We occasionally get identification requests for ironclad beetles, usually from Texas. These insects are a bit of a mystery because no one is sure of what they eat, or anything else about them for that matter. Texas A&M has a fact sheet, and there is a rather short page at Wikipedia. The adults are thought to feed on lichens, and the food source of the larvae is unknown but may be fungi in rotting trees. These are a real mystery in this age of knowing a pretty good amount about insects, especially the big and showy ones such as these.