Bombardier beetle

Bombardier Beetles are ground beetles (Carabidae) in the tribes Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species altogether—that are most notable for the defense mechanism that gives them their name: They can fire a mixture of chemicals from special glands in their abdomen.Taxobox
name = Bombardier beetles

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image_width = 205px
image_caption = "Brachinus" species
regnum = Animalia
phylum = Arthropoda
classis = Insecta
ordo = Coleoptera
familia = Carabidae
subdivision_ranks = Tribes
subdivision = Brachinini
Paussini
Ozaenini
Metriini

Bombardier beetles store two separate chemicals hydroquinone and hydrogen peroxide. When they are threatened, the two chemicals are squirted through two tubes, where they are mixed along with small amounts of catalytic enzymes and undergo a violent exothermic chemical reaction. The boiling, foul-smelling liquid partially becomes a gas (flash evaporation) and is expelled with a loud popping sound.

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 which are common in other beetles and have evolved as variations have been subject to natural selection. Various quinones 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 this to deter predators. Where there are indentations in the cuticle, these can vary to form little sacs which store the deterrent quinone. Where predators develop resistance to this chemical, other related chemicals such as hydroquinone can develop, and in many beetles specialised cells secreting hydroquinone form glands 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 which is a common by-product of the metabolism of cells can become mixed in with the hydroquinone, and some of the catalases which exist in most cells can make the process more efficient. The chemical reaction can produce warmth and pressure which pushes out the discharge when the insect is attacked, as in the beetle "Metrius contractus" which produces a foamy discharge, while a flap forms a valve to ensure that the pressure pushes the discharge out. In other bombardier beetles, muscles controlling the outlet have developed nozzles that can direct an increasingly explosive reaction to squirt the deterrent chemicals at an attacker. More detailed scenarios have been developed showing a series of small changes that could have led to this mechanism. [http://www.ncseweb.org/resources/articles/3955_issue_03_volume_2_number_1__2_21_2003.asp#The%20Bombadier%20Beetle%20Myth%20Exploded The Bombadier Beetle Myth Exploded] – National Center for Science Education ("Creation/Evolution" Issue 03, Volume 2, Number 1 - Winter 1981)] [http://www.talkorigins.org/faqs/bombardier.html Bombardier Beetles and the Argument of Design] by Mark Isaak, 1997, updated May 30, 2003, TalkOrigins Archive, retrieved 2007-07-09]

Creationist dispute

It has been claimed by some creationists such as Duane Gish that the various components needed to make the system work could not have evolved, as the components appeared to him to provide no benefit in themselves and therefore the entire system would have to be created at once. His presentation 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 practice catalysts are used to cause the reaction to start. Gish blamed a problem of translation leading him to misunderstand 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 in June 1984, and still on sale as of July 2007. [Citation
last = Rue
first = Hazel
date =June 1984
year = 1984
title =Bomby the Bombardier Beetle
publisher =Institute for Creation Research
isbn =0-932766-13-7] Its arguments have been described as riddled with errors. [Citation
last =Angier
first = Natalie
date =February 25, 1985
year = 1985
title =Drafting the Bombardier Beetle ^
publisher =Time Magazine
url =http://www.time.com/time/magazine/article/0,9171,961206-1,00.html
accessdate =2007-07-09]

In his 1996 book "Darwin's Black Box" the intelligent design creationist Michael Behe reviewed the same argument as "irreducible complexity" which he claimed to have found in various organisms, but he agreed that Darwinian evolution may possibly have been responsible for the formation of the Bombardier Beetle defensive system, as well as creationism. Another creationist analysis published by Answers in Genesis accepts much of the scientific view, but contends that complexity could suggest an origin by design.Citation
last = Armitage
first =Mark H.
last2 = Mullisen
first2 = Luke
date =April 2003
year = 2003
title =Preliminary observations of the pygidial gland of the Bombardier Beetle, Brachinus sp.
publisher =Answers in Genesis
url =http://www.answersingenesis.org/tj/v17/i1/beetle.asp
accessdate =2007-07-09]

References

External links

* [http://www.pnas.org/cgi/content/abstract/96/17/9705?ijkey=097c98acbdf7a2ee2d340f97a0459336c9f30c84&keytype2=tf_ipsecsha Proceedings of the National Academy of Sciences article: "Spray aiming in the bombardier beetle: Photographic evidence"]
* [http://bugguide.net/node/view/16725 Genus "Brachinus"--BugGuide.net]
* [http://jeb.biologists.org/cgi/content/abstract/203/8/1265 Journal of Experimental Biology "Spray mechanism of the most primitive bombardier beetle ("Metrius contractus")"] T Eisner, DJ Aneshansley, M Eisner, AB Attygalle, DW Alsop and J Meinwald, Journal of Experimental Biology, Vol 203, Issue 8 1265-1275, Copyright © 2000 by Company of Biologists
* [http://www.life-of-science.net/bio--and-nanotechnology/feature/exploding-beetles-suggest-a-new-pressure-relief-valve-and-fluid-discharge-system.html Overview feature about recent research on the fluid discharge mechanism in Bombardier beetles]

* [http://www.answersingenesis.org/creation/v27/i3/bombardier.asp Bombardier Idea] from Answers in Genesis
* [http://www.talkorigins.org/indexcc/CB/CB310.html Claim CB310: Bombardier beetle evolution] from TalkOrigins Archive
* [http://www.talkorigins.org/faqs/bombardier.html Bombardier Beetles and the Argument of Design] from TalkOrigins Archive