Instead of bones, insect bodies are supported by a skeleton that covers their outsides. This exoskeleton consists chiefly of chitin, a substance that can take forms raging from rubbery to rigid and from supple to steely. It not only protects the insect from damage or drying out, it also houses sensory organs, includes breathing holes called spiracles and, like our skeletons, provides a place for muscles to attach [sources: Encyclopedia Britannica, Meyer].
Exoskeletons also account for insects' notable strength and flexibility. Fixing internal muscles to an outer body wall instead of an inner skeleton boosts mechanical advantage, which partly explains why many insects can heft loads that weigh many times their own body weight. Insect bodies remain flexible thanks to supple tissues at the plate joints, and their internal squishiness lets them squeeze into small spaces to escape predators, seek food or hide from the elements [source: Meyer].
Like most adaptive features, exoskeletons have drawbacks. When an insect grows, its shell stays the same size, so it must shed it in a process called molting. After molting, the insect remains at risk until a new exoskeleton forms [sources: Encyclopedia Britannica]. Exoskeletons also limit how large insects can grow — in time, the need for more muscle outstrips available attachment areas — but that's just as well, because being small has survival value, too.