Bombardier beetle

From Wikipedia, the free encyclopedia

iBombardier beetles

Brachinus species

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Carabidae

Tribes

Brachinini
Paussini
Ozaenini
Metriini

Wikispecies has information related to:

Brachinini

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 posterior.

Bombardier beetles of all types are found on most continents of the world, generally in temperate zone woodlands or grasslands.

1 Defense mechanism
2 Intelligent design
3 Darwin's experience
4 References
5 External links

[edit] Defense mechanism

The mechanism works thus: Secretory cells produce hydroquinones and hydrogen peroxide (and perhaps other chemicals, depending on the species), 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 spray is aimed with precision accuracy, and can be pointed in any direction, even forward over its back by bouncing the spray off a pair of skeletal reflectors that it sticks out from the tip of its abdomen at the moment of ejection.) This effectively deters predators, often causing them blinding or death, and can be painful to human skin.

[edit] Intelligent design

Bombardier beetles have come to public attention in recent years largely because of arguments put forward by creationists, particularly in the children's book Bomby the Bombardier Beetle.^[1] The book argues that the beetles' internal design is an example of irreducible complexity, because various components needed to make the system work appear to provide no benefit in themselves, meaning the entire system would have to be created at once. According to the book this indicates that the beetle is the product of intelligent design.

However, researchers have shown that creationist claims were based on a misreading of research and that the chemical weapon involves minor alterations from systems in other, less noxious beetles.^[2] This lends weight to the idea that this beetle has diverged from other species as a product of evolution by natural selection.

In one demonstration, documented in the book The Blind Watchmaker, biologist Richard Dawkins mixed together hydroquinone and hydrogen peroxide in an artificial environment. No reaction occurred—a catalyst was required. Dawkins' point was that as the beetle's defensive mechanism evolved, the intermediate stages would not explode - the chemicals would not react without a catalyst.

[edit] Darwin's experience

During Charles Darwin's education at the University of Cambridge he became involved in a national craze for the competitive collecting of beetles. On one occasion in 1828 he stripped bark from a dead tree and caught a rare beetle in each hand, then saw another new species. With the habits of an egg-collector, he popped the beetle from his right hand into his mouth and grabbed the other with his free hand. The beetle which he had placed in his mouth, likely a bombardier beetle, "ejected some intensely acrid fluid, which burnt [his] tongue," forcing him to spit it out; he lost the beetle, as well as the third.^[3]

[edit] References

^ Bomby the Bombardier Beetle, by Hazel Rue, ISBN 0-932766-13-7
^ The Bombadier Beetle Myth Exploded--National Center for Science Education (Creation/Evolution Issue 03, Volume 2, Number 1 - Winter 1981)
^ Darwin: Young Naturalist. American Museum of Natural History. Retrieved on 2006-07-12.