are also made up of a thin walled and compressible reservoir which contains an aqueous solution of hydroquinones and hydrogen peroxide.

The unique combination of features of the bombardier beetle's defense mechanism—strongly exothermic reactions, boiling hot fluids, and explosive release—has been claimed by creationists and proponents of intelligent design to be an example of irreducible complexity. Biologists such as the taxonomist Mark Isaak note however that step by step evolution of the mechanism could readily have occurred. The full evolutionary history of the beetle's unique defense mechanism is unknown, but biologists have shown that the system could have evolved from defenses found in other beetles in incremental steps by natural selection. Specifically, quinone chemicals are a precursor to sclerotin, a brownish substance produced by beetles and other insects to harden their exoskeleton. Some beetles additionally store excess foul smelling quinones, including hydroquinone, in small sacs below their skin as a natural deterrent against predators—all carabid beetles have this sort of arrangement. Some beetles additionally mix hydrogen peroxide, a common by product of the metabolism of cells, with the hydroquinone; some of the catalases that exist in most cells make the process more efficient. The chemical reaction produces heat and pressure, and some beetles exploit the latter to push out the chemicals onto the skin; this is the case in the beetle Metrius contractus, which produces a foamy discharge when attacked. In the bombardier beetle, the muscles that prevent leakage from the reservoir additionally developed a valve permitting more controlled discharge of the poison and an elongated abdomen to permit better control over the direction of discharge.