The name of this order comes from the Greek words koleos and pteron, which mean sheath and wing respectively, and Aristotle is credited with coming up with the term Coleoptera, the name we still use today for the beetle insect order.
Beetles have hardened (ossified) forewings, which act as a protective case, and they use the hindwings for flying; these wingcases are called elytra.
The earliest beetle fossils date from around 300 million years ago. Beetles also have a broad shield behind the head, which is really just the upper plate of the first segment of the thorax, referred to by entomologists as the pronotum.
Beetles have a range of different defence mechanisms, and we have a couple of examples:
Firstly these Lychee stink bugs, huddling together at night.
They have a directional anal sphincter which can blast noxious chemicals onto predators, and I have friends who have blisters from harvesting lychees from these beetles. Toads will vomit them up when its stomach starts to burn.
And how about this pretty little beetle, the Ladybird?
Ladybirds are unpalatable to most birds, and they can squeeze their noxious orange/yellow blood through special pores in their knees. Yikes!