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2-12-02
A Tale of Blood and Guts of the
Insect Type
Some time back, I received a letter with a request
to identify insects that a homeowner had discovered in his house. Were
they ants? Termites? Or something even worse? The insects were enclosed
in a small plastic bag. The envelope--and its contents--had been processed
through an automated stamp-canceling machine. And, in this case, more
than the stamp was cancelled. The insects were smashed to smithereens.
Now smashing insects is not something new to humans.
We smack insects every chance that we get. Fly swatters were invented
for just that purpose. But we will use our hands, newspapers and even
our hats as insect-whacking devices when necessary.
Whenever we are successful in smacking an insect
what remains doesn't bear much resemblance to the intact creature. To
be sure, you can sometimes find an identifiable wing, a leg or two, and
maybe even an antenna, but the most obvious remnant is a greasy, gooey
little spot. We're talking insect blood and guts here.
Most people have some notion about how the outside
of an insect looks. You know, it has three major body sections. There
is a head in the front with a mouth, eyes and antennae. A middle section,
with wings and legs attached, called the thorax is next. Then comes the
abdomen, which literally brings up the rear. But most people don't think
much about insect guts. At least, not until they look at their hand after
terminating a fly or when they struggle to clean the car windshield after
a warm summer night's drive.
The blood and guts of insects are every bit as
important to them as our innards are to us. However, there are some differences.
Both insects and humans have important fluids that flow through the body.
We call ours blood. In insects, that fluid is called hemolymph.
Human blood flows through a series of tubes. On
the way to the heart, those tubes are veins; away from the heart and lungs,
the tubes are arteries. Insects don't have a series of tubes to transmit
such fluid. The insect hemolymph just sloshes around in a bag--a bag that
we call the insect body. Scientifically, the human system is closed. Insects,
therefore, have an open system.
Closed and open is not the only difference in the
internal fluid systems of insects and humans. In mammals, including humans,
blood carries oxygen to the cells and carbon dioxide away. The exchange
occurs in the lungs. It is a red substance called hemoglobin that is the
carrier, which is why our blood is red.
The insect blood does not carry oxygen. It lacks
hemoglobin and is not red, except in a very few insects. For example,
aquatic larvae of a group of flies called chironomids are known as bloodworms
because they have hemoglobin in their blood. This is also true of the
larva of a bot fly and a bug called a backswimmer. But the hemolymph of
most insects is either colorless or yellow in color.
Another major component of insect innards is the
digestive tract. It would normally contain food in various states of digestion.
The inside of an insect would also include what is known as fat body.
Insects, like humans, store energy in the form of fat. In insects, the
fat is stored in specialized cells that are located throughout the inside
of the insect.
So the next time you see a smashed insect don't
just think greasy, grimy insect guts. Be scientific and think hemolymph,
undigested gut contents and fat body cells! And look closely, because
there ought to be some wings and legs thrown in there somewhere.
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