Bombardier beetle

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Bombardier beetles
Brachinus species
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Coleoptera Family: Carabidae
Tribes
Brachinini Paussini Ozaenini Metriini

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.

Contents 1 Defense mechanism 2 Controversy: "Intelligent Design" 3 Darwin's experience 4 References 5 External links

[edit] Defense mechanism

The mechanism works like this: 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, aimed with precision, can be pointed in any direction, including forward over its back. This by bouncing the spray off a pair of skeletal reflectors stuck from the tip of its abdomen at the moment of ejection.) This makes a loud cracking or banging sound as the beetle shoots the spray, similar to a bursting balloon. This effectively deters predators, often causing blindness or death, and can be painful to human skin.

[edit] Controversy: "Intelligent Design"

Bombardier beetles have come to public attention in recent years largely because of various 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, claiming that various components needed to make the system work appear to provide no benefit in themselves and that 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.

In response, TalkOrigins Archive and the National Center for Science Education have published statements that the various creationist claims were based on a misreading or misunderstanding of research and that the chemical weapon could readily have evolved by numerous possible sequences of minor alterations from systems in other, less noxious beetles.^[2][3] They therefore consider that this beetle has diverged from other species as a product of evolution by natural selection.

[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.^[4]

[edit] References

[edit] External links

• Bombardier Beetles and the Argument of Design, from the talk.origins archive
• Proceedings of the National Academy of Sciences article: "Spray aiming in the bombardier beetle: Photographic evidence"
• Genus Brachinus--BugGuide.net
• Bombardier Idea from answersingenesis.org