Home      Discussion      Topics      Dictionary      Almanac
Signup       Login
Bombardier beetle

Bombardier beetle

Overview
Bombardier beetles are ground beetle
Ground beetle
Ground beetles or carabids are collective terms for the beetle family Carabidae. This is a large family, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe....

s (Carabidae) in the tribe
Tribe (biology)
In biology, a tribe — or infrafamily — is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.-See also:* Rank * Rank *International Code of Botanical Nomenclature...

s Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species
Species
In biology, a species is:* a taxonomic rank or* a unit at that rank ....

 altogether—that are most notable for the defense mechanism that gives them their name: When disturbed, the beetle ejects a noxious chemical spray in a rapid burst of pulses from special gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s in its abdomen. The ejection is accompanied with a popping sound.

A bombardier beetle produces and stores two reactant chemical compounds, hydroquinone
Hydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound which is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position...

 and hydrogen-peroxide
Hydrogen peroxide
Hydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...

 in separate reservoirs in the rear tip of its abdomen.
Discussion
Ask a question about 'Bombardier beetle'
Start a new discussion about 'Bombardier beetle'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
Bombardier beetles are ground beetle
Ground beetle
Ground beetles or carabids are collective terms for the beetle family Carabidae. This is a large family, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe....

s (Carabidae) in the tribe
Tribe (biology)
In biology, a tribe — or infrafamily — is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.-See also:* Rank * Rank *International Code of Botanical Nomenclature...

s Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species
Species
In biology, a species is:* a taxonomic rank or* a unit at that rank ....

 altogether—that are most notable for the defense mechanism that gives them their name: When disturbed, the beetle ejects a noxious chemical spray in a rapid burst of pulses from special gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s in its abdomen. The ejection is accompanied with a popping sound.

A bombardier beetle produces and stores two reactant chemical compounds, hydroquinone
Hydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound which is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position...

 and hydrogen-peroxide
Hydrogen peroxide
Hydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...

 in separate reservoirs in the rear tip of its abdomen. When threatened, the beetle contracts muscles that force the two reactants through valved tubes into a mixing chamber containing water and a mixture of catalytic enzymes. When combined, the reactants undergo a violent exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light , electricity , or sound. Its etymology stems from the Greek prefix ex- and the Greek word thermein...

 chemical reaction raising the temperature to near the boiling point of water. The corresponding pressure buildup forces the entrance valves from the reactant storage chambers to close, thus protecting the beetle's internal organs. The boiling, foul-smelling liquid partially becomes a gas (flash evaporation
Flash evaporation
Flash evaporation is the partial vaporization that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through a throttling valve or other throttling device. This process is one of the simplest unit operations...

) and is expelled through an outlet valve into the atmosphere with a loud popping sound. The flow of reactants into the reaction chamber and subsequent ejection to the atmosphere occurs cyclically at a rate of about 500 times per second and with the total pulsation period lasting for only a fraction of a second.

The gland openings of some African bombardier beetles can swivel through 270° and thrust between the insect's legs so it can be discharged in all sorts of directions with considerable accuracy.

Defense mechanism


Secretory cells produce hydroquinones and hydrogen peroxide which collect in a reservoir. The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. This chamber is lined with cells that secrete catalases and peroxidases. When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones.

These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it. Under pressure of the released gasses the valve is forced closed, and the chemicals are expelled explosively through openings at the tip of the abdomen. Each time it does this it shoots about 70 times very rapidly. The damage caused can be fatal to attacking insects and small creatures and is painful to human skin.

Evolution of the defense mechanism


The defense mechanism uses features that are common in other beetles and have evolved
Evolution
In biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...

 as variations subjected to natural selection
Natural selection
Natural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...

. Various quinone
Quinone
Quinones are "compounds having a fully conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of –CH= groups into –C– groups with any necessary rearrangement of double bonds ."Benzoquinone, sometimes referred to simply as...

s are commonly produced by cells in the skin of insects to harden their skin into a cuticle, and as they taste bad to predators, many insects secrete them to deter predators. Where there are indentations in the cuticle, these vary to form little sacs that store the deterrent quinone. Where predators develop resistance to this chemical, other related chemicals such as hydroquinone
Hydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound which is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position...

 develop, and in many beetles specialised cells secreting hydroquinone form gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...

s connected by ducts to a reservoir sac, which can be closed off by muscles to stop leakage. While all carabid beetles have this sort of arrangement, in some cases Hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...

, which is a common by-product of the metabolism of cells, is mixed in with the hydroquinone, and some of the catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms which are exposed to oxygen, where it functions to catalyze the decomposition of hydrogen peroxide to water and oxygen...

s that exist in most cells makes the process more efficient. The chemical reaction produces heat and pressure, which pushes out the discharge when the insect is attacked, as in the beetle Metrius contractus, which produces a foamy discharge. In other bombardier beetles, the muscles stopping leakage have a flap forming a valve to ensure that the pressure pushes the discharge out, and muscles controlling the outlet have developed nozzles that can direct an explosive reaction to squirt the deterrent chemicals at an attacker. The exact sequence is unknown, and it is common for features with one purpose to become useful for other purposes. More detailed scenarios have been developed showing a series of small changes that could have led to this mechanism.

Creationist dispute


It has been claimed by some creationists
Creationism
Creationism refers to the religious belief that humanity, life, the Earth, and the universe were created in some form by a supernatural being or beings, commonly a single deity...

, such as Duane Gish
Duane Gish
Duane Tolbert Gish is an American biochemist who is one of the most prominent and outspoken members of the creationist movement. Gish is a former vice-president of the Institute for Creation Research and the author of numerous publications on the subject of creation science.Gish has been called...

, that the various components needed to make the system work could not have evolved, as they claim that the components provide no benefit in themselves and therefore the entire system would have to have been created at once. Gish has mistakenly stated that the hydrogen peroxide and hydroquinone would explode on contact and that the beetle adds an inhibitor to keep this from happening, when in actuality, catalysts are used to start the reaction. In response, Gish blamed his misunderstanding on a problem of translation from his German source, but continued to use his description in debates.
A similar argument is set out in the children's book Bomby the Bombardier Beetle (ages 4–8), published by the Institute for Creation Research
Institute for Creation Research
The Institute for Creation Research is a Christian institution in Dallas, Texas that specializes in education, research, and media promotion of creation science and Biblical creationism. The ICR adopts the Bible as an inerrant and literal documentary of scientific and historical fact as well as...

 in June 1984, which is still on sale . Time
Time (magazine)
Time is an American newsmagazine. A European edition is published from London. Time Europe covers the Middle East, Africa and, since 2003, Latin America. An Asian edition is based in Hong Kong. As of 2009, Time no longer publishes a Canadian advertiser edition...

 described the book as "so riddled with errors that entomologists cannot begin to guess where [the author] got her information".

In his 1996 book Darwin's Black Box, the intelligent design
Intelligent design
Intelligent design is the assertion that "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection." It is a modern form of the traditional teleological argument for the existence of God, but one which...

 creationist Michael Behe
Michael Behe
Michael J. Behe is an American biochemist and intelligent design advocate. He currently serves as professor of biochemistry at Lehigh University in Pennsylvania and as a senior fellow of the Discovery Institute's Center for Science and Culture...

 reviewed the same argument as an example of "irreducible complexity
Irreducible complexity
Irreducible complexity is an argument by proponents of intelligent design that certain biological systems are too complex to have evolved from simpler, or "less complete" predecessors, through natural selection acting upon a series of advantageous naturally occurring chance mutations...

", which he claimed to have found in various organisms, but he agreed that Darwinian natural selection may possibly have been responsible for the formation of the bombardier beetle defensive system.

Another creationist analysis published by Answers in Genesis
Answers in Genesis
Answers in Genesis is a non-profit Christian apologetics ministry with a particular focus on Young Earth creationism and a literal interpretation of the Book of Genesis. The organization has offices in the United Kingdom and the United States...

 accepts much of the scientific view, but contends that complexity suggests an origin by design.

External links