While there are a million different types of insects, all have a hard exoskeleton which is segmented into three parts. In fact the word "insect" is derived from the Latin meaning segmented.
How Cockroaches Work
Entomologists estimate that there are between 5 and 10 million species of insects on Earth. But if asked which insect they hate the most, many people would have no trouble choosing just one -- the cockroach.