Wikipedia
Zopherinae is a subfamily of beetles, commonly known as ironclad beetles. Together with the subfamily Usechinae, they have been treated historically as a family, but have recently been joined by several additional taxa, making the Zopheridae a much larger composite family, and the Zopherinae are now only a small component within it, consisting of seven genera in the tribe Zopherini and one genus, Phellopsis in its own tribe ( Phellopsini).
These beetles are apparently fungivores and associated with rotting wood, and as the common name implies, have one of the hardest of all arthropod exoskeletons; in some species, it is almost impossible to drive an insect pin through their bodies without using a small drill to make a hole first.
When disturbed, ironclad beetles play dead.
Some species in the genus Zopherus in Mexico are decorated with costume jewelry glued to their bodies, and sold as living brooches, known as ma'kech.