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Butterflies and insects have their skeletons on the outside of their bodies,
called the exoskeleton. This protects the insect and keeps water inside their bodies so they don’t dry out.
Like other arthropods, an insect’s external
skeleton, or exoskeleton, is made of semirigid plates and tubes. In insects, these plates are made of a plasticlike material
called chitin along with a tough protein. A waterproof wax covers the plates and prevents the insect’s internal tissues
from drying out.
Insect exoskeletons are highly effective as a body framework, but they have two drawbacks:
they cannot grow once they have formed, and like a suit of armor, they become too heavy to move when they reach a certain
size. Insects overcome the first problem by periodically molting their exoskeleton and growing a larger one in its place.
Insects have not evolved ways to solve the problem of increasing weight, and this is one of the reasons why insects are relatively
small.
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