Bombadier Beetle
Stenaptinus insignis
& relatives

What Kind of Animal is It?

The bombadier beetle is an Invertebrate animal (it has no backbone). Its
phylum is the Arthropoda, a group with an external skeleton (exoskeleton) made
of a hard substance called chitin. The external skeleton allows these animals to
have joints and gives them a much greater range of motion than is found in
simpler organisms (compare an earthworm with a butterfly). Arthropods can swim,
crawl, run, jump and fly.

Bombadier beetles are in the Insect class because they have antennae, 3 pairs
of legs and a body divided into a head, thorax and abdomen. Within the insects,
they are in the order Coleoptera, the beetles. In the beetles the forewings
(called elytra) are hard and form a protective cover for the posterior wings. It
is estimated that there are more than 300,000 kinds of beetles, by far the
largest order of the insects.

What is its Lifestyle?

Bombadiers are carabid beetles, adapted for running rapidly along the ground
or up trees. They feed mostly on other insects and must avoid being eaten
themselves.

Like many insects beetles have a comlex reproduction, involving several
developmental stages and metamorphosis from a larval stage to an adult
forms.

Chemical Warfare in the Bombadier
Beetles

The most notable thing about bombadier beetles is that they engage in
chemical warfare in a spectacular way, spraying a hot caustic liquid when
disturbed. The chemical reactions have been studied in detail and are fairly
well understood:

At Rest:

The bombadier beetle secretes 2 highly reactive substances from 2
different glands into a reservoir:

Hydrogen peroxide: you can buy this in a drugstore for sterilizing
cuts. There is a difference: the bombadier stores it at a 10X higher
concentration than the drugstore variety. At this concentration it
would produce a nasty burn if you pit it on your skin

Hydroquinone: you can buy this at a photography store. It is a
powerful reducing agent, sometimes used in film developers

These 2 chemicals are stored in the same reservoir. They do not
explode because they react slowly under these conditions

A second chamber has the enzymes that can accelerrate the reaction
to a rapid rate, but a ring of muscle (sphincter) keeps the reactants
from mixing with the enzyme

When Excited:

If the beetle is excited the sphincter relaxes and opens

Muscles around the starage chamber contract, forcing the reactants
out, into the enzyme chamber

This allows the reactants to contact the enzymes

The reaction accelerates explosively

Solution is heated above the boiling point of water

The hydroquinone is converted to toxic benzoquinone

Heat causes pressure to build up within the chamber

The high pressure causes the hot, toxic liquid to spray from two
jets

The bombadier has muscles with which to aim the jets toward his
enemy

When biologists see a mechanism like this, the first question is: how does it
work. The second question is likely to be: how did it come about (evolve)? We
have answered the first question fairly well, but the second is much more
difficult.

This is certainly a complex defensive mechanism,
one that you probably would not expect to find in nature. To biologist Michael
Behe mechanisms of this sort are examples of "irreducible complexity", that is
they are so complicated that they could not have evolved. He beleives that they
are evidence of intelligent design (creation) in nature. However, he admits that
there are many possible "evolutionary intermediates" seen in other beetles who
have only part of the bombadier's elaborate defense mechanism. For example:

Some beetles use the quinones simply to make themselves taste bad

Many beetles and other organisms make hydrogen peroxide for defensive
purposes

The enzyme that speeds up the reaction is found in most cells, including
some of ours

Some types of bombadiers have a weak chemical reaction which produces a
warm, but not hot secretion

This leads most biologists to beleive that the elaborate bombadier defense
mechanism could have evolved step-by-step over a period of time. Somehow it is
not very satisfactory to explain every tough biological puzzle by saying, "and
then a miracle occured".

Some Things to Think About

How does the bombadier avoid harming himself when he is spraying an
attacker?

Should those who support the idea of creation be required to give a more
complete analysis? For example:

Why was this system created?

How many miracles were required?

How much of the mechanism could have resulted from natural processes?

More Information

Michael J. Behe. Darwin's Black Box. NY: Free Press, 1996. This is
probably the best written of the books supporting the creation idea in
biology.

To see a spectacular picture of a bombadier in action and for information
on the chemistry go to this site run by the chemistry department of the Universite
Laval in Quebec, Canada. Your textbook has a nice picture of a bombadier
on p. 617

Eisner T, Aneshansley DJ. Spray aiming in the bombadier beetle:
photographic evidence. Proceedings of the National Academy of Sciences, USA
1999; 96:9705-9709. More beautiful pictures of bombadies spraying (Stenaptinus
insignis, from Kenya)

For those of you who like to argue, here are 2 websites with quite different
ideas on how the bombadier beetle got here:

The Talk.Origins Archive
discusses the evidence for Creation vs Evolution. This site has a definite
evolutionist bias.

The Ultimate
Creation/Evolution website also discusses the Creation vs Evolution
controversy, but from a decidedly creationist bias.

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