That annoying fly
that keeps landing on your sandwich... the irritating mosquito creating a high
pitched buzzing in your ear... the bumble bee that is drunkenly crawling around
in a flower… All these tiny
creatures form an amazingly diverse micro-world that most of us never think
very much about. One might think
that such small organisms can’t possibly be very complex, right? Wrong!! I’m taking an insect physiology course this semester and am
in awe and wonder of how brilliantly designed structures in insects create body systems
that are incredibly efficient in their functionality.
Let me share a few of
my “Wow!” statements with you…
The insect thorax
(middle segment) is basically ALL MUSCLE. The heat generated by these muscles
during flight has been picked up by infrared cameras. Some insects, like bees, even use these muscles to “shiver”
and warm themselves up in cold environments!
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| from: http://www.centralexterminatingco.com |
The inner layer of an insect’s exoskeleton, called the endocuticle, has a new layer added to
it each day. This means that if
you looked at a cross section of an insect you could count the rings to know
how many days it has been since the last molt, similar to counting rings in a
tree.
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| from: http://insectsdiditfirst.com |
Malpighian tubules: These are the insects’ version of
kidneys, functioning to get rid of wastes created by the normal functioning of
body cells. Malpighian tubules are small
dead-end tubes that connect to the digestive tract. One amazing feature of these tubules is that they are coated
with thin muscles that allow them to “wave” or “wiggle” through the hemolymph
(hemolymph = insect blood).
Another, even more fascinating, feature of the tubules is how they work
together with the rectum (last part of the digestive tract) to conserve water
and ions (salts). There is a flow
of water from the hemolymph, into the malpighian tubules, through the gut/rectum, and back into the hemolymph.
This flow of water is important because waste products that need to get
excreted are dissolved in the water.
But the water is not pumped in/out of these structures. The salts are what are actively pumped
through cells into the malpighian tubules and out of the rectum. The water flow
is simply a result of diffusion—the water follows the salts, trying to dilute
them! And, because of water’s
tendency to chase ions, the wastes dissolved in water get moved to the rectum for
excretion. But, insects are tiny
creatures that often do not have access to a lot of water. So it’s not enough for the water to
bring the waste to the rectum. The
waste needs to be left behind and the water and salts need to get recycled back
into the blood. This recycling
action is possible (in part) because there is a layer of exoskeleton on the
inside of the insect’s hindgut, creating a barrier that allows water and ions
to pass through but prevents the larger waste materials from going back into
the hemolymph. Amazing!
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| from: http://www.tutorvista.com |
Did you know insects actually have brains? The structure
and function of individual nerve cells
in insects in incredibly similar to the structure and function of nerves
in other animals, including humans.
The number of neurons in insects’ brains varies by species. There are about 1.2 million neurons in
a cockroach’s brain, 950,000 in a honey bee, and 200,000 in fruit flies. That’s a lot of neurons, but (not
surprisingly) comes nowhere close to the number of neurons found in the average
human brain which is around 100 billion.
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| from: http://www.animalbehavioronline.com |
Imaginal Discs: Have you ever wondered how adult
butterfly structures (like wings and unique mouthparts) that are not present in
caterpillars “magically” form inside the chrysalis? One important part of the answer is areas of cells called
imaginal discs. When a baby insect
is developing inside of the egg, there are often areas of embryological cells
that don’t grow and develop right away.
These “patches” of cells are present throughout the juvenile
caterpillar’s life and then become activated by hormones when metamorphosis
begins. The result is the
formation of adult insect structures.
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| from: http://www.scientificamerican.com |
A feature of insects that most everyone learns as a child is
that instead of an internal skeleton made of bones like vertebrates (including humans), they have an exoskeleton which supports and protects the insect, like a suit of armor. The exoskeleton is made up of distinct layers and has many
functions: protection, support, a
place for muscles to be anchored, coloration/camouflage, secretion of chemicals
for defense and communication, the gathering of sensory information,
temperature regulation, the prevention of water loss, and probably many
others. What is most amazing to
me, is that most of the exoskeleton is not made up of living cells. All of those functions are possible
because of one single layer of cells
at the base of the exoskeleton.
Though exoskeletons are basically designed to be strong and
rigid, some types/parts of an insect’s
exoskeleton can be stretchy. This adaptive feature allows for some
bizarre behaviors:
1.
A termite queen’s exoskeleton is able to stretch
to accommodate ridiculous amounts of eggs. She looks like a giant sausage inside the termite
colony. Some scientific studies
have reported that termite queens can lay an egg a second for long periods of
time (while the workers feed and tend and groom her).
2.
Some members of a honeypot ant colony are used as living storage organs for
the colony. When food is abundant, foraging workers bring nectar to the colony and deposit it into the
mouths/digestive tracts of some of
their sisters. These workers store
the food internally, swelling up like giant water
balloons. Then, when resources are
scarce, these "storage" ants feed the colony.
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| A honeypot ant from: http://weirdimals.wordpress.com |
You taste with your mouth. So do insects.
But some insects also have taste
receptors on their feet (like flies) or on their egg-laying structures
called ovipositors (like some wasps).
Do you think you’re so much different from an insect? Actually basic functions of living
things, like the production of proteins (which are basically how everything in
your cells works), the contraction of muscles, and metabolism (“burning”
nutrients and oxygen to make energy for cells to do their jobs) are essentially
the same in ALL LIVING THINGS.
Quite a bit is known about how insect hormones work to control the insects’ processes of molting
and metamorphosis. Interestingly
(or, depending on your perspective, disturbingly,) much of our understanding of
insect hormone functions came from experiments where scientists cut the heads
off of insects and/or strung a bunch of headless insects together. Knowing that an insect can live for
quite a long time without its head and
that key hormones needed for development are created in both the head and thorax is definitely
fascinating. But, I’m thinking
that those early scientists must have had a little bit of crazy in them to come up
with these experimental methods.
A male insect’s penis is called an aedeagus. Sometimes
the only way to tell the difference between males of different species is by
pulling out the aedeagus and examining its unique structure under a
microscope.
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| Some aedeagus diversity from: http://www.scielo.br |
Have you noticed some of the brilliant colors that occur in certain insects (especially beetles and
butterflies)? Many of the most
spectacular color patterns are not caused by chemical pigments, but by special
structures in the insect’s exoskeleton.
This microsculpturing of the exoskeleton causes different wavelengths of
light to be reflected, refracted or absorbed. The unique colors/patters caused by light work as a type of
communication between insects of the same species.
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| from: http://www.learnaboutbutterflies.com |
I could go on and on…
but I think that’s enough insect wonder for today...
“The poetry of the earth
is never dead.” –John Keats
“The heavens declare the
glory of God; the skies proclaim the work of his hands.”
–Psalm 19:1
“Complexity is the
prodigy of the world. Simplicity
is the sensation of the universe.
Behind complexity there is always simplicity to be revealed. Inside simplicity there is always
complexity to be discovered.” –Gang Yu
Yikes! Do you understand all of that?
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