A few odd members of the former family Ptinidae (now a part of Anobiidae) have taken to living with ants. Some of the most spectacular examples from the New World are species of the genus Fabrasia, all obligate nest inhabitants of Campanotus ants.
The various depressions and pits are notably sexy in this group. Also, they have enormously enlarged hind tibiae that house, what appear to be trichomes. Right off the top of my head, I cannot put my finger on any other beetle that houses such structures on their legs.
The United States has its share of myrmecophilous ptinines, such as Gnostus species from Florida.