Teaching Guide to Exoskeletons
Overview:
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Roles of An Exoskeleton
○ a protective covering over the body
○ a surface for muscle attachment
○ a water-tight barrier against desiccation
○ a sensory interface with the environment.
It is a multi-layered structure.
It is a “non-cellular structure”, made of chitin
○ When chitin combines with the protein sclerotin it creates a multi-layerd
exoskeleton with the basic properties of plastic: tough yet light and flexible.
The exoskeleton is divided into smaller sections/plates called “sclerites”. These are
fused together to form distinct body regions and their appendages. They are joined by
membranes of pure chitin or are separated by grooves called sutures. This allows for
greater flexibility like a knight's armor. These plates are NOT the separation between
body segments, they can be seen on the underbelly of some beetles.
Sometimes called “the secret to insect success”
Water Proofing:
● The ​epicuticle​ is the outermost part of the cuticle. Its function is to reduce water loss
and block the invasion of foreign matter. The innermost layer of epicuticle is often
called the ​cuticulin layer​, a stratum composed of lipoproteins and chains of fatty acids
embedded in a protein-polyphenol complex. An oriented monolayer of w
​ ax molecules
lies just above the cuticulin layer; it serves as the chief barrier to movement of water into
or out of the insect's body. In many insects a ​cement layer​ covers the wax and protects
it from abrasion.
● The waterproof wax covering is secreted by glands embeded in the lower levels of the
exoskeleton. Helps to retain body moisture.
Pros & Cons of Exoskeletons
Pro
Con
Protection
Small Size
Body Part Regeneration
Transformation
Coloration
Camouflage
Unique modifications
Molting
Limited to Small size
Arthropod/Beetle Strength:
The exoskeleton penetrates the body forming a complex framework of internal supports that
provide attachments for powerful muscles that drive the mouthparts, legs and wings.
Exoskeletons are sensory too, not just antennas:
On beetles the outer layer of the exoskeleton (cuticle) are “setae”. They sometimes are hair like
in nature and are sensory in nature. They transmit tactile and odor information to the nervous
system. Can also be protection if clumped in strategic places to reduce abrasion and wear and
tear.
Blue Death Feigning Beetles:
The wax filaments that they secrete makes them blue! These wax filaments are secreted by
glands whose spigots open at the tips of the knoblike bumps on the wing covers (elytra). The
filaments spread over the upper surface of the body, creating a meshwork that functions as
deep sea diving suit in reverse, sealing off the beetle from its dry surroundings to keep water
inside the body.
Scarab Beetles:
These guys eat ant larva and ant colonies can be dangerous places to be as an intruder.
Scarab beetles have adapted by having exoskeletons that allow them to tuck away sensitive
antennae and mouthparts to keep them away from angry ants. Also, the surface of their
exoskeleton has nooks and crannies, like an english muffin, that absorbs the odor of the ants
nest so they don’t alarm the ants. (They also have glands that let off an odor that calms angry
ants!)
Why an exoskeleton:
For terrestrial animals, endoskeletons (internal skeletons like a humans) are more efficient for
animals of a larger size. Exoskeletons are more efficient with a smaller body size. From an
engineer's POV an insect is a set of hollow tubes. For the weight, a tube is more resistant to
buckling than is a solid rod. But, as an animal is bigger and bigger, hollow tubes can no longer
support that weight. Skeletons of larger animals have more stress from impacts and there is
cushioning from soft matter around the skeleton.